Nonaqueous electrolyte composition
阅读说明：本技术 非水电解质组合物 (Nonaqueous electrolyte composition ) 是由 J·巴克 R·塞耶斯 于 2018-12-13 设计创作，主要内容包括：本发明涉及新的非水电解质组合物,其包含：a)通式为NaMF<Sub>x</Sub>的含钠化合物,和b)溶剂体系,其包含第一溶剂组分i)和第二溶剂组分ii),所述第一溶剂组分i)包含碳酸异丙烯酯和一种或多种另外的含有机碳酸酯的溶剂,所述第二溶剂组分ii)包含一种或多种乙二醇二醚和/或一种或多种乙二醇醚乙酸酯；其中碳酸异丙烯酯：一种或多种乙二醇二醚和/或一种或多种乙二醇醚乙酸酯的摩尔比的范围为1:0.1至1:3。(The present invention relates to a novel nonaqueous electrolyte composition comprising: a) the general formula is NaMF x And b) a solvent system comprising a first solvent component i) comprising propylene carbonate and one or more additional organic carbonate-containing solvents, and a second solvent component ii) comprising one or more ethylene glycol diethers and/or one or more ethylene glycol ether acetates; wherein propylene carbonate: one or more glycolsThe diether and/or the one or more glycol ether acetates are in a molar ratio ranging from 1:0.1 to 1: 3.)
1. A nonaqueous electrolyte composition comprising:
a) one or more of the general formula of NaMFxWherein M is one or more metals and/or non-metals, and x is 4 or 6; and
b) a solvent system comprising:
i) a first solvent component comprising propylene carbonate and one or more additional organic carbonate-based solvents; and
ii) a second solvent component comprising one or more ethylene glycol diethers and/or one or more ethylene glycol ether acetates;
wherein propylene carbonate: the molar ratio of the one or more ethylene glycol diethers and/or the one or more ethylene glycol ether acetates ranges from 1:0.1 to 1: 3.
2. The nonaqueous electrolyte composition according to claim 1, wherein M is selected from aluminum (Al)3+) Boron (B)3+) Gallium (Ga)3+) Indium (In)3 +) Scandium (Sc)3+) Yttrium (Y)3+) Lanthanum (L a)3+) Phosphorus (P)5+) And arsenic (As)5+)。
3. The non-aqueous electrolyte composition according to claim 1, wherein the one or more additional organic carbonate based solvents are selected from one or more of diethyl carbonate, dimethyl carbonate, ethylene carbonate and ethyl methyl carbonate.
4. The non-aqueous electrolyte composition according to claim 1, wherein the second solvent component ii) comprises one or more ethylene oxide based glymes and/or one or more propylene oxide based glymes.
5. The non-aqueous electrolyte composition according to claim 1, wherein the second solvent component ii) comprises one or more polyethylene glycol diethers selected from one or more of diglyme, triglyme and tetraglyme.
6. The non-aqueous electrolyte composition according to claim 1, wherein a) comprises one or more additional sodium salts selected from the group consisting of formula NaXO and sulfone-containing compounds4The compound of (1).
7. The non-aqueous electrolyte composition according to claim 1, wherein the solvent system b) comprises a third solvent component iii) comprising one or more sulfone group-containing solvents.
8. The nonaqueous electrolyte composition according to any one of claims 1 to 7, which is selected from the group consisting of: 0.5M NaPF in a solvent mixture containing ethylene carbonate, diethyl carbonate, propylene carbonate and glyme in a ratio of 2:4:2:16(ii) a And 0.5M NaBF in a solvent mixture containing ethylene carbonate, diethyl carbonate, propylene carbonate and glyme in a ratio of 1:2:1:14。
9. A sodium ion battery comprising a negative electrode, a positive electrode and the nonaqueous electrolyte composition according to any one of claims 1 to 8.
10. The sodium ion battery of claim 9, wherein the negative electrode comprises a modified graphitic carbon material.
11. The sodium ion battery of claim 9, wherein the negative electrode comprises hard carbon.
12. The sodium ion battery of any one of claims 9-11, further comprising one or more electrolyte additives.
13. An energy storage device comprising a negative electrode, a positive electrode, and the nonaqueous electrolyte composition according to any one of claims 1 to 8.
14. The energy storage device of claim 13, selected from the group consisting of a battery, a rechargeable battery, an electrochemical device, and an electrochromic device.
Technical Field
The present invention relates to a novel nonaqueous electrolyte composition, a sodium ion battery comprising the novel nonaqueous electrolyte composition, and an energy storage device such as a battery, a rechargeable battery, an electrochemical device, and an electrochromic device comprising the nonaqueous electrolyte composition.
Background
Sodium ion batteries are similar in many respects to the lithium ion batteries in widespread use today; they are all reusable secondary batteries comprising an anode (negative electrode), a cathode (positive electrode) and an electrolyte material, all capable of storing energy, and all charge and discharge through similar reaction mechanisms. When the sodium ion (or lithium ion) battery is charged, Na+(or L i+) Ions are extracted from the cathode and inserted into the anode. At the same time, charge balancing electrons travel from the cathode through the external circuit containing the charger and into the anode of the cell. During discharge, the same process occurs, but in the opposite direction.
In recent years, lithium ion battery technology has received much attention and provides the preferred portable battery for most electronic devices in use today. However, lithium is not an inexpensive metal source and is considered too expensive for use in large scale applications. In contrast, sodium ion battery technology is still in its relative infancy, but is considered to be advantageous; sodium is much more abundant than lithium and some researchers predict that this will provide a cheaper and more durable way to store energy for the future, especially for large scale applications such as storing energy on the grid. However, there is much work to be done before sodium ion batteries become commercially viable.
One area in which much attention is needed is the development of suitable electrolyte compositions, particularly for sodium ion batteries.
While the design of suitable electrolyte compositions places less attention than active materials (electrodes), their importance should not be overlooked, as they are largely critical to battery life and performance in determining the actual performance achievable by the battery, e.g., capacity, rate capability, safety, etc. However, to be a suitable electrolyte composition, it must satisfy a long range of properties, including:
chemical stability-the battery must not react during operation, including within the electrolyte itself or with the separator, electrode, current collector or packaging material used;
electrochemical stability-high and low initial potentials must have a large separation for decomposition by oxidation or reduction, respectively;
thermal stability-the electrolyte composition needs to be liquid and therefore its melting and boiling points must be outside the internal operating temperature of the battery. Electrolyte solvent systems are particularly important for this property.
Ionic conductivity and electronic insulation, respectively for passage of Na+Transmission is necessary to maintain battery operation and minimize battery self-discharge;
low toxicity;
based on sustainable chemistry, i.e. using abundant elements and produced by low impact synthesis (energy, pollution, etc.);
cost-effective preparation.
In lithium ion batteries, the most common electrolyte composition contains L iPF dissolved in an organic carbonate based solvent6Or L iBF4Most workers believe that 1M L iPF is included in the EC (ethylene carbonate)/DMC (dimethyl carbonate) mixture or EC (ethylene carbonate)/EMC (ethyl methyl carbonate) mixture6The electrolyte composition of (a) is a "standard" lithium ion battery electrolyte. In the case of sodium ion batteries, the sodium analog NaPF can be used6Substitute L iPF6A more cost effective alternative, however, is NaBF4. The latter also having a chemical bond with NaPF6Compared to the advantage of improved thermal stability. Unfortunately, however, NaBF4The solubility in organic carbonate based electrolyte solvents is very low, which results in ion conductivity of the resulting electrolyte composition being generally too low for practical use. Therefore, when NaPF is used6When compared with an equivalent battery, contains NaBF4The poor solubility of the electrolyte compositions in conventional organic carbonate-based solvents yieldsPoor electrochemical performance results.
In order to overcome the solubility problem of organic carbonate groups, attempts have been made to develop NaBF4Solvents for the electrolyte compositions that are more readily soluble therein. For example, m.egashira et al, in Electrochimica Acta, volume 58, 12/30/2011, pages 95-98: the ionic conductivity of a ternary electrolyte containing sodium salt and ionic liquid (ionic conductivity of tertiary electrolytes and ionic liquid) is described, and NaBF is contained4The nonaqueous electrolyte of (1) may effectively contain a mixture of the following solvents: i) a high level of tetraglyme material, namely poly (ethylene glycol) dimethyl ether (PEGDME), and ii) ionic liquid diethylmethoxyethyl ammonium tetrafluoroborate (DEMEBF)4)。PEGDME:NaBF4:DEMEBF4Is disclosed as being 8:1: 2.
Indeed, many Ionic liquids meet many requirements for providing suitable electrolyte solvents, they are liquids over a wide range, they exhibit Thermal and electrical Stability, and they have no or very low vapor pressure, which makes them nonflammable and therefore very Safe, e.g., f.wu et al in "Highly Safe Ionic liquid Electrolytes for Sodium Ion batteries: wide electrochemical Window and Good Thermal Stability (high safety Ionic L iquid Electrolytes for Sodium Ion batteries)", ACS application.material. interfacess, 2016, 21381-21386. despite these advantages Ionic liquids have some significant drawbacks, firstly, most Ionic liquids have quite high viscosities, generally of the order of magnitude above, and furthermore, when the Ionic liquids have a very poor charge, often show a few tens of charge, they are often not considered to be expensive to be used in situ for batteries.
Ki-Won Kim et al in Materials Research Bulletin 58(2014)74-77, "electrolyte pair Na/a-NaMnO2Effect of The electrochemical Performance of The cell (The effect of electrochemical on The electrochemical properties of Na/a-NaMnO)2Batteries) "and A.Rudola et al in The Journal of The Electrochemical Society,164(6) A1098-A1109(2017)," monoclinic Sodium Hexacyanoferrate Iron Cathode and nonflammable Glyme-based electrolyte for Inexpensive Sodium Ion Batteries (monoclinicSodium Iron Hexacyanoboth Cathode and Non-ferromagnetic glass-base electrolyte for Inesponsive Sodium Batteries) "further work showed that when used in poly (ethylene glycol) dimethyl ether (PEGDME, tetraglyme) containing 1M NABF, The electrolyte was used4The electrolyte of (3) was tested against a graphite anode to obtain electrochemical results. However, as demonstrated by Rudola et al, in sodium ion batteries with graphite anodes, pure tetraglyme electrolyte exhibited a battery capacity significantly lower than that of carbonate-based electrolytes; with the use of a carbonate-based electrolyte (1M NaClO in EC: PC)4) Has a measured capacity of 170.9mAh/g compared to that of a positive electrode active material having 1M NaBF in tetraglyme4The cell of (2) showed 35mAh/[ g (anode) + g (cathode)]And low (about 90%) coulomb efficiency. The reason that carbonate electrolytes impart higher capacity performance is due in part to the stability of carbonate electrolytes over a wider voltage range, while pure tetraglyme-based electrolytes are limited in this regard. However, pure carbonate electrolytes cannot be used for all-sodium ion batteries with graphite because propylene carbonate (propylene carbonate) solvent can be intercalated into graphite, causing mechanical damage to the material and hindering electrochemical performance.
Disclosure of Invention
It is therefore an object of the present invention to provide improved sodium ion conducting electrolyte compositions (i.e. they are electrolyte compositions designed for sodium ion secondary batteries) using a NaMF of the general formula dissolved in a suitable solvent systemxWith x ═ 4 or 6, for example sodium tetrafluoroborate (NaBF)4) And sodium hexafluorophosphate (NaPF)6). The electrolyte compositions of the present invention will be cost effective and will not suffer from the above-mentioned disadvantages of standard organic carbonate solvent systems and solvent systems comprising large amounts of ionic liquids. Furthermore, the present invention aims to provide electrolyte compositions that exhibit excellent electrochemical performance in sodium ion batteries, particularly in sodium ion batteries employing non-graphitic carbon anode electrodes, such as hard carbon anode electrodes.
The present invention accomplishes these objectives by providing a new solvent system that comprises a carefully selected combination of solvents.
Accordingly, the present invention provides a nonaqueous electrolyte composition comprising:
a) one or more of the general formula of NaMFxWherein M is one or more metals and/or non-metals, and x is 4 or 6; and
b) a solvent system comprising:
i) a first solvent component comprising propylene carbonate (an organic carbonate based solvent) and one or more additional organic carbonate based solvents; and
ii) a second solvent component comprising one or more ethylene glycol diethers and/or one or more ethylene glycol ether acetates;
wherein the molar ratio of propylene carbonate to one or more ethylene glycol diethers and/or one or more ethylene glycol ether acetates is in the range of 1:0.1 to 1: 3.
As demonstrated in the specific examples presented below, the above-described solvent systems of the present invention provide surprising and significant advantages (particularly with respect to reduced first cycle losses) over other solvent systems that do not specifically comprise propylene carbonate in addition to one or more additional organic carbonate based solvents and one or more ethylene glycol diethers and/or ethylene glycol ether acetates.
The metal or metals and/or non-metals M are preferably selected from aluminium (Al)3+) Boron (B)3+) Gallium (Ga)3+) Indium (In)3+) Scandium (Sc)3+) Yttrium (Y)3+) Lanthanum (a)La3+) And phosphorus (P)5+). Particularly preferably, M is selected from (Al)3+) Boron (B)3+) Gallium (Ga)3+) Phosphorus (P)5+) And arsenic (As)5+). The most preferred formula is NaMFxThe sodium-containing salt of (A) is sodium tetrafluoroborate (NaBF)4) And sodium hexafluorophosphate (NaPF)6)。
In a preferred non-aqueous electrolyte composition of the invention, a) is a compound of formula NaMF, except for one or more of the abovexIn addition to the sodium-containing salt of (a), one or more additional sodium salts may also be present.
The one or more additional sodium salts can be any suitable sodium salt. They are preferably selected from:
NaXO of formula4Wherein X is one or more halogens, such as fluorine, chlorine, bromine and iodine. Preferred additional sodium salts include NaClO4；
Sodium triflate, also known as sodium triflate or NaOTf (CF)6NaSO3)；
Sodium bis (fluorosulfonyl) imide, also known as NaFSI (NaN (SO)2F)2) (ii) a And
sodium bis (trifluoromethanesulfonyl) imide, also known as NaTFSI (C)2F6NNaO4S2)
The electrolyte compositions of the present invention may further comprise a third solvent component iii) comprising one or more solvents containing sulfone groups, for example of the general formula R-SO2-a solvent for R'. In these sulfone group-containing solvents, R and R' may be independently selected (i.e., they may be the same or different from each other) from any straight or branched, substituted or unsubstituted C1To C6Alkyl groups (e.g. tetramethylsulphone-ethyl acetate (TMS-EA)), or any substituted or unsubstituted C1To C6A meta alkyl or alkenyl ring such as a cyclic sulfone. A preferred cyclic sulfone is (CH)2)4SO2It is known as sulfolane.
Accordingly, the present invention provides a nonaqueous electrolyte composition comprising:
a) one or more of the general formula of NaMFxThe sodium-containing salt of (1), whichWherein M is one or more metals and/or non-metals as defined above, and x is 4 or 6; and optionally one or more additional sodium salts as defined above; and
b) a solvent system comprising:
i) a first solvent component comprising propylene carbonate and one or more additional organic carbonate-based solvents;
ii) a second solvent component comprising one or more ethylene glycol diethers and/or one or more ethylene glycol ether acetates; and
iii) a third solvent component comprising one or more sulfone group-containing solvents.
It is convenient to express the amount of propylene carbonate in terms of molar ratio relative to the amount of one or more ethylene glycol diethers and/or one or more ethylene glycol ether acetates (collectively referred to herein as "glyme"). The molar ratio of Propylene Carbonate (PC) to glyme is preferably in the range of 1:0.1 to 1:3, more preferably in the range of 1:0.1 to 1:2, and particularly preferably in the range of 1:0.2 to 1: 2. Particularly preferred is a molar ratio of PC to glyme in the range of 1:0.5 to 1: 1.5.
It is also convenient to define the molar ratio of the amount of glyme present in the solvent system relative to the total amount of organic carbonate-containing compound present, i.e. propylene carbonate, and one or more additional organic carbonate-based solvents, such that the preferred molar ratio of total amount of organic carbonate-based solvent to glyme is in the range of 2:1 to 10:1, and further preferred molar ratio is in the range of 4:1 to 8: 1.
The molar ratio of the amount of the one or more additional organic carbonate-based solvents to propylene carbonate is preferably in the range of 6:1 to 1:1, particularly preferably 3: 1.
The present invention differs from the electrolyte compositions described in literature articles by Egashira et al, Ki-Won Kim et al and a. rudola et al, since none of these prior art documents teach electrolyte compositions containing propylene carbonate and one or more additional organic carbonate based solvents. Specifically, Rudola et al disclose a composition comprising 1M pure tetraglymeNaBF of (1)4And Egashira et al describe a NaBF contained in a mixture of poly (ethylene glycol) dimethyl ether (PEGDME, polyglycolyme) and an ionic liquid4The electrolyte composition of (1); the molar ratio of the polyglyme to the ionic liquid is 8:0 to 8: 8.
When the solvent system b) comprises the third solvent component iii), the molar ratio of (i + ii): iii (i.e. expressed as the ratio of the number of moles of i) plus the number of moles of ii) to the number of moles of iii) will be in the range of 1:0.25 to 1:5, preferably in the range of 1:0.25 to 1:3, further preferably in the range of 1:0.5 to 1:3, ideally in the range of 1:0.5 to 1:1, and most preferably in the range of 1:0.5 to 1: 2. The amount (i + ii) is determined by the ratio of the number of moles of i) and ii) as described above. For the avoidance of doubt, the third solvent component iii) does not increase the amount of ethylene glycol diether and/or ethylene glycol ether acetate material present in the solvent system.
One or more of the electrolyte compositions of the present invention expressed as NaMFxOne convenient way of determining the amount of sodium-containing compound of (a) is based on the molar concentration of the component in a) in the solvent system b). I.e.per liter of solvent system b), a) of the formula NaMFxIs calculated with the amount of optional additional sodium salt(s), if used. Preferably, the molar concentration of the component in a) ranges from 0.1M to 5M, further preferably ranges from 0.1M to 2M. Very preferably, when the component in a) is NaBF4Or NaPF6When used, the molar concentration is in the range of 0.1M to 2M. The following are under the limits of the ranges of the first solvent component i) and the second solvent component ii), respectively, of the general formula NaMFxOf (e.g., NaBF)4) Calculation of molar concentration in tetraglyme:
0.1M NaBF in carbonate glyme (2:1)4Corresponding to 0.11M NaBF in tetraglyme4The molar concentration of (c).
0.1M NaBF in carbonate glyme (10:1)4Equivalent to 0.10M NaBF in tetraglyme4The molar concentration of (c).
5M NaBF in carbonate glyme (1:2)4Corresponding to 5.04M NaBF in tetraglyme4The molar concentration of (c).
5M NaBF in carbonate glyme (10:1)4Corresponding to 5M NaBF in tetraglyme4The molar concentration of (c).
The ethylene glycol diethers (also called "glymes") used in solvent component ii) are saturated polyethers which contain no other functional groups and they can be prepared using ethylene glycol ether precursor materials. They differ from glycols such as polyethylene glycol (PEG) in that they do not carry free hydroxyl groups and are therefore aprotic polar and chemically inert compounds. There are two main types of ethylene glycol diethers (glymes), depending on whether they are Ethylene Oxide (EO) -based glymes ("e series", also known as PEG-based materials) or Propylene Oxide (PO) -based glymes ("p series", also known as polypropylene glycol (PPG) groups).
Examples of suitable glymes include:
ethylene glycol dimethyl ether (monoglyme CH)3-O-CH2CH2-O-CH3)
Diethylene glycol dimethyl ether (diethylene glycol dimethyl ether CH)3-O-(CH2-O)2-CH3)
Triethylene glycol dimethyl ether (triethylene glycol dimethyl ether, CH)3-O-(CH2-O)3-CH3)
Tetraglyme (tetraglyme, CH)3-O-(CH2-O)4-CH3)
Ethylene glycol diethyl ether (ethyl glyme, CH)3CH2-O-CH2CH2-O-CH2CH3)
Diethylene glycol diethyl ether (ethyl diglyme, CH)3CH2-O-(CH2-O)2-CH2CH3)
Diethylene glycol dibutyl ether (butyl diglycol dimethyl ether, CH)3CH2CH2-O-(CH2-O)2-CH2CH3)
Poly (ethylene glycol) dimethyl ether (polyglycolemethyl ether, CH)3-O-(CH2-O)n-CH3)
Dipropylene glycol dimethyl ether (Proglyme, CH)3-O-(CH2CHCH3-O)2-CH3)
Most ethylene glycol diethers (glymes) benefit from being water soluble, biodegradable, and exhibit low to moderate acute toxicity, and are therefore widely used in industrial applications such as cleaning products, inks, adhesives and coatings, batteries and electronics, absorption refrigeration and heat pumps, and pharmaceutical formulations. Mixtures of methanol or trifluoroethanol with tetraglyme (PEG-DME250) can be used as the working fluid for absorption chillers, while triglyme and tetraglyme, when mixed with refrigerants such as HFC-134a, are lubricants for automotive air conditioning (a/C) compressor units.
As defined above, solvent component ii) may comprise one or more glycol ether acetates in the presence or absence of one or more ethylene glycol diethers (glymes) as defined above. Suitable glycol ether acetates include:
propylene glycol methyl ether acetate,
the propylene glycol methyl ether acetate is added into the solvent,
ethylene glycol monobutyl ether acetate, a mixture of ethylene glycol monobutyl ether acetate,
ethylene glycol monomethyl ether acetate,
ethylene glycol monoethyl ether acetate, and the like,
the content of the diethylene glycol monobutyl ether acetate,
diethylene glycol monoethyl ether acetate, and
diethylene glycol monoethyl ether acetate.
Most preferred are ethylene glycol monomethyl ether acetate and ethylene glycol monoethyl ether acetate.
In the electrolyte compositions of the present invention, it is most preferred to use one or more e-series glymes, i.e., ethylene glycol diethers. It is particularly preferable to use one or more selected from the group consisting of diethylene glycol dimethyl ether (diglyme), triethylene glycol dimethyl ether (triglyme), and tetraethylene glycol dimethyl ether (tetraglyme).
Cyclic organic carbonate propylene Carbonate (CH)3C2H3O2CO) shows good compatibility with electrode materials, it has high solubility and has a high boiling point, which make it advantageous for use in batteries. The one or more additional organic carbonate-based solvents used in the solvent component comprise in their structure a carbonate group, i.e. a carbonyl group flanked by one or two alkoxy groups: r1O(C＝O)OR2And R is1And R2Independently selected from (i.e. they may be the same or different from each other) H and C1To C20A linear or cyclic, branched or unbranched, substituted or unsubstituted alkyl or alkenyl group. C3-C10Cyclic additional organic carbonate based solvents, in particular ethylene carbonate, are very suitable additional solvents. Polyalkylene carbonate materials such as diethyl carbonate, dimethyl carbonate and ethyl methyl carbonate are also very useful.
Preferably, the solvent system of the electrolyte composition of the present invention does not contain any amount of ionic liquid. If an ionic liquid is present in the electrolyte composition of the invention, the amount of the ionic liquid will ensure that the ratio of the first and second solvent components and the ratio of PC to glyme remain within the ratios described above.
In order to produce a functional electrolyte, it is common practice to include additives in the electrolyte composition. An additive is needed to compensate for the disadvantages of the original electrolyte formulation and it is a new chemical with very small addition levels. The small amount of need arises from the preferred action taking place at the electrolyte-electrode interface rather than in the bulk of the electrolyte. Degradation reactions often occur in the case of liquid electrolytes, which result in the adhesion of insoluble products to the surface of the negative electrode and the formation of a protective solid passivation layer, i.e., a Solid Electrolyte Interface (SEI). The typical interfacial/surface effect of the additive is to modify the SEI, increase surface wettability and prevent overcharge events. The additives may also be used as flame retardants, flowability enhancers/viscosity reducers, as well as impurities or free radical scavengers, and the like. Additives particularly useful in the electrolyte compositions of the present invention include one or more additives selected from the group consisting of fluoroethylene carbonate (FEC) and Vinylene Carbonate (VC). Thus, the electrolyte compositions of the present invention comprise a small amount of one or more additional electrolyte additives, e.g. < 5 wt% of the total electrolyte composition.
The electrolyte composition of the present invention is preferably used for sodium ion batteries. Accordingly, in a further embodiment, the present invention provides a sodium ion battery comprising a negative electrode, a positive electrode and an electrolyte composition according to the present invention as described above. Such sodium ion batteries can be used in energy storage devices, such as batteries, rechargeable batteries, electrochemical devices, and electrochromic devices.
Ideally, the electrolyte composition of the present invention is used in a sodium ion battery using a carbon-based negative (anode) electrode.
Carbon in the form of graphite has been favored for some time as an anode material for lithium ion batteries due to its high weight and volumetric capacity, graphite electrodes providing reversible capacities in excess of 360mAh/g, comparable to the theoretical capacity of 372mAh/g+Interpositioned with van der waals gaps between graphene layers to produce L iC6. Although the electrolyte compositions of the present invention may be used with graphite anodes, graphite is in fact much less electrochemically active towards sodium, and this, combined with the fact that sodium has a significantly larger atomic radius than lithium, results in intercalation between graphene layers in graphite anodes being severely limited in sodium ion batteries.
The terms "graphite", "graphitic carbon", "natural graphite" and "synthetic graphite" refer to carbon materials having the typical ordered and layered graphitic structure of graphite found in nature, which have two-dimensional long-range order in both the "a" and "c" crystallographic directions, orientations and divisions. Synthetic graphite is typically prepared by high temperature calcination of a suitable carbon precursor, while natural graphite is excavated from the ground and acid-washed. Specifically, natural graphite and synthetic graphite are defined by the degree of crystallinity and interlayer spacing present; a. the b and c directions are defined by crystallography, have directions, orientations, and divisions, and the interlayer spacing of both natural graphite and synthetic graphite is defined as 3.35 angstroms. Carbon materials that do not exhibit both of these characteristics are not classified as "natural graphite" or "synthetic graphite" or "graphitic carbon".
In contrast, the sodium-ion battery anode of the present invention uses a "modified graphite" carbon material having a more disordered structure than graphite, which allows some of the intercalation problems encountered with sodium ions to be overcome.
Modified graphitic carbon materials include, but are not limited to, non-graphitic carbon, isotropic carbon, partially graphitic carbon, exfoliated graphite, expanded graphite, amorphous carbon, soft carbon, and hard carbon materials. For the avoidance of doubt, "modified graphitic carbon" as used herein does not include any carbon having a natural graphitic structure or synthetic graphitic material having the same structure as a natural graphitic material. The exact structure of the modified graphitic carbon material remains to be solved, but most examples (except the exfoliated and expanded graphite materials discussed below) are characterized by having a two-dimensional long-range order in the "a" crystallographic direction, but unlike natural or synthetic graphites they lack the "c" crystallographic direction, orientation and division. At the same time, all examples of modified graphitic carbon (except soft graphite) are non-graphitizable (i.e. cannot be converted to well-ordered layered structures similar to natural graphite). However, all examples have layers without exception, although the layers are not stacked neatly, and they all have micropores (micron-sized pores) formed between the carbon layers stacked disorderly. Furthermore, all forms of modified graphitic carbon are isotropic on a macroscopic level. One of the reasons why it is difficult to construct a general structural model of the modified graphitic carbon material is that the detailed structure, domain size, proportion of carbon layers, and micropores depend on the synthesis conditions, such as carbon source and carbonization temperature. A typical method of preparing modified graphitic carbon uses a starting material such as sucrose, glucose, petroleum coke or pitch coke, which is mixed with a thermoplastic binder such as coal tar, petroleum-based pitch or synthetic resins and then heated to about 1200 ℃. The "hard carbon material" has layers, but the layers are not stacked neatly, and it has micropores (micron-sized pores) formed between the carbon layers stacked randomly. On a macroscopic level, hard carbon is isotropic. In generalHard carbons suitable for use in the anode may be prepared from carbonaceous starting materials such as sucrose, corn starch, glucose, organic polymers (such as polyacrylonitrile or resorcinol-formaldehyde gel), cellulose, petroleum coke or pitch coke, first mixed with a thermoplastic binder such as coal tar, petroleum-based pitch or synthetic resins and then heated to about 1200 ℃. Commercially available hard carbons include those sold under the trademark CarbotronTMHard carbon material (Kureha Corporation) or Bio-CarbotronTMHard carbon materials (those sold by Kuraray Chemical Company and Kureha Corporation).
Desirably, the sodium ion battery of the present invention uses the carbon material as the anode alone or in combination with one or more other materials such as a metal or nonmetal as described above in the form of a sodium-storable metal or alloy or element or compound thereof, or as a composite material with one or more other materials such as a sodium-storable metal or alloy or element or compound thereof as described above. Particularly preferred anode active materials include hard carbon/X composites, wherein X is one or more selected from phosphorus, sulfur, indium, antimony, tin, lead, iron, manganese, molybdenum and germanium, in elemental form or in compound form, preferably with one or more selected from oxygen, carbon, nitrogen, phosphorus, sulfur, silicon, fluorine, chlorine, bromine and iodine. X is preferably selected from P, S, Sn, SnO2、Sb、Sb2O3One or more of SnSb and SbO.
The modified graphitic carbon material, known as "expanded" or "exfoliated" graphite, has a structure that is identifiable as similar to, but not identical to, that of natural graphite because it is modified such that its carbon exhibits an interlayer spacing in the (001) direction of greater than 3.35 angstroms.
Most preferably, the non-aqueous electrolyte composition of the present invention is used with an anode comprising a modified graphitic carbon, preferably a hard carbon anode.
Accordingly, in a highly preferred embodiment, the present invention provides the above-described nonaqueous electrolyte composition, which is suitable for use in a sodium ion battery containing an anode comprising a modified graphitic carbon material, preferably a hard carbon anode.
Containing carbon secondarilyThe material may also be mixed with the above-mentioned anode active material, such as, inter alia: activated carbon materials, particulate carbon black materials, graphene, carbon nanotubes, and graphite are used in combination to improve the conductivity of the anode. Examples of particulate carbon black materials include: "C65TMCarbon (also known as Super P)TMCarbon Black) (BET Nitrogen surface area 62m2Per g) (available from Timcal L approved), although BET nitrogen surface area is also available<900m2Other carbon blacks/g, e.g. "Ensaco 350gTM", it is a BET nitrogen surface area of 770m2Carbon black per gram (available as specialty Carbon for rubber compositions from Imerys Graphite and Carbon L), BET nitrogen surface area of Carbon nanotubes of 100-1000m2(iv)/g, the BET nitrogen surface area of the graphene is about 2630m2Per g, and a BET nitrogen surface area of the activated carbon material of>3000m2/g。
Furthermore, the present invention provides a sodium ion battery comprising a negative electrode, a positive electrode and the non-aqueous electrolyte composition according to the present invention as described above, wherein the negative electrode comprises a modified graphitic carbon material, preferably a hard carbon material. Such sodium ion batteries can be used in energy storage devices, such as batteries, rechargeable batteries, electrochemical devices, and electrochromic devices.
The sodium ion secondary battery according to the present invention may contain any positive electrode active material. Preferably, the cathode active material will have the general formula:
A1±M1 VM2 WM3 XM4 YM5 ZO2-C
wherein
A is one or more alkali metals selected from sodium, potassium and lithium;
M1comprising one or more redox active metals having an oxidation state of +2, preferably selected from the group consisting of nickel, copper, cobalt and manganese;
M2a metal comprising an oxidation state greater than 0 to greater than or equal to + 4;
M3a metal comprising oxidation state + 2;
M4comprises an oxidation state of more than 0 to less than or equal to +4;
M5a metal comprising oxidation state + 3;
wherein
0≤≤1；
V is > 0;
w is more than or equal to 0;
x is more than or equal to 0;
y is more than or equal to 0;
at least one of W and Y is > O
Z is more than or equal to 0;
c is in the range of 0-2
Wherein V, W, X, Y, Z and C are selected to maintain electrochemical neutrality.
Ideally, the metal M2Comprising one or more transition metals, and preferably selected from manganese, titanium and zirconium; m3Preferably one or more selected from magnesium, calcium, copper, tin, zinc and cobalt; m4Comprising one or more transition metals, preferably selected from manganese, titanium and zirconium; and M5Preferably one or more selected from the group consisting of aluminium, iron, cobalt, tin, molybdenum, chromium, vanadium, scandium and yttrium.
A particularly preferred cathode active material will be a nickelate-based material.
A cathode active material having any crystal structure may be used, however, preferably the structure will be O3 or P2 or derivatives thereof, but in particular the cathode material may also comprise a mixture of phases, i.e. it will have a heterogeneous structure consisting of several different crystal forms.