阅读说明：本技术 有受保护的石墨碳阴极层的多价金属离子电池及制造方法 (Polyvalent metal ion battery with protected graphitic carbon cathode layer and method of manufacture ) 是由 阿茹娜·扎姆 张博增 于 2018-03-02 设计创作，主要内容包括：提供一种多价金属离子电池,其包括阳极、阴极、以及电解质,所述电解质与所述阳极和所述阴极处于离子接触以负载所述阳极处的多价金属的可逆的沉积和溶解,所述多价金属选自Ni、Zn、Be、Mg、Ca、Ba、La、Ti、Ta、Zr、Nb、Mn、V、Co、Fe、Cd、Cr、Ga、In、或其组合,其中所述阳极含有作为阳极活性材料的所述多价金属或其合金,并且所述阴极包含涂覆有保护材料的石墨碳颗粒或纤维的阴极活性层。此种金属离子电池给予高能量密度、高功率密度以及长循环寿命。(There is provided a multivalent metal ion battery comprising an anode, a cathode, and an electrolyte In ionic contact with the anode and the cathode to support reversible deposition and dissolution of a multivalent metal at the anode, the multivalent metal selected from Ni, Zn, Be, Mg, Ca, Ba, La, Ti, Ta, Zr, Nb, Mn, V, Co, Fe, Cd, Cr, Ga, In, or combinations thereof, wherein the anode contains the multivalent metal or alloy thereof as an anode active material, and the cathode comprises a cathode active layer of graphitic carbon particles or fibers coated with a protective material. Such metal-ion batteries impart high energy density, high power density, and long cycle life.)

1. a polyvalent metal-ion battery comprising an anode, a cathode, and an electrolyte In ionic contact with the anode and the cathode to support reversible deposition and dissolution of a polyvalent metal at the anode, the polyvalent metal selected from Ni, Zn, Be, Mg, Ca, Ba, La, Ti, Ta, Zr, Nb, Mn, V, Co, Fe, Cd, Cr, Ga, In, or combinations thereof, wherein the anode contains the polyvalent metal or alloys thereof as an anode active material, and the cathode comprises a cathode active layer of graphitic carbon particles or fibers as a cathode active material that intercalates/deintercalates ions of the polyvalent metal, and wherein the graphitic carbon particles or fibers are coated with a protective layer that is permeable to ions of the polyvalent metal or ions dissolved In the electrolyte and that prevents or reduces expansion of graphitic planes In the graphitic carbon particles or fibers And (4) transforming.

2. The multivalent metal ion battery of claim 1, wherein the graphitic carbon particles or fibers in the cathode active layer are selected from mesophase pitch, Mesophase Carbon Microbeads (MCMB), coke particles/needles, expanded graphite flakes, artificial graphite particles, natural graphite particles, amorphous graphite containing graphite crystallites, highly oriented pyrolytic graphite, soft carbon particles, hard carbon particles, multi-walled carbon nanotubes, carbon nanofibers, carbon fibers, graphite nanofibers, graphite fibers, carbonized polymer fibers, or combinations thereof.

3. The polyvalent metal-ion battery of claim 1, wherein said graphitic carbon fibers in said cathode active layer comprise needle coke, carbon nanofibers, carbon fibers, graphitic nanofibers, graphitic fibers, multiwall carbon nanotubes, or combinations thereof, and said graphitic carbon fibers have a length shorter than 10 μm.

4. The multivalent metal ion battery of claim 1, wherein the protective layer comprises a material selected from the group consisting of: reduced graphene oxide, a carbonized resin, an ion conducting polymer, a conductive polymer, or a combination thereof.

5. The multivalent metal ion battery of claim 4, wherein the conductive polymer is selected from polyaniline, polypyrrole, polythiophene, polyfuran, bicyclic polymers, derivatives thereof, or combinations thereof.

6. The multivalent metal ion battery of claim 4, wherein the ionically conductive polymer is selected from the group consisting of sulfonated polymers, poly (ethylene oxide) (PEO), polypropylene oxide (PPO), poly (acrylonitrile) (PAN), poly (methyl methacrylate) (PMMA), poly (vinylidene fluoride) (PVdF), poly bis (methoxyethoxyethanol-phosphazene), polyvinyl chloride, polydimethylsiloxane, poly (vinylidene fluoride) -hexafluoropropylene (PVDF-HFP), or combinations thereof.

7. The multivalent metal ion battery of claim 6, wherein the sulfonated polymer may be selected from the group consisting of: poly (perfluorosulfonic acid), sulfonated poly (tetrafluoroethylene), sulfonated perfluoroalkoxy derivatives of polytetrafluoroethylene, sulfonated polysulfone, sulfonated poly (ether ketone), sulfonated poly (ether ketone), sulfonated polyimide, sulfonated styrene-butadiene copolymers, sulfonated polystyrene, sulfonated Polychlorotrifluoroethylene (PCTFE), sulfonated perfluoroethylene-propylene copolymers (FEP), sulfonated ethylene-chlorotrifluoroethylene copolymers (ECTFE), sulfonated polyvinylidene fluoride (PVDF), sulfonated copolymers of polyvinylidene fluoride with hexafluoropropylene and tetrafluoroethylene, sulfonated copolymers of Ethylene and Tetrafluoroethylene (ETFE), Polybenzimidazole (PBI), chemical derivatives thereof, copolymers thereof, blends thereof, and combinations thereof.

8. The multivalent metal ion battery of claim 1, wherein the graphitic carbon particles or fibers have a hard carbon or amorphous carbon surface that is at least partially removed prior to being coated with the protective layer.

9. The multivalent metal ion battery of claim 1, further comprising an anode current collector supporting the multivalent metal or alloy thereof or further comprising a cathode current collector supporting the cathode active layer of graphite or carbon material.

10. The multivalent metal ion battery of claim 9, wherein the anode current collector comprises a unified nanostructure of conductive nano-scale filaments interconnected to form a porous network of electron conducting pathways comprising interconnected pores, wherein the filaments have a transverse dimension of less than 500 nm.

11. The multivalent metal ion battery of claim 10, wherein the filaments comprise a conductive material selected from the group consisting of: electrospun nanofibers, vapor grown carbon or graphite nanofibers, carbon or graphite whiskers, carbon nanotubes, nanoscale graphene platelets, metal nanowires, and combinations thereof.

12. The multivalent metal ion battery of claim 1, wherein the electrolyte is selected from an aqueous electrolyte, an organic electrolyte, a polymer electrolyte, a molten salt electrolyte, an ionic liquid electrolyte, or a combination thereof.

13. The multivalent metal ion battery of claim 1, wherein the electrolyte contains NiSO4, ZnSO4, MgSO4, CaSO4, BaSO4, FeSO4, MnSO4, CoSO4, VSO4, TaSO4, CrSO4, CdSO4, GaSO4, Zr (SO4)2, Nb2(SO4)3, La2(SO4)3, BeCl2, BaCl2, MgCl2, AlCl3, Be (ClO4)2, Ca (ClO4)2, Mg (ClO4)2, Mg (BF4)2, Ca (BF4) bu2, Be (BF4)2, grignard reagent, tris (3, 5-dimethylphenyl borane, tris (pentafluorophenyl) borane, dibutyldiphenylmagnesium Mg (BPh 2h 2)2, buryl magnesium (b 2), Mg (b 84), bpb 3, or a combination thereof.

14. The multivalent metal ion battery of claim 1, wherein the electrolyte comprises at least one metal ion salt selected from the group consisting of: transition metal sulfates, transition metal phosphates, transition metal nitrates, transition metal acetates, transition metal carboxylates, transition metal chlorides, transition metal bromides, transition metal nitrides, transition metal perchlorates, transition metal hexafluorophosphates, transition metal fluoroborates, transition metal hexafluoroarsenates, or combinations thereof.

15. The multivalent metal ion battery of claim 1, wherein the electrolyte comprises at least one metal ion salt selected from the group consisting of: metal sulfates, phosphates, nitrates, acetates, carboxylates, nitrides, chlorides, bromides, or perchlorates of zinc, aluminum, titanium, magnesium, calcium, beryllium, manganese, cobalt, nickel, iron, vanadium, tantalum, gallium, chromium, cadmium, niobium, zirconium, lanthanum, or combinations thereof.

16. The multivalent metal ion battery of claim 1, wherein the electrolyte comprises an organic solvent selected from the group consisting of: ethylene Carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (MEC), diethyl carbonate (DEC), Methyl Butyrate (MB), ethyl propionate, methyl propionate, Propylene Carbonate (PC), γ -butyrolactone (γ -BL), Acetonitrile (AN), Ethyl Acetate (EA), Propyl Formate (PF), Methyl Formate (MF), Tetrahydrofuran (THF), toluene, xylene, Methyl Acetate (MA), or a combination thereof.

17. The multivalent metal ion battery of claim 1, wherein the electrolyte further supports reversible intercalation and de-intercalation of ions at the cathode, wherein the ions comprise cations, anions, or both.

18. The multivalent metal ion battery of claim 1, wherein the cathode active layer of carbon or graphite material functions as a cathode current collector to collect electrons during discharge of the multivalent metal ion battery, and wherein the battery is free of a separate or additional cathode current collector.

19. The multivalent metal ion battery of claim 1, wherein the cathode active layer of carbon or graphite further comprises a binder material that binds the carbon or graphite material together to form a cathode electrode layer.

20. The multivalent metal ion battery of claim 19, wherein the binder comprises a conductive material selected from the group consisting of: coal tar pitch, petroleum pitch, mesophase pitch, conductive polymers, polymeric carbon, or derivatives thereof.

21. The multivalent metal ion battery of claim 1, wherein the battery has an average discharge voltage of not less than 1.0 volt and a specific capacity of the cathode of greater than 200mAh/g based on total cathode active layer weight.

22. The multivalent metal ion battery of claim 1, wherein the battery has an average discharge voltage of not less than 2.0 volts and a specific capacity of the cathode of greater than 300mAh/g based on total cathode active layer weight.

23. The multivalent metal ion battery of claim 1, wherein the battery has an average discharge voltage of not less than 3.0 volts and a specific capacity of the cathode of greater than 200mAh/g based on total cathode active layer weight.

24. A method of manufacturing a multivalent metal ion battery, the method comprising:

(a) Providing an anode comprising a polyvalent metal or alloy thereof, wherein the polyvalent metal is selected from the group consisting of Ni, Zn, Be, Mg, Ca, Ba, La, Ti, Ta, Zr, Mn, V, Co, Fe, Cd, Cr, Ga, In, or combinations thereof;

(b) Providing a cathode active layer of graphitic carbon particles or fibers as a cathode active material that intercalates/deintercalates ions; and

(c) Providing an electrolyte capable of supporting reversible deposition and dissolution of the multivalent metal at the anode and reversible adsorption/desorption and/or intercalation/de-intercalation of ions at the cathode;

Wherein the graphitic carbon particles or fibers are coated with a protective layer that is permeable to ions of the polyvalent metal or ions dissolved in the electrolyte and which prevents or reduces puffing of graphite planes in the graphitic carbon particles or fibers during charge/discharge cycles of the battery.

25. The method of claim 24, further comprising providing a porous network of conductive nanofilaments to support the multivalent metal or alloy thereof.

26. The method of claim 24, wherein the graphitic carbon particles or fibers in the cathode active layer are selected from mesophase pitch, Mesophase Carbon Microbeads (MCMB), coke particles/needles, expanded graphite flakes, artificial graphite particles, natural graphite particles, amorphous graphite containing graphite crystallites, highly oriented pyrolytic graphite, soft carbon particles, hard carbon particles, multi-walled carbon nanotubes, carbon nanofibers, carbon fibers, graphite nanofibers, graphite fibers, carbonized polymer fibers, or combinations thereof.

27. the method of claim 24, wherein the step of providing a cathode active layer comprises a procedure of cutting needle coke, carbon nanofibers, carbon fibers, graphite nanofibers, graphite fibers, or multi-walled carbon nanotubes to obtain graphitic carbon fibers having an average length shorter than 10 μ ι η.

28. The method of claim 24, wherein the protective layer comprises a material selected from the group consisting of: reduced graphene oxide, a carbonized resin, an ion conducting polymer, a conductive polymer, or a combination thereof.

29. The method of claim 24, wherein the graphitic carbon particles or fibers have a hard carbon or amorphous carbon surface that is at least partially removed prior to being coated with the protective layer.

30. The method of claim 24, wherein the electrolyte comprises an aqueous electrolyte, an organic electrolyte, a polymer electrolyte, a molten salt electrolyte, an ionic liquid, or a combination thereof.

Technical Field

the present invention relates generally to the field of rechargeable polyvalent metal batteries (e.g., zinc ion batteries, nickel ion batteries, calcium ion batteries, or magnesium ion batteries, etc.), and more particularly to a cathode layer containing graphitic carbon particles or fibers and a method of making the polyvalent metal ion battery.

Background

Historically, the most popular rechargeable energy storage devices today-lithium ion batteries-were actually developed from rechargeable "lithium metal batteries" that use lithium (Li) metal as the anode and a Li intercalation compound (e.g., MoS2) as the cathode. Li metal is an ideal anode material due to its light weight (the lightest metal), high electronegativity (-3.04V versus standard hydrogen electrode), and high theoretical capacity (3,860 mAh/g). Based on these outstanding characteristics, lithium metal batteries were proposed 40 years ago as an ideal system for high energy density applications.

Due to some safety issues with pure lithium metal, graphite is implemented as the anode active material instead of lithium metal to produce current lithium ion batteries. The last two decades have witnessed a continuous improvement in Li-ion batteries in terms of energy density, rate capability and safety. However, the use of graphite-based anodes in Li-ion batteries has several significant drawbacks: low specific capacity (372 mAh/g theoretical capacity versus 3,860mAh/g for Li metal), long Li intercalation time (e.g. low solid state diffusion coefficient of Li into and out of graphite and inorganic oxide particles) requires long recharge time (e.g. 7 hours for electric vehicle batteries), does not give high pulse power, and requires the use of pre-lithiated cathodes (e.g. lithium cobalt oxide versus cobalt oxide), thus limiting the choice of usable cathode materials. Further, these commonly used cathode active materials have relatively low lithium diffusion coefficients (typically D is about 10-16 to 10-11cm 2/sec). These factors have contributed to one of the major drawbacks of today's Li-ion batteries-medium energy density (typically 150-220Wh/kg cells), but very low power density (typically <0.5 kW/kg).

Ultracapacitors are being considered for Electric Vehicles (EV), renewable energy storage, and modern grid applications. The relatively high bulk capacitance density of supercapacitors (10 to 100 times greater than that of electrolytic capacitors) stems from the use of porous electrodes to create a large surface area conducive to the formation of a diffused double-layer charge. This Electric Double Layer Capacitance (EDLC) occurs naturally at the solid electrolyte interface when a voltage is applied. This means that the specific capacitance of a supercapacitor is directly proportional to the specific surface area of the electrode material (e.g. activated carbon). This surface area must be accessible to the electrolyte, and the resulting interface area must be large enough to accommodate the EDLC charge.

This EDLC mechanism is based on surface ion adsorption. The desired ions are pre-existing in the liquid electrolyte and not coming from the opposite electrode. In other words, the desired ions to be deposited on the surface of the negative electrode (anode) active material (e.g., activated carbon particles) do not come from the positive electrode (cathode) side, and the desired ions to be deposited on the surface of the cathode active material do not come from the anode side. When the supercapacitor is recharged, localized positive ions deposit near the surface of the negative electrode, with their delustering negative ions residing close side-by-side (typically through localized molecular or ionic polarization of the charge). At the other electrode, negative ions are deposited close to the surface of this positive electrode, with the extinction positive ions residing close side-by-side. Also, there is no ion exchange between the anode active material and the cathode active material.

In some supercapacitors, the stored energy is further increased by pseudocapacitance effects due to some local electrochemical reactions (e.g. redox reactions). In such a pseudocapacitor, the ions involved in the redox couple are also pre-existing in the same electrode. Also, there is no ion exchange between the anode and the cathode.

Since the formation of EDLCs does not involve chemical reactions or ion exchange between two opposing electrodes, the charging or discharging process of EDL supercapacitors can be very fast, typically within a few seconds, resulting in very high power densities (typically 3-10 kW/kg). Compared to batteries, supercapacitors provide higher power densities, do not require maintenance, provide much higher cycle lives, require very simple charging circuits, and are generally much safer. Physical rather than chemical energy storage is a key reason for its safe operation and exceptionally high cycle life.

Despite the positive attributes of supercapacitors, several technical hurdles remain for the wide implementation of supercapacitors in various industrial applications. For example, supercapacitors have very low energy densities when compared to batteries (e.g., commercial supercapacitors at 5-8Wh/kg versus 10-30Wh/kg for lead acid batteries, and NiMH batteries at 50-100 Wh/kg). Modern lithium ion batteries have much higher energy densities, typically in the range of 150-220Wh/kg based on cell weight.

In addition to lithium ion cells, there are several other different types of batteries that are widely used in society: alkaline Zn/MnO2, nickel metal hydride (Ni-MH), lead-acid (Pb acid), and nickel-cadmium (Ni-Cd) cells. Since 1860 its invention, alkaline Zn/MnO2 batteries have become very popular primary (non-rechargeable) batteries. It is now known that a Zn/MnO2 pair can constitute a rechargeable battery if an acidic salt electrolyte is used instead of an alkaline (basic/alkaline) salt electrolyte. However, the cycle life of alkaline manganese dioxide rechargeable cells is typically limited to 20-30 cycles due to irreversibility associated with MnO2 upon deep discharge and formation of an electrochemically inert phase.

In addition, when Zn penetrates into the lattice structure of MnO2, a haeteriolite (ZnO: Mn2O3) phase is formed during discharge causing the cell to cycle irreversibly. Zn anodes also have limitations on cycle life due to redistribution of Zn active material and formation of dendrites (resulting in internal short circuits) during recharging. Oh et al [ S.M.Oh and S.H.Kim, "Aqueous Zinc Sulfate (II) Rechargeable cells Containing Manganese (II) salts and Carbon powders ]," U.S. Pat. No. 6,187,475,2001, 2.13.d. ] and Kang et al [ F.Kang et al, "Rechargeable Zinc Ion Battery", "U.S. Pat. No. 8,663,844,2014, 3.4.d. ] have attempted to solve some of these problems. However, long-term cycling stability and power density issues remain to be solved. For these reasons, commercialization of this battery is limited.

Xu et al, U.S. publication No. 20160372795(12/22/2016) and U.S. publication No. 20150255792(09/10/2015) report Ni and Zn ion cells, respectively, both using graphene sheets or Carbon Nanotubes (CNTs) as cathode active materials. Although these two patent applications require exceptionally high specific capacities of 789-:

(1) Unlike typical lithium ion batteries, there is no plateau in the charge or discharge curve (voltage versus time or voltage versus specific capacity). The lack of this voltage curve plateau means that the output voltage is not constant (varies too much) and will require complex voltage adjustment algorithms to maintain the cell output voltage at a constant level.

(2) In fact, once the discharge process begins, the discharge curve of the Ni ion cell exhibits an extremely sharp drop from 1.5 volts to below 0.6 volts, and during most discharge processes, the cell output is below 0.6 volts, which is not very useful. For reference, an alkaline cell (primary battery) provides an output voltage of 1.5 volts.

(3) In contrast to ionic intercalation, the discharge curve is characteristic of the surface adsorption or plating mechanism at the cathode. Further, it appears that the primary event occurring at the cathode during cell discharge is electroplating. The high specific capacity values reported by Xu et al are merely a reflection of the large amount of Ni or Zn metal plated on the surface of graphene or CNT. The amount of metal plated increases with the increase of discharge time due to the presence of an excessive amount of Ni or Zn in the anode. Unfortunately, the electrochemical potential difference between the anode and cathode continues to decrease as the difference in the amount of metal between the anode and cathode continues to decrease (more Zn or Ni dissolves from the anode and is plated onto the cathode surface). This may be the reason why the cell output voltage continues to decrease. When the amount of metal at both electrodes is substantially equal or identical, the cell voltage output will be substantially zero. Another implication of this electroplating mechanism is the following point: the total amount of metal that can be deposited on the bulk surface at the cathode is determined by the amount of metal implemented at the anode when the cell is fabricated. The high specific capacity of the graphene sheets at the cathode (up to 2,500mAh/g) reflects only an excessively high amount of Zn provided in the anode. There is no other reason or mechanism why graphene or CNTs can "store" such polymetallic. The exceptionally high specific capacity values as reported by Xu et al are artificially obtained based on the large amount of Ni or Zn plated on the surface of the cathode material, which unfortunately occurs at very low voltage values and has little utility value.

Clearly, there is an urgent need for new cathode materials that provide appropriate discharge voltage profiles (with high average voltage and/or high plateau voltage during discharge), high specific capacities at both high and low charge/discharge rates (not just at low rates), and long cycle life of multivalent metal secondary batteries. Hopefully, the resulting battery may give some positive attributes of supercapacitors (e.g., long cycle life and high power density) as well as some positive features of lithium ion batteries (e.g., medium energy density). These are the main objects of the present invention.

Disclosure of Invention

The present invention provides a polyvalent metal-ion battery comprising an anode, a cathode, and an electrolyte In ionic contact with the anode and the cathode to support reversible deposition and dissolution of a polyvalent metal at the anode, the polyvalent metal being selected from Ni, Zn, Be, Mg, Ca, Ba, La, Ti, Ta, Zr, Nb, Mn, V, Co, Fe, Cd, Cr, Ga, In, or combinations thereof, wherein the anode contains a polyvalent metal or alloy thereof as an anode active material, and the cathode comprises a cathode active layer of graphitic carbon particles or fibers as a cathode active material that intercalates/deintercalates ions of the polyvalent metal (and/or ions dissociated from the electrolyte), and wherein the graphitic carbon particles or fibers are coated with a protective layer that is permeable to ions of the polyvalent metal or ions dissolved In the electrolyte and that is electrically protective at the anode Preventing or reducing puffing of graphite planes in the graphitic carbon particles or fibers during cell charge/discharge.

The graphitic carbon particles or fibers in the cathode active layer may preferably be selected from mesophase pitch, Mesophase Carbon Microspheres (MCMB), coke particles/needles, expanded graphite flakes, artificial graphite particles, natural graphite particles, amorphous graphite containing graphite crystallites, highly oriented pyrolytic graphite, soft carbon particles, hard carbon particles, multiwalled carbon nanotubes, carbon nanofibers, carbon fibers, graphite nanofibers, graphite fibers, carbonized polymer fibers, or combinations thereof.

In some preferred embodiments, the graphitic carbon fibers in the cathode active layer comprise needle coke, carbon nanofibers, carbon fibers, graphitic nanofibers, graphitic fibers, or multi-walled carbon nanotubes, said graphitic carbon fibers having a length shorter than 10 μm, preferably shorter than 5 μm, and more preferably shorter than 1 μm. It was found that shorter lengths lead to higher rate performance and higher power density.

We have surprisingly observed that intercalation and de-intercalation of ions into and out of graphitic carbon structures can cause expansion and separation (puffing) of the graphite planes (graphene planes), compromising the structural integrity of the cathode electrode. Accordingly, a protective coating is deposited on the surface of the graphitic carbon particles or fibers to prevent or reduce puffing of the graphite planes in the graphitic carbon particles or fibers during battery charge/discharge. The protective layer may contain a material selected from the group consisting of: reduced graphene oxide, a carbonized resin, an ion conducting polymer, a conductive polymer, or a combination thereof. The protective coating may partially or completely cover the entire surface of the graphitic carbon particles or fibers to hold the graphitic planes together (for the purpose of maintaining the structural integrity of the particles/fibers) but still allow ions to permeate through so that ions can intercalate into the graphitic structure.

this protective material may be selected from reduced graphene oxide (wrapped around the graphitic carbon particles), carbonized resins (or polymeric carbons), ion-conducting polymers (e.g., sulfonated polymers), and electrically conducting polymers. The polymeric carbon may be selected from polymers with low carbon content (e.g. epoxy or polyethylene) or high carbon content (e.g. phenolic or polyacrylonitrile) which are heat treated at 500-1500 ℃ for 1-10 hours. The conductive polymer may be selected from polyaniline, polypyrrole, polythiophene, polyfuran, bicyclic polymers, derivatives thereof (e.g., sulfonated versions), or combinations thereof.

In some embodiments, the ionically conductive polymer is selected from the group consisting of sulfonated polymers, Poly (ethylene oxide) (PEO), polypropylene oxide (PPO), Poly (acrylonitrile) (PAN), Poly (methyl methacrylate) (PMMA), Poly (vinylidene fluoride) (PVdF), Poly bis-methoxy ethoxy ethoxide-phosphazene (Poly bis-methoxy ethoxy thereby-phosphonzenex), polyvinyl chloride, polydimethylsiloxane, Poly (vinylidene fluoride) -hexafluoropropylene (PVdF-HFP), and combinations thereof.

The sulfonated polymer may be selected from the group consisting of: poly (perfluorosulfonic acid), sulfonated poly (tetrafluoroethylene), sulfonated perfluoroalkoxy derivatives of polytetrafluoroethylene, sulfonated polysulfone, sulfonated poly (ether ketone), sulfonated poly (ether ketone), sulfonated polyimide, sulfonated styrene-butadiene copolymers, sulfonated polystyrene, sulfonated Polychlorotrifluoroethylene (PCTFE), sulfonated perfluoroethylene-propylene copolymers (FEP), sulfonated ethylene-chlorotrifluoroethylene copolymers (ECTFE), sulfonated polyvinylidene fluoride (PVDF), sulfonated copolymers of polyvinylidene fluoride with hexafluoropropylene and tetrafluoroethylene, sulfonated copolymers of Ethylene and Tetrafluoroethylene (ETFE), Polybenzimidazole (PBI), chemical derivatives thereof, copolymers thereof, blends thereof, and combinations thereof.

In certain embodiments, the graphitic carbon particles or fibers have a hard carbon or amorphous carbon surface that is at least partially removed prior to being coated with the protective layer. The hard carbon skin is impermeable to certain ions (larger cations or anions) and must therefore be at least partially removed. Many graphite materials inherently have a hard carbon skin. These include mesophase carbon, mesophase carbon microspheres, needle coke, carbon nanofibers, carbon fibers, graphite nanofibers, and graphite fibers.

We have observed that selected polyvalent metals (e.g., Ni, Zn, Be, Mg, Ca, Ba, La, Ti, Ta, Zr, Nb, Mn, V, Co, Fe, Cd, Ga, In, or Cr) may exhibit a discharge curve plateau at about 1.0 volts or higher (e.g., from 0.85 to 3.8 volts) when coupled with the graphitic carbon materials of the invention. This plateau state of the discharge voltage versus time (or capacity) curve enables the battery cell to provide a useful constant voltage output. Voltage outputs significantly below 1 volt are generally considered undesirable. The specific capacity corresponding to this plateau state is typically from about 100mAh/g to over 600 mAh/g.

This multivalent metal ion battery may further comprise an anode current collector supporting the multivalent metal or alloy thereof, or further comprise a cathode current collector supporting the cathode active layer. The current collector may be a mat, paper, fabric, foil, or foam composed of conductive nanofilaments, such as graphene sheets, carbon nanotubes, carbon nanofibers, carbon fibers, graphite nanofibers, graphite fibers, carbonized polymer fibers, or combinations thereof, forming a 3D network of electron conducting pathways. The high surface area of such an anode current collector not only facilitates rapid and uniform dissolution and deposition of metal ions, but also serves to reduce the exchange current density and thus the tendency to form metal dendrites that would otherwise cause internal short circuits.

In the multivalent metal ion battery of the present invention, the electrolyte may contain NiSO4, ZnSO4, MgSO4, CaSO4, BaSO4, FeSO4, MnSO4, CoSO4, VSO4, TaSO4, CrSO4, CdSO4, GaSO4, Zr (SO4)2, Nb2(SO4)3, La2(SO4)3, BeCl2, BaCl2, MgCl2, AlCl3, Be (ClO4)2, Ca (ClO4)2, Mg (ClO4)2, Mg (BF4)2, Ca (BF4)2, bube (BF4)2, tris (3, 5-dimethylphenyl borane, tris (pentafluorophenyl) borane, alkyl grignard reagent, dibutyldiphenylmagnesium Mg (BPh 2h 2)2, bub 2 Mg (BF 737) 2), tris (bpb 3), or a combination thereof.

In certain embodiments of the present invention, the electrolyte comprises at least one metal ion salt selected from: transition metal sulfates, transition metal phosphates, transition metal nitrates, transition metal acetates, transition metal carboxylates, transition metal chlorides, transition metal bromides, transition metal perchlorates, transition metal hexafluorophosphates, transition metal fluoroborates, transition metal hexafluoroarsenates, or combinations thereof.

In certain embodiments, the electrolyte comprises at least one metal ion salt selected from: a metal sulfate, phosphate, nitrate, acetate, carboxylate, chloride, bromide, or perchlorate salt of zinc, aluminum, titanium, magnesium, beryllium, calcium, manganese, cobalt, nickel, iron, vanadium, tantalum, gallium, chromium, cadmium, niobium, zirconium, lanthanum, or a combination thereof.

In the polyvalent metal-ion battery, the electrolyte comprises an organic solvent selected from the group consisting of: ethylene Carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (MEC), diethyl carbonate (DEC), Methyl Butyrate (MB), ethyl propionate, methyl propionate, Propylene Carbonate (PC), γ -butyrolactone (γ -BL), Acetonitrile (AN), Ethyl Acetate (EA), Propyl Formate (PF), Methyl Formate (MF), Tetrahydrofuran (THF), toluene, xylene, Methyl Acetate (MA), or a combination thereof.

In certain embodiments, the layer of carbon or graphite material functions as a cathode current collector to collect electrons during discharge of the battery, and wherein the battery does not contain a separate or additional cathode current collector.

The cathode active layer of graphite may further comprise a conductive binder material that binds the particles or fibers of carbon or graphite material together to form a cathode electrode layer. The conductive binder material may be selected from coal tar pitch, petroleum pitch, mesophase pitch, conductive polymers, polymeric carbons, or derivatives thereof.

Typically, the secondary battery of the invention has an average discharge voltage of no less than 1 volt (typically from 1.0 to 3.8 volts) and a cathode specific capacity of greater than 200mAh/g (preferably and more typically >300mAh/g, more preferably >400mAh/g, and most preferably >500mAh/g) based on total cathode active layer weight. Some cells gave specific capacities of >600 mAh/g.

Preferably, the secondary battery has an average discharge voltage of not less than 2.0 volts (preferably >2.5 volts and more preferably >3.0 volts) and a cathode specific capacity of greater than 100mAh/g (preferably and more typically >300mAh/g, more preferably >400mAh/g, and most preferably >500mAh/g) based on total cathode active layer weight.

The invention also provides a method of manufacturing a multivalent metal ion battery. The method comprises the following steps: (a) providing an anode comprising a polyvalent metal (selected from the group consisting of Ni, Zn, Mg, Ca, Ba, La, Ti, Ta, Zr, Nb, Mn, V, Co, Fe, Cd, Cr, Ga, In, or combinations thereof) or alloys thereof; (b) providing a cathode active layer of graphitic carbon particles or fibers as a cathode active material that intercalates/deintercalates ions; and (c) providing an electrolyte capable of supporting reversible deposition and dissolution of the multivalent metal at the anode and reversible adsorption/desorption and/or intercalation/de-intercalation of ions at the cathode; wherein the graphitic carbon particles or fibers are coated with a protective layer that is permeable to ions of the polyvalent metal or ions dissolved in the electrolyte and which prevents or reduces puffing of graphite planes in the graphitic carbon particles or fibers during charge/discharge cycles of the battery.

In the method, the graphitic carbon particles or fibers in the cathode active layer are selected from mesophase pitch, Mesophase Carbon Microspheres (MCMB), coke particles/needles, expanded graphite flakes, artificial graphite particles, natural graphite particles, amorphous graphite containing graphite crystallites, highly oriented pyrolytic graphite, soft carbon particles, hard carbon particles, multi-walled carbon nanotubes, carbon nanofibers, carbon fibers, graphite nanofibers, graphite fibers, carbonized polymer fibers, or combinations thereof.

The step of providing a cathode active layer may comprise a procedure of cutting needle coke, carbon nanofibers, carbon fibers, graphite nanofibers, graphite fibers, or multi-walled carbon nanotubes to obtain graphite carbon fibers having an average length of less than 10 μm, preferably less than 5 μm and more preferably less than 1 μm. It was found that shorter lengths enable higher power densities of the resulting metal ion cells.

The protective layer may contain a material selected from the group consisting of: reduced graphene oxide, a carbonized resin, an ion conducting polymer, a conductive polymer, or a combination thereof. The graphitic carbon particles or fibers may have a hard carbon or amorphous carbon surface that is at least partially removed prior to being coated with the protective layer. The electrolyte contains an aqueous electrolyte, an organic electrolyte, a polymer electrolyte, a molten salt electrolyte, an ionic liquid, or a combination thereof.

The method may further comprise providing a porous network of conductive nanofilaments to support the multivalent metal or alloy thereof.

Drawings

Fig. 1(a) a schematic of a polyvalent metal secondary battery, wherein the anode layer is a thin coating or foil of a polyvalent metal and the cathode active material layer contains a layer of graphitic carbon particles or fibers with a protective coating; and

Fig. 1(B) a schematic of a polyvalent metal secondary battery cell, wherein the anode layer is a thin coating or foil of a polyvalent metal and the cathode active material layer is composed of graphitic carbon particles or fibers with a protective coating, a conductive additive (not shown), and a resin binder (not shown).

Fig. 2 discharge curves of two cells based on Zn foil anodes; one cell contains a cathode layer of pristine graphite fibers and the other cell contains a cathode layer of surface treated graphite fibers with the hard carbon skin removed.

Fig. 3 discharge curves of two Ca ion cells: one cell contains a cathode layer of Carbon Nanofibers (CNF) without a hard carbon skin (skin that has been chemically etched away), and the other cell contains a cathode layer of CNF with a hard carbon skin.

Fig. 4 is a discharge curve of two cells based on Ni grid anodes; one cell contained the cathode layer of virgin MCMB particles and the other cell contained the cathode layer of surface-treated MCMB particles.

Fig. 5 specific capacities of two V-needle coke cells (one cell containing a sulfonated PVDF protected needle coke cathode and the other cell containing an unprotected needle coke cathode) plotted as a function of charge/discharge cycle number.

Fig. 6 specific capacities of two Mg ion cells, one containing the cathode layer of MWCNTs protected by carbonized phenolic resin and the other containing the cathode layer of unprotected MWCNTs. The electrolyte used was 1M MgCl2: AlCl3(2:1) in ethylene glycol dimethyl ether.

Fig. 7 plots of ralong (Ragone) for two Ti ion cells, one with a cathode having surface treated MCMB and the other with untreated MCMB.

Detailed Description

As schematically illustrated in the upper portion of fig. 1(a), bulk natural graphite is a 3-D graphite material in which each graphite particle is composed of a plurality of grains (the grains are graphite single crystals or crystallites) having grain boundaries (amorphous or defect regions) that define adjacent graphite single crystals. Each grain is composed of a plurality of graphene planes oriented parallel to each other. The graphene planes or hexagonal carbon atom planes in the graphite crystallites are composed of carbon atoms occupying a two-dimensional hexagonal lattice. In a given grain or single crystal, graphene planes are stacked in the crystallographic c-direction (perpendicular to the graphene plane or basal plane) and bound by van der waals forces. The inter-planar spacing of the graphene in the natural graphite material is about 0.3354 nm.

Artificial graphite materials, such as Highly Oriented Pyrolytic Graphite (HOPG), also contain constituent graphene planes, but they typically have an interplanar spacing d002 of graphene from 0.336nm to 0.365nm as measured by X-ray diffraction. Both natural and artificial graphite have physical densities typically >2.1g/cm3, more typically >2.2g/cm3, and most typically very close to 2.25g/cm 3.

Many carbon or quasi-graphitic materials (referred to herein as graphitic carbon) also contain graphitic crystals (also referred to as graphitic crystallites, domains, or grains) each made up of stacked graphene planes. However, the structures typically have a high proportion of amorphous or defective regions. These include mesocarbon microbeads (MCMB), mesocarbon, soft carbon, hard carbon, coke (e.g., needle coke), and carbon or graphite fibers (including vapor grown carbon or graphite nanofibers). Multi-wall carbon nanotubes (MW-CNTs) do have few defects or amorphous parts, but each CNT has a tubular structure. Thus, multi-walled CNTs have a physical density of about 1.35g/cm 3. Other types of graphitic carbon have typical densities below 2.1g/cm3, and more typically below 2.0g/cm3, even more typically <1.9g/cm3, and most typically <1.8g/cm 3.

It may be noted that "soft carbon" refers to a carbon material containing graphitic domains, wherein the orientation of the hexagonal carbon planes (or graphene planes) in one domain and the orientation in the adjacent graphitic domains are not so different or mismatched from each other that these domains can easily merge together when heated to temperatures above 2,000 ℃ (more typically above 2,500 ℃). Such heat treatment is commonly referred to as graphitization. Thus, soft carbon may be defined as a carbon-containing material that can be graphitized. In contrast, "hard carbon" may be defined as a carbonaceous material containing highly misoriented graphitic domains that cannot thermally merge together to obtain larger domains; that is, hard carbon cannot be graphitized.

The present invention provides a multivalent metal secondary battery comprising an anode, a cathode, optionally a porous separator electronically separating the anode and the cathode, and an electrolyte in ionic contact with the anode and the cathode to support reversible deposition and dissolution of the multivalent metal at the anode, wherein the anode contains a multivalent metal or metal alloy thereof as an anode active material, and the cathode comprises a layer of graphitic carbon particles or fibers (filaments), preferably selected from the group consisting of mesocarbon particles, mesocarbon microbeads (MCMB), coke particles or needles, soft carbon particles, hard carbon particles, amorphous graphite containing graphitic crystallites, multiwalled carbon nanotubes, carbon nanofibers, carbon fibers, graphite nanofibers, graphite fibers, or combinations thereof. These graphitic carbon fibers or particles are coated with a thin layer of protective material.

We have observed that some graphitic carbon materials, such as mesophase carbon particles, Mesophase Carbon Microspheres (MCMB), coke particles or needles, soft carbon particles, hard carbon particles, carbon nanofibers, carbon fibers, graphite nanofibers, and graphite fibers, have a thin skin of hard carbon naturally formed on their surfaces when producing these synthetic graphitic carbon particles or fibers. We have surprisingly observed that it is very beneficial to subject these particles or fibres to a surface treatment (e.g. surface chemical etching, surface plasma cleaning, etc.) to remove some or all of the hard carbon on their outer surfaces.

In certain preferred embodiments, graphitic carbon (e.g., mesophase carbon particles, MCMB, coke particles or needles, soft carbon particles, hard carbon particles, amorphous graphite, multiwall carbon nanotubes, and carbon nanofibers), with or without the above-described surface treatment, may be coated with a protective layer that is permeable to polyvalent metal ions or ions dissolved in the electrolyte and prevents or reduces puffing of graphite planes in the graphitic carbon particles or fibers. We have surprisingly observed that repeated intercalation/de-intercalation into and out of graphitic crystallites or domains via polyvalent metal ions and other electrolyte-derived ions may lead to expansion of the inter-planar spaces between graphene planes and swelling of the graphene planes (hexagonal carbon atom planes). This effect, while initially increasing the charge storage capacity of the cathode material, subsequently leads to severe graphene planar puffing to the point of compromising the structural integrity of the cathode layer and the rapid decay of the charge storage capacity. By depositing a thin layer of protective material on the surface of the graphitic carbon particles or fibres, the structural integrity and cycling stability of the cathode layer can be significantly improved.

This protective material may be selected from reduced graphene oxide (wrapped around the graphitic carbon particles), carbonized resins (or polymeric carbons), ion-conducting polymers (e.g., sulfonated polymers), and electrically conducting polymers. The reduced graphene oxide sheets have many naturally occurring surface defects (pores) that are permeable to all ions of interest. The polymeric carbon may be selected from polymers with low carbon content (e.g. epoxy or polyethylene) or high carbon content (e.g. phenolic or polyacrylonitrile). The conductive polymer may be selected from polyaniline, polypyrrole, polythiophene, polyfuran, bicyclic polymers, derivatives thereof (e.g., sulfonated versions), or combinations thereof.

In some embodiments, the ionically conductive polymer is selected from the group consisting of sulfonated polymers, poly (ethylene oxide) (PEO), polypropylene oxide (PPO), poly (acrylonitrile) (PAN), poly (methyl methacrylate) (PMMA), poly (vinylidene fluoride) (PVdF), poly bis-methoxyethoxyethanol-phosphazene, polyvinyl chloride, polydimethylsiloxane, poly (vinylidene fluoride) -hexafluoropropylene (PVdF-HFP), combinations thereof.

Sulfonation also creates pores that are permeable to metal ions. The sulfonated polymer may be selected from the group consisting of: sulfonated poly (perfluorosulfonic acid), sulfonated poly (tetrafluoroethylene), sulfonated perfluoroalkoxy derivatives of polytetrafluoroethylene, sulfonated polysulfone, sulfonated poly (ether ketone), sulfonated poly (ether ketone), sulfonated polyimide, sulfonated styrene-butadiene copolymers, sulfonated polystyrene, sulfonated Polychlorotrifluoroethylene (PCTFE), sulfonated perfluoroethylene-propylene copolymers (FEP), sulfonated ethylene-chlorotrifluoroethylene copolymers (ECTFE), sulfonated polyvinylidene fluoride (PVDF), sulfonated copolymers of polyvinylidene fluoride with hexafluoropropylene and tetrafluoroethylene, sulfonated copolymers of Ethylene and Tetrafluoroethylene (ETFE), Polybenzimidazole (PBI), chemical derivatives thereof, copolymers thereof, blends thereof, and combinations thereof.

The configuration of the polyvalent metal secondary battery is now discussed as follows:

A multivalent metal ion battery includes a positive electrode (cathode), a negative electrode (anode), and an electrolyte that typically includes a metal salt and a solvent. The anode may be a thin foil or film of a polyvalent metal or alloy thereof with one or more another element; for example 0-10% by weight Sn in Zn. The polyvalent metal may Be selected from Ni, Zn, Be, Mg, Ca, Ba, La, Ti, Ta, Zr, Nb, Mn, V, Co, Fe, Cd, Cr, Ga, In, or combinations thereof. The anode may be comprised of particles, fibers, wires, tubes or disks of a polyvalent metal or metal alloy which are stacked and bonded together by a binder, preferably an electrically conductive binder, to form the anode layer.

We have observed that selected polyvalent metals (e.g., Ni, Zn, Be, Mg, Ca, Ba, La, Ti, Ta, Zr, Mn, V, Co, Fe, Cd, Ga, or Cr) can exhibit a discharge curve plateau or average output voltage at about 1.0 volt or higher when coupled with the graphite or carbon material of the present invention having expanded inter-graphene-planar spaces. This plateau state of the discharge voltage versus time (or capacity) curve enables the battery cell to provide a useful constant voltage output. Voltage outputs below 1 volt are generally considered undesirable. The specific capacity corresponding to this platform state is typically from about 100mAh/g (e.g., for Zr or Ta) to over 600mAh/g (e.g., for Zn or Mg).

The desired anode layer structure consists of a network of electron conducting paths (e.g. a graphene sheet, a mat of carbon nanofibers or carbon nanotubes) and a thin layer of a polyvalent metal or alloy coating deposited on the surface of this conducting network structure. Such integrated nanostructures may be comprised of conductive nanofilaments that are interconnected to form a porous network of electronically conductive pathways comprising interconnected pores, wherein the filaments have a transverse dimension of less than 500 nm. Such filaments may comprise an electrically conductive material selected from the group consisting of: electrospun nanofibers, vapor grown carbon or graphite nanofibers, carbon or graphite whiskers, carbon nanotubes, nanoscale graphene platelets, metal nanowires, and combinations thereof. Such nanostructured porous support materials for multivalent metals can significantly improve metal deposition-dissolution kinetics at the anode, thereby enabling high rate performance of the resulting multivalent metal secondary cell.

Shown in fig. 1(a) is a schematic of a polyvalent metal secondary battery in which the anode layer is a thin coating or foil of a polyvalent metal and the cathode active material layer contains a layer of graphitic carbon fibers or particles, optionally a resin binder (not shown), and optionally a conductive additive (not shown). Alternatively, fig. 1(B) shows a schematic of a polyvalent metal secondary battery cell in which the cathode active material layer is composed of particles or fibers of graphitic carbon material and a resin binder (not shown) that helps to bind the particles or fibers together to form a cathode active layer having structural integrity.

When implemented as a cathode active material, the surface treated and/or surface protected graphitic carbon material enables multivalent metal ion cells to exhibit a voltage plateau portion in the discharge voltage-time or voltage-capacity curve obtained at constant current density. This plateau portion typically occurs at relatively high voltage values inherent to a given polyvalent metal, and typically lasts for a long time, resulting in a high specific capacity.

The composition of the electrolyte used as an ion transport medium for charge-discharge reactions has a large influence on the battery performance. In order to put the polyvalent metal secondary battery into practical use, it is necessary to allow the metal ion deposition-dissolution reaction to proceed smoothly and sufficiently even at a relatively low temperature (e.g., room temperature).

In the polyvalent metal-ion battery of the present invention, the electrolyte typically contains a metal salt dissolved in a liquid solvent. The solvent may be water, organic liquids, ionic liquids, organic-ionic liquid mixtures, and the like. In certain desirable embodiments, the metal salt may be selected from NiSO4, ZnSO4, MgSO4, CaSO4, BaSO4, FeSO4, MnSO4, CoSO4, VSO4, TaSO4, CrSO4, CdSO4, GaSO4, Zr (SO4)2, Nb2(SO4)3, La2(SO4)3, MgCl2, AlCl3, Mg (ClO4)2, Mg (BF4)2, alkyl grignard reagent, dibutyl diphenyl magnesium Mg (BPh2Bu2)2, tributylphenyl magnesium Mg (BPhBu3)2), or combinations thereof.

The electrolyte may typically comprise at least one metal ion salt selected from: transition metal sulfates, transition metal phosphates, transition metal nitrates, transition metal acetates, transition metal carboxylates, transition metal chlorides, transition metal bromides, transition metal nitrides, transition metal perchlorates, transition metal hexafluorophosphates, transition metal fluoroborates, transition metal hexafluoroarsenates, or combinations thereof.

in certain embodiments, the electrolyte comprises at least one metal ion salt selected from: a metal sulfate, phosphate, nitrate, acetate, carboxylate, chloride, bromide, nitride, or perchlorate salt of zinc, aluminum, titanium, magnesium, calcium, manganese, cobalt, nickel, iron, vanadium, tantalum, gallium, chromium, cadmium, niobium, zirconium, lanthanum, or a combination thereof.

In the polyvalent metal-ion battery, the electrolyte comprises an organic solvent selected from the group consisting of: ethylene Carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (MEC), diethyl carbonate (DEC), Methyl Butyrate (MB), ethyl propionate, methyl propionate, Propylene Carbonate (PC), γ -butyrolactone (γ -BL), Acetonitrile (AN), Ethyl Acetate (EA), Propyl Formate (PF), Methyl Formate (MF), Tetrahydrofuran (THF), toluene, xylene, Methyl Acetate (MA), or a combination thereof.

The present invention relates to a cathode active layer (positive electrode layer) containing a high-capacity cathode material for a polyvalent metal secondary battery. The invention also provides such a battery based on an aqueous electrolyte, a non-aqueous electrolyte, a molten salt electrolyte, a polymer gel electrolyte (e.g. containing metal salts, liquids and polymers dissolved in a liquid), or an ionic liquid electrolyte. The shape of the polyvalent metal secondary battery may be cylindrical, square, button, or the like. The present invention is not limited to any battery shape or configuration.

The following examples are intended to show some of the specific details of the best mode for practicing the invention and should not be interpreted as limiting the scope of the invention.

Example 1: cathode layer containing needle coke

A commercially available needle coke (Jinzhou Petrochemical Co) was used to prepare the cathode active material layer. Both surface treated and untreated needle coke powders were investigated. A sample of surface treated needle coke (needle coke filament) was prepared by immersing the filament in concentrated sulfuric acid for 2 hours to remove the hard carbon skin. The washed and dried powder was then mixed with PVDF binder in a solvent (NMP) to form a slurry, which was coated on a carbon paper sheet (as a current collector) to form a cathode layer.

Example 2: various graphitic carbons and graphitic materials

Several cathode layers were prepared according to the same procedure as used in example 1, but the starting graphite materials were Highly Oriented Pyrolytic Graphite (HOPG) powder, natural graphite powder, pitch-based graphite fibers, vapor grown carbon nanofibers (VG-CNF), and amorphous graphite, respectively.

Example 3: preparation of graphite oxide using a modified Hermes (Hummers) method and subsequent coating of amorphous graphite with graphene oxide sheets

Graphite oxide is prepared by oxidizing natural graphite flakes with sulfuric acid, sodium nitrate and potassium permanganate according to the hermersian method [ U.S. Pat. No. 2,798,878, 7/9/1957 ]. In this example, for every 1 gram of graphite we used a mixture of 22ml of concentrated sulfuric acid, 2.8 grams of potassium permanganate and 0.5 grams of sodium nitrate. Graphite flakes were immersed in the mixture solution and the reaction time at 35 ℃ was approximately 4 hours. It is important to note that potassium permanganate should be added gradually to sulfuric acid in a well-controlled manner to avoid overheating and other safety issues. After the reaction was complete, the sample was then washed repeatedly with deionized water until the pH of the filtrate was about 5. The solution was sonicated for 30 minutes to produce a graphene oxide suspension.

Pouring amorphous graphite powder containing microcrystals into the graphene oxide suspension to form a slurry. The slurry was spray dried to form graphene oxide-encapsulated amorphous graphite particles (protected microparticles). We have observed that the cycle life of the protected amorphous graphite particles (defined as the number of charge/discharge cycles to achieve a 20% capacity reduction) is significantly longer than that of the unprotected amorphous graphite particles (> 3,000 cycles for the protected particles versus <1,000 cycles for the unprotected particles).

Example 4: cathode active layer containing soft carbon particles

Soft carbon particles are prepared from a liquid crystalline aromatic resin. The resin was ground with a mortar and calcined at 900 ℃ for 2h in an N2 atmosphere to prepare graphitizable carbon or soft carbon. The soft carbon particles were then surface treated with a 30% aqueous solution of sulfuric acid at room temperature for 2 hours to remove the hard carbon skin. The rinsed and dried soft carbon particles were then coated with sulfonated PEEK.

Example 5: petroleum pitch derived hard carbon particles

Asphalt samples (A-500 from Ashland Chemical Co., Ltd.) were carbonized at 900 ℃ for 2 hours and then at 1,200 ℃ for 4 hours. In order to remove the carbon coat layer of the pitch-based hard carbon particles, the hard carbon particles were surface-treated with an aqueous KOH solution (5% concentration).

Example 6: intermediate phase carbon

Optically anisotropic spherical carbon (average particle diameter: 25 μm, soluble in quinoline: 5%) was prepared from a coal-based mesophase pitch by heat-treating the pitch at 500 ℃ for 2 hours, carbonizing at 900 ℃ for 2 hours, and then partially graphitizing at 2,500 ℃ for 1 hour. The graphitic carbon particles are then coated with sulfonated polyaniline.

Example 7: multi-walled carbon nanotubes (MW-CNT) of different tube lengths

Powder samples of MW-CNTs (5% by weight) were dispersed with 0.5% by weight surfactant in water to form several suspensions. The suspension was then sonicated for 30 minutes, 1 hour, and 3 hours, respectively. One of the samples (3 hours) was further ball milled in a high intensity mill for 5 hours. The resulting CNT samples had different average CNT lengths (43.5 μm, 3.9 μm, and 0.32 μm, respectively). Some CNTs were protected with carbonized phenolic resin.

Example 8: preparation and testing of various polyvalent Metal ion cells

Particles or fibers of the graphitic carbon materials prepared in examples 1-7 were separately prepared as cathode layers and incorporated into metal-ion secondary batteries. A cathode layer was prepared in the following manner. As an example, first, 95% by weight of graphitic carbon fibers or particles (with or without surface treatment) or paint and PVDF (binder) are mixed together in NMP to obtain a slurry mixture. The slurry mixture is then cast onto a glass surface to produce a wet layer, which is dried to obtain the cathode layer.

Two types of polyvalent metal anodes were prepared. One is a metal foil having a thickness of from 20 to 300 μm. The other is a thin coating of metal deposited on the surface of conductive nanofilaments (e.g., CNTs) or graphene sheets that form an integrated 3D network with electronically conductive pathways of the pores and pore walls for accepting a polyvalent metal or alloy thereof. The metal foil itself or the integrated 3D nanostructures also serve as the anode current collector.

Cyclic Voltammetry (CV) measurements were performed using an Arbin electrochemical workstation at typical scan rates of 0.5-50 mV/s. In addition, the electrochemical performance of each cell was also evaluated by constant current charge/discharge cycling at current densities from 50mA/g to 10A/g. For long-term cycling tests, a multi-channel battery tester manufactured by LAND was used.

Fig. 2 shows the charge and discharge curves of two Zn foil anode based cells: one Zn ion cell contains a cathode layer of pristine graphite fibers and the other Zn ion cell contains a cathode layer of surface treated graphite fibers with the hard carbon skin removed. The discharge curve of the Zn ion cell characterized by skinless graphite fibers exhibited longer plateau states at 1.15-1.35 volts and higher specific capacity (plateau at 150mAh/g and overall capacity of 180mAh/g) relative to the cell with the cathode of the original untreated graphite fibers (plateau at 20mAh/g and overall capacity of 35 mAh/g). The resulting cell level energy density was about 100Wh/kg, higher than that of nickel metal hydride, and very close to that of lithium ion batteries. However, zinc is richer, safer and significantly less expensive than lithium.

Shown in fig. 3 are the discharge curves of two Ca ion cells: one cell contains a cathode layer of Carbon Nanofibers (CNF) without a hard carbon skin (skin that has been chemically etched away), and the other cell contains a cathode layer of CNF with a hard carbon skin. Skinless CNFs enable Ca ion cells to give a discharge curve plateau of up to 80mAh/g, as opposed to only 30mAh/g for cells characterized by untreated CNFs.

fig. 4 shows the discharge curves of two cells based on Ni mesh anodes; one Ni-ion cell contained the cathode layer of the original MCMB particles and the other Ni-ion cell contained the cathode layer of the surface-treated MCMB particles. Also, by removing the hard carbon skin from the graphitic carbon particles, the ion storage capacity can be significantly increased, in this case 105mAh/g versus 52 mAh/g.

Summarized in table 1 below are typical plateau voltage ranges for discharge curves for various polyvalent metal ion cells using skinless artificial graphite, graphite fibers, and CNF as cathode active materials. The specific capacity is typically from 100 to 250 mAh/g. In contrast, for each type of battery cell, the corresponding graphitic carbon with a hard carbon skin provides a very limited ion storage capacity (typically <50 mAh/g).

Table 1: the platform voltage range of the discharge curve in the polyvalent metal ion cell.

Fig. 5 shows the specific capacity of two V-needle coke cells (one V-ion cell containing a sulfonated PVDF protected needle coke cathode and the other V-ion cell containing an unprotected needle coke cathode) plotted as a function of charge/discharge cycle number. These data indicate that the V-ion cell can maintain 90% capacity in 2500 cycles if the needle coke particles are protected by the selected coating. In contrast, V ion cells containing unprotected needle coke suffered a 20% capacity reduction after approximately 1,000 charge/discharge cycles.

Similarly, fig. 6 shows the specific capacities of two Mg ion cells, one containing the cathode layer of MWCNTs protected by carbonized phenolic resin and the other containing the cathode layer of unprotected MWCNTs. The protected versions enable a significantly higher level of cycling stability.

Summarized in fig. 7 are the raleigh plots for two Ti ion cells, one with a cathode having surface treated MCMB and the other with untreated MCMB. The treated MCMB spheres with their hard carbon skin substantially removed enable the Ti ion cells to impart higher energy density and higher power density.

We have also observed that shorter carbon nanotubes or carbon nanofibers, when implemented as cathode active materials, result in higher energy densities and higher power densities.

In addition, we have found that the power density and high rate performance of metal ion cells can be significantly increased by supporting a multivalent metal (in the form of a thin film or coating) on a nanostructured network composed of interconnected carbon or graphite filaments (e.g., carbon nanotubes or graphene sheets). This nanostructured network of interconnected carbon nanofibers provides a large surface area to support multivalent metals and promote rapid and uniform dissolution and deposition of metal cations at the anode side. Other nanofilaments or nanostructures that may be used to make such networks include electrospun nanofibers, vapor grown carbon or graphite nanofibers, carbon or graphite whiskers, carbon nanotubes, metal nanowires, or combinations thereof.