阅读说明：本技术 一种离子电容器负极材料及其制备方法和应用 (Negative electrode material of ionic capacitor and preparation method and application thereof ) 是由 张全生 蒋文苹 闵凡奇 杨旸 孙媛钰 黄之灏 张小展 党国举 于 2020-11-30 设计创作，主要内容包括：本发明涉及一种离子电容器负极材料及其制备方法和应用,制备方法包括以下步骤：(1)将偏磷酸盐与炭基负极材料混匀；再通过固相法进行偏磷酸盐包覆炭基负极材料,制备成活性材料,然后将活性材料与导电剂、粘结剂和集流体混合,制备成负极材料；(2)将负极材料与隔膜、电解液和锂片组装成扣式半电池,以小倍率电流进行金属元素的电化学方法预镶嵌,得到离子电容器负极材料。与现有技术相比,本发明具有可以抑制锂枝晶产生、循环稳定性高、首次库伦效率高、电容器能量密度高等优点。(The invention relates to an ion capacitor cathode material and a preparation method and application thereof, wherein the preparation method comprises the following steps: (1) uniformly mixing metaphosphate with the carbon-based negative electrode material; then, carrying out metaphosphate coating on the carbon-based negative electrode material by a solid phase method to prepare an active material, and then mixing the active material with a conductive agent, a binder and a current collector to prepare a negative electrode material; (2) and assembling the negative electrode material, the diaphragm, the electrolyte and the lithium sheet into a button type half cell, and pre-embedding the button type half cell by a small-rate current electrochemical method of metal elements to obtain the negative electrode material of the ionic capacitor. Compared with the prior art, the lithium ion secondary battery has the advantages of capability of inhibiting the generation of lithium dendrites, high cycle stability, high first coulombic efficiency, high energy density of a capacitor and the like.)

1. A preparation method of an ion capacitor negative electrode material is characterized by comprising the following steps:

(1) uniformly mixing metaphosphate with the carbon-based negative electrode material; then, carrying out metaphosphate coating on the carbon-based negative electrode material by a solid phase method to prepare an active material, and then mixing the active material with a conductive agent, a binder and a current collector to prepare a negative electrode material;

(2) and assembling the negative electrode material, the diaphragm, the electrolyte and the lithium sheet into a button type half cell, and pre-embedding the button type half cell by a small-rate current electrochemical method of metal elements to obtain the negative electrode material of the ionic capacitor.

2. The preparation method of the negative electrode material of the ionic capacitor as claimed in claim 1, wherein the mixing is performed by mixing metaphosphate and carbon-based negative electrode material with ethanol solution and then performing wet mixing in a ball milling or sand milling mode, wherein the ball milling or sand milling time is 2-18 h.

3. The method as claimed in claim 1, wherein the solid phase method comprises heating to 400-800 deg.C at a temperature rise rate of 2-10 deg.C/min under argon atmosphere, calcining for 2-10h, and naturally cooling to room temperature under argon atmosphere.

4. The method for preparing the negative electrode material of the ionic capacitor as claimed in claim 1, wherein the conductive agent is graphene, carbon nanotubes, conductive carbon black, graphite conductive agent, carbon fiber conductive agent;

the binder is polyvinyl alcohol (PVA), Polytetrafluoroethylene (PTFE), sodium carboxymethyl cellulose (CMC), olefin, polyvinylidene fluoride/N-methyl pyrrolidone (PVDF/NMP);

the current collector is an aluminum current collector, a copper current collector, a nickel current collector, a stainless steel current collector, a carbon current collector or a composite current collector;

the electrolyte is an organic solution of lithium salt; the lithium salt is lithium perchlorate, lithium hexafluorophosphate or lithium tetrafluoroborate, and the organic solvent in the electrolyte is propylene carbonate, ethylene carbonate, ethyl carbonate, dimethyl carbonate or methyl ethyl carbonate;

the diaphragm is a Celgard diaphragm or a cellulose paper diaphragm.

5. The method for preparing the negative electrode material of the ionic capacitor as claimed in claim 1, wherein the electrochemical method comprises one-time discharge or three-time cycle charge and discharge;

in the primary discharge: assembling a half cell, wherein the discharge multiplying power is 0.05C, the inlay quantity is 0-250mAh/g, and the discharge cut-off voltage is 0.05V;

in the three times of charge and discharge: the semi-cell is assembled, the charge-discharge multiplying power is 0.05C, and the charge-discharge cut-off voltage is 0.05-3V.

6. The method of claim 1, wherein the metaphosphate comprises one or more of lithium metaphosphate, aluminum metaphosphate, niobium metaphosphate, lanthanum metaphosphate, magnesium metaphosphate, yttrium metaphosphate, or neodymium metaphosphate;

the carbon-based negative electrode material comprises one or more of soft carbon, hard carbon, graphite or mesocarbon microbeads.

7. The method for preparing the negative electrode material of the ionic capacitor as claimed in claim 1, wherein the mass content of the metaphosphate in the negative electrode material is 1-7%.

8. The method for preparing the negative electrode material of the ionic capacitor as claimed in claim 1, wherein the ionic capacitor comprises a lithium ion capacitor, a sodium ion capacitor, a magnesium ion capacitor, an aluminum ion capacitor, a zinc ion capacitor or a calcium ion capacitor.

9. An ion capacitor negative electrode material produced by the method of claims 1-8.

10. Use of the negative electrode material for an ion capacitor according to claim 9, wherein the negative electrode material is assembled with a positive electrode active material, an electrolyte and a separator into an ion capacitor;

the positive active material comprises a porous carbon-based material or a conductive polymer, a conductive agent, a binder and a current collector; the porous carbon-based material is activated carbon fiber, activated carbon powder, carbon nano tube or graphene, or a mixture of one of lithium iron phosphate, lithium manganese iron phosphate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, lithium manganese oxide, lithium nickel cobalt manganese aluminate or lithium cobalt oxide and one of activated carbon fiber, activated carbon powder, carbon nano tube or graphene; the conductive polymer is polyaniline, polyparaphenylene, polypyrrole or polythiophene and derivatives thereof; the conductive agent is graphene, carbon nano tubes, conductive carbon black, a graphite conductive agent and a carbon fiber conductive agent; the binder is polyvinyl alcohol (PVA), Polytetrafluoroethylene (PTFE), sodium carboxymethyl cellulose (CMC), olefin, polyvinylidene fluoride/N-methyl pyrrolidone (PVDF/NMP); the current collector is an aluminum current collector, a copper current collector, a nickel current collector, a stainless steel current collector, a carbon current collector or a composite current collector;

the electrolyte is an organic solution of lithium salt; the lithium salt is lithium perchlorate, lithium hexafluorophosphate or lithium tetrafluoroborate, and the organic solvent in the electrolyte is propylene carbonate, ethylene carbonate, ethyl carbonate, dimethyl carbonate or methyl ethyl carbonate;

the diaphragm is a Celgard diaphragm or a cellulose paper diaphragm.

Technical Field

The invention relates to the field of electrochemistry, and particularly relates to an ion capacitor cathode material, and a preparation method and application thereof.

Background

With the rapid development of economic society, new energy is receiving attention as a strategic emerging industry of the country. As an important support and auxiliary technology of new energy industry, energy storage technology is concerned by all parties. The development of energy storage devices with high energy density and high power density is particularly important in the face of the great requirements of electric automobiles, wind power generation, urban rail transit, power grid equipment, emergency power supplies, heavy trucks, port machinery and the like. A Lithium Ion Capacitor (LIC) is a hybrid Capacitor, and usually stores electric energy in a Lithium-based organic electrolyte system by using the principle of negative electrode electrochemical Lithium intercalation combined with positive electrode charge adsorption.

Compared with the double electric layer capacitor, the total specific capacity and the working voltage of the capacitor are remarkably improved, the energy density is greatly improved while the power characteristic is kept, and the capacitor has the characteristics of high power, long service life, high energy density of a lithium ion battery and the like. Therefore, the method faces to the national important requirements, develops the high-performance lithium ion capacitor and the key preparation technology thereof, solves the key problem in the process of developing the lithium ion capacitor, can provide powerful support for low-carbon economy and social sustainable development, and further improves the innovation capability of the new technology development source in China.

The energy density of a lithium ion capacitor depends mainly on the specific capacitance of the electrode material and the operating voltage of the electrode material in the electrolyte. The electrode material and the electrolyte are the determining factors for determining the performance of the lithium ion capacitor. From the analysis of electrode materials, the energy density of carbon-based lithium ion capacitors, which are mainly activated carbon materials in the prior art, is generally low.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provide an ion capacitor negative electrode material which can inhibit the generation of lithium dendrite, has high cycle stability, high first coulombic efficiency and high capacitor energy density, and a preparation method and application thereof.

The purpose of the invention can be realized by the following technical scheme:

from the analysis of electrode materials, for carbon-based lithium ion capacitors, energy storage through an electric double layer is a physical process of surface adsorption, and no bulk phase atoms participate, so that the energy density of the lithium ion capacitors adopting the activated carbon materials is generally low.

The inventor knows that to improve the energy density of the lithium ion capacitor, the influence of the microstructure, the composition and the distribution of the electrode material on the specific capacitance of the electrode material must be known, the carbon material with the controllable pore structure is prepared by adopting a new process, and the physicochemical property of the carbon material is adjusted by other physical and chemical means.

The pre-embedded lithium is the most important ring in the research and development process of the lithium ion capacitor, the pre-embedded lithium amount is difficult to accurately control by adopting a cut-off voltage limiting method, and a certain safety problem also exists by adopting a mode of directly short-circuiting a negative electrode and a lithium source. Based on the analysis, the invention develops a lithium intercalation technology which can accurately control the lithium intercalation amount and has no safety problem, is the most core and the most key means of the lithium ion capacitor, and has the following specific scheme:

a preparation method of an ion capacitor negative electrode material comprises the following steps:

(1) uniformly mixing metaphosphate with the carbon-based negative electrode material; performing metaphosphate coating on the carbon-based negative electrode material by a solid phase method to prepare an active material so as to finish physical inlaying of metal elements, and then mixing the active material with a conductive agent, a binder and a current collector to prepare a negative electrode material;

(2) and assembling the negative electrode material, the diaphragm, the electrolyte and the lithium sheet into a button type half cell, and pre-embedding the button type half cell by a small-rate current electrochemical method of metal elements to obtain the negative electrode material of the ionic capacitor.

Further, the uniformly mixing is to mix the metaphosphate and the carbon-based negative electrode material by adopting an ethanol solution and then perform wet-method uniformly mixing in a ball milling or sanding mode, wherein the ball milling or sanding time is 2-18 h. Preferably, the mixing is wet ball milling, the ball milling time is 18h, and the rotation speed is 200-350 rpm.

Furthermore, the solid phase method is that under the argon atmosphere, the temperature is raised to 400-800 ℃ at the temperature rise rate of 2-10 ℃/min, the calcination is carried out for 2-10h, and then the natural cooling is carried out to the room temperature under the argon atmosphere. Preferably, the calcination temperature is 600-800 ℃, and the calcination time is 6 h.

Further, the conductive agent is graphene, carbon nanotubes, conductive carbon black: such as acetylene black, SuperP, SuperS, 350G, Ketjen black, graphite conductive agents: such as KS-6, KS-15, SFG-6, SFG-15, carbon fiber-based conductive agents;

the binder is polyvinyl alcohol (PVA), Polytetrafluoroethylene (PTFE), sodium carboxymethyl cellulose (CMC), olefins (PE and other copolymers), polyvinylidene fluoride/N-methyl pyrrolidone (PVDF/NMP);

the current collector is an aluminum current collector (containing carbon-coated aluminum foil), a copper current collector, a nickel current collector, a stainless steel current collector, a carbon current collector or a composite current collector;

the electrolyte is an organic solution of lithium salt; the lithium salt is lithium perchlorate, lithium hexafluorophosphate or lithium tetrafluoroborate, and the organic solvent in the electrolyte is propylene carbonate, ethylene carbonate, ethyl carbonate, dimethyl carbonate or methyl ethyl carbonate;

the diaphragm is a Celgard diaphragm or a cellulose paper diaphragm.

Further, the electrochemical method comprises one-time discharge or three-time cycle charge and discharge;

in the primary discharge: assembling into a half cell, wherein the discharge rate is 0.05C, the mosaic quantity is 0-250mAh/g, preferably 250mAh/g, and the discharge cut-off voltage is 0.05V;

in the three times of charge and discharge: the semi-cell is assembled, the charge-discharge multiplying power is 0.05C, and the charge-discharge cut-off voltage is 0.05-3V.

Further, the metaphosphate comprises one or more of lithium metaphosphate, aluminum metaphosphate, niobium metaphosphate, lanthanum metaphosphate, magnesium metaphosphate, yttrium metaphosphate or neodymium metaphosphate;

the carbon-based negative electrode material comprises one or more of soft carbon, hard carbon, graphite or mesocarbon microbeads.

Further, the mass content of the metaphosphate in the negative electrode material is 1-7%, preferably 3%.

Further, the ionic capacitor comprises a lithium ion capacitor, a sodium ion capacitor, a magnesium ion capacitor, an aluminum ion capacitor, a zinc ion capacitor or a calcium ion capacitor.

The negative electrode material of the ion capacitor manufactured by the method.

The application of the negative electrode material of the ion capacitor, which is assembled with the positive electrode active material, the electrolyte and the diaphragm into the ion capacitor;

the positive active material comprises a porous carbon-based material or a conductive polymer, a conductive agent, a binder and a current collector; the porous carbon-based material is activated carbon fiber, activated carbon powder, carbon nano tube or graphene, or a mixture of one of lithium iron phosphate, lithium manganese iron phosphate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, lithium manganese oxide, lithium nickel cobalt manganese aluminate or lithium cobalt oxide and one of activated carbon fiber, activated carbon powder, carbon nano tube or graphene; the conductive polymer is polyaniline, polyparaphenylene, polypyrrole or polythiophene and derivatives thereof; the conductive agent is graphene, carbon nano tubes and conductive carbon black: such as acetylene black, SuperP, SuperS, 350G, Ketjen black, graphite conductive agents: such as KS-6, KS-15, SFG-6, SFG-15, carbon fiber-based conductive agents; the binder is polyvinyl alcohol (PVA), Polytetrafluoroethylene (PTFE), sodium carboxymethyl cellulose (CMC), olefins (PE and other copolymers), polyvinylidene fluoride/N-methyl pyrrolidone (PVDF/NMP); the current collector is an aluminum current collector (containing carbon-coated aluminum foil), a copper current collector, a nickel current collector, a stainless steel current collector, a carbon current collector or a composite current collector;

the electrolyte is an organic solution of lithium salt; the lithium salt is lithium perchlorate, lithium hexafluorophosphate or lithium tetrafluoroborate, and the organic solvent in the electrolyte is propylene carbonate, ethylene carbonate, ethyl carbonate, dimethyl carbonate or methyl ethyl carbonate;

the diaphragm is a Celgard diaphragm or a cellulose paper diaphragm.

Compared with the prior art, the invention has the following advantages:

(1) according to the invention, metaphosphate is attached to the surface of the carbon-based negative electrode material through physical coating, and a coating layer similar to a glass is formed at high temperature, so that the contact between electrolyte and the carbon-based negative electrode material can be effectively isolated, the occurrence of side reaction is avoided, the generation of lithium dendrite can be inhibited, the lithium insertion amount is increased, and the cycle stability of the lithium insertion amount is improved;

(2) according to the invention, physical coating and electrochemical lithium intercalation are combined, so that the lithium intercalation amount is further increased on the premise of maintaining the original effect, and the improvement of the first coulomb efficiency is realized;

(3) the invention only needs to add a little metaphosphate, has simple preparation method, does not cause high economic cost, further improves the energy density of the lithium ion capacitor, and is a lithium intercalation technology with industrial production potential;

(4) according to the invention, the HC is pre-intercalated with lithium in an electrochemical lithium intercalation mode, and the effect after lithium intercalation in three times of charge and discharge is obviously superior to that after lithium intercalation in one time of discharge by comparing the lithium intercalation in one time with the lithium intercalation in three times; and the lithium intercalation amount and the coulombic efficiency of the hard carbon are improved by combining a physical coating method and a pre-lithium intercalation technology, and the electrochemical lithium intercalation can accurately control the pre-lithiation degree.

Drawings

FIG. 1 is a discharge curve showing different degrees of lithium intercalation in one-time discharge in example 1;

FIG. 2 is a lithium intercalation curve of three-time charge-discharge lithium intercalation in example 2;

FIG. 3 is a first charge-discharge curve of a hard carbon negative electrode to which 0%, 1%, 3%, 5%, 7% lithium metaphosphate was added in examples 1, 3-6;

FIG. 4 is a rate test curve for hard carbon anodes with 0% and 1% lithium metaphosphate added as in example 3;

fig. 5 is a cycle test curve for hard carbon anodes with 0% and 1% lithium metaphosphate added as in example 3;

fig. 6 is a rate test curve for hard carbon anodes with 0% and 3% lithium metaphosphate added as in example 4;

fig. 7 is a cycle test curve for hard carbon anodes with 0% and 3% lithium metaphosphate added as in example 4;

fig. 8 is a rate test curve for hard carbon anodes with 0% and 5% lithium metaphosphate added as in example 5;

fig. 9 is a cycle test curve for hard carbon anodes with 0% and 5% lithium metaphosphate added as in example 5;

fig. 10 is a rate test curve for hard carbon anodes with 0% and 7% lithium metaphosphate added as in example 6;

fig. 11 is a cycle test curve for hard carbon anodes with 0% and 7% lithium metaphosphate added as in example 6;

FIG. 12 is a flow chart of the manufacturing process of the present invention.

Detailed Description

The invention is described in detail below with reference to the figures and specific embodiments.

Example 1

A lithium intercalation method for primary discharge of a lithium ion capacitor is characterized in that the hard carbon is pre-intercalated with lithium by primary discharge through low-rate current (0.05C), the lithium intercalation amount is respectively 0, 100, 150, 200 and 250mAh/g as shown in figure 1, wherein the lithium intercalation termination voltage is 0.05V, and the lithium intercalation process is completed in a button type half cell consisting of a hard carbon cathode, a diaphragm, electrolyte and a lithium piece.

The hard carbon negative electrode comprises a hard carbon active material, a conductive agent Super P, a binder PVDF, a copper current collector and the like, wherein the mass ratio of the active material to the conductive agent to the binder is 90:2:8, and a solvent is NMP; the septum is Celgard septum 2325; the electrolyte contains 1.2M LiPF₆EC: EMC: DMC ═ 1:1:1 organic solvent of the electrolyte.

As can be seen from FIG. 1, the lithium intercalation termination voltage is 0.1029V and still higher than 0.05V when the intercalation is up to 250 mAh/g.

Example 2

A lithium intercalation method for three-time charge and discharge of a lithium ion capacitor is characterized in that three-time cycle charge and discharge are carried out on hard carbon within a lithium intercalation voltage interval of 0.05-3V by small-rate current (0.05C), as shown in figure 2, and the lithium intercalation process is completed in half-buckling electricity consisting of a hard carbon cathode, a diaphragm, electrolyte and a lithium sheet. The third lithium intercalation amount is 231.5 mAh/g.

The hard carbon negative electrode comprises a hard carbon active material, a conductive agent Super P, a binder PVDF, a copper current collector and the like, wherein the mass ratio of the active material to the conductive agent to the binder is 90:2:8, and a solvent is NMP; the septum is Celgard 2325; the electrolyte contains 1.2M LiPF₆EC: EMC: DMC ═ 1:1:1 organic solvent of the electrolyte.

Compared with the embodiment 1, the lithium intercalation effect after three times of charge and discharge is obviously better than that of the lithium intercalation effect after one time of discharge. Therefore, in the subsequent examples, lithium intercalation behavior after coating is studied in the form of lithium intercalation by three-time charging and discharging.

Example 3

A method of lithium insertion for a lithium ion capacitor, the method comprising the steps of:

(1) uniformly mixing 1% of lithium metaphosphate and hard carbon in a ball milling mode, wherein a ball milling solvent is absolute ethyl alcohol, the ball milling time is 18 hours, and the ball milling rotating speed is 350 rpm. And then placing the uniformly mixed composite material in a tubular furnace, taking argon as a calcining atmosphere, raising the temperature to 600 ℃ at the temperature rise rate of 2 ℃/min, keeping the temperature for 6 hours, naturally cooling to room temperature, and taking out the calcined material.

(2) The lithium intercalation process is finally completed in a button type half cell consisting of a hard carbon cathode, a diaphragm, electrolyte and a lithium sheet by carrying out three times of cyclic charge and discharge on the hard carbon coated with 1% of lithium metaphosphate within a lithium intercalation voltage interval of 0.05-3V by virtue of a small rate current (0.05C). The hard carbon negative electrode comprises 1% of lithium metaphosphate coated hard carbon, a conductive agent Super P, a binder PVDF, a copper current collector and the like, wherein the mass ratio of an active material to the conductive agent to the binder is 90:2:8, and a solvent is NMP; the septum is Celgard 2325; the electrolyte contains 1.2M LiPF₆EC: EMC: DMC ═ 1:1:1 organic solvent of the electrolyte.

Then assembling the pole pieces after lithium intercalation into a full-buckling type lithium ion capacitor, wherein the lithium intercalation pole piece is taken as a negative electrode, the activated carbon is taken as a positive electrode and the LiPF is contained₆In EC, the DMC is 1:1:1 as electrolyte, and Celgard2325 as diaphragm; the active carbon anode comprises an active carbon material, a conductive agent Super P, a binder PTFE, an aluminum current collector and the like, wherein the mass ratio of the active material to the conductive agent to the binder is 90:2:8, and the solvent is NMP.

Compared with the example 2, the lithium insertion amount of the hard carbon can be improved by adding 1% of lithium metaphosphate as shown in figure 3, and the lithium insertion amount is 496.1 mAh/g; as shown in fig. 4, the rate discharge capacity is comparable to that of the original hard carbon; as shown in fig. 5, the capacity retention rate after 100 cycles at a charge-discharge rate of 1C was 91.6%, which is greater than 88.72% of the original hard carbon. In summary, the electrochemical performance of the lithium ion capacitor can be improved by combining physical coating and electrochemical lithium intercalation.

Example 4

A method of lithium insertion for a lithium ion capacitor, the method comprising the steps of:

(1) uniformly mixing 3% of lithium metaphosphate and hard carbon in a ball milling mode, wherein a ball milling solvent is absolute ethyl alcohol, the ball milling time is 18 hours, and the ball milling rotating speed is 350 rpm. And then placing the uniformly mixed composite material in a tubular furnace, taking argon as a calcining atmosphere, raising the temperature to 600 ℃ at the temperature rise rate of 2 ℃/min, keeping the temperature for 6 hours, naturally cooling to room temperature, and taking out the calcined material.

(2) The lithium intercalation process is completed in half-charging consisting of a hard carbon cathode, a diaphragm, electrolyte and a lithium sheet by performing three-time cyclic charge and discharge on 3% lithium metaphosphate coated hard carbon within a lithium intercalation voltage interval of 0.05-3V through a small-rate current (0.05C). The hard carbon negative electrode comprises 3% of lithium metaphosphate coated hard carbon, a conductive agent Super P, a binder PVDF, a copper current collector and the like, the mass ratio of an active material to the conductive agent to the binder is 90:2:8, and a solvent is NMP; the septum is Celgard 2325; the electrolyte contains 1.2M LiPF₆EC: EMC: DMC ═ 1:1:1 organic solvent of the electrolyte.

Then, assembling the pole piece after lithium intercalation into a full-buckling type lithium ion capacitor, wherein the lithium intercalation pole piece is used as a negative electrode, and activated carbon is used as the active carbonIs a positive electrode and contains LiPF₆In EC, the DMC is 1:1:1 as electrolyte, and Celgard2325 as diaphragm; the active carbon anode comprises an active carbon material, a conductive agent Super P, a binder PTFE, an aluminum current collector and the like, wherein the mass ratio of the active material to the conductive agent to the binder is 90:2:8, and the solvent is NMP.

Compared with the examples 2-3, as shown in FIG. 3, the addition of 3% of lithium metaphosphate can increase the lithium insertion amount of the hard carbon, and the lithium insertion amount is 515.3 mAh/g; as shown in fig. 6, the rate discharge capacity is superior to that of the original hard carbon; as shown in fig. 7, after 100 cycles of cycling at a rate of 1C, the capacity retention rate is 96.9%, which is greater than 88.72% of the original hard carbon, and the electrochemical performance of the lithium ion capacitor can be improved by combining physical coating and electrochemical lithium intercalation. In summary, the effect by adding 3% lithium metaphosphate is better than 1%.

Example 5

A method of lithium insertion for a lithium ion capacitor, the method comprising the steps of:

(1) uniformly mixing 5% of lithium metaphosphate and hard carbon in a ball milling mode, wherein a ball milling solvent is absolute ethyl alcohol, the ball milling time is 18 hours, and the ball milling rotating speed is 350 rpm. And then placing the uniformly mixed composite material in a tubular furnace, taking argon as a calcining atmosphere, raising the temperature to 600 ℃ at the temperature rise rate of 2 ℃/min, keeping the temperature for 6 hours, naturally cooling to room temperature, and taking out the calcined material.

(2) The lithium intercalation process is completed in half-charging consisting of a hard carbon cathode, a diaphragm, electrolyte and a lithium sheet by performing three-time cyclic charge and discharge on 5% lithium metaphosphate coated hard carbon within a lithium intercalation voltage interval of 0.05-3V through a small-rate current (0.05C). The hard carbon negative electrode comprises 5% of lithium metaphosphate coated hard carbon, a conductive agent Super P, a binder PVDF, a copper current collector and the like, the mass ratio of an active material to the conductive agent to the binder is 90:2:8, and a solvent is NMP; the diaphragm is Celgard 2325; the electrolyte contains 1.2M LiPF₆An organic solvent having an electrolyte EC of EMC: DMC of 1:1: 1;

then assembling the pole pieces after lithium intercalation into a full-buckling type lithium ion capacitor, wherein the lithium intercalation pole piece is taken as a negative electrode, the activated carbon is taken as a positive electrode and the LiPF is contained₆In EC, DMC is 1:1:1 as electrolyte, Celgard2325 isA diaphragm; the active carbon anode comprises an active carbon material, a conductive agent Super P, a binder PTFE, an aluminum current collector and the like, wherein the mass ratio of the active material to the conductive agent to the binder is 90:2:8, and the solvent is NMP.

Compared with the embodiment 2 and the embodiment 4, the lithium inserting amount is 450.6mAh/g after 5 percent of lithium metaphosphate in the figure 3; as shown in fig. 8, the rate discharge capacity is lower than that of the original hard carbon; as shown in fig. 9, after 100 cycles of cycling at a rate of 1C, the capacity retention rate is 91.5%, which is greater than 88.72% of the original hard carbon, and the electrochemical performance of the lithium ion capacitor can be improved by combining physical coating and electrochemical lithium intercalation. In summary, the effect by adding 3% lithium metaphosphate is better than 5%, which may be caused by excessive addition of lithium metaphosphate.

Example 6

A method of lithium insertion for a lithium ion capacitor, the method comprising the steps of:

(1) uniformly mixing 7% of lithium metaphosphate and hard carbon in a ball milling mode, wherein a ball milling solvent is absolute ethyl alcohol, the ball milling time is 18 hours, and the ball milling rotating speed is 350 rpm. And then placing the uniformly mixed composite material in a tubular furnace, taking argon as a calcining atmosphere, raising the temperature to 600 ℃ at the temperature rise rate of 2 ℃/min, keeping the temperature for 6 hours, naturally cooling to room temperature, and taking out the calcined material.

(2) The lithium intercalation process is completed in half-charging consisting of a hard carbon cathode, a diaphragm, electrolyte and a lithium sheet by carrying out three-time cyclic charge and discharge on 7% lithium metaphosphate coated hard carbon within a lithium intercalation voltage interval of 0.05-3V by small-rate current (0.05C). The hard carbon negative electrode comprises 7% of hard carbon coated by lithium metaphosphate, a conductive agent Super P, a binder PVDF, a copper current collector and the like, the mass ratio of an active material to the conductive agent to the binder is 90:2:8, and a solvent is NMP; the septum is Celgard 2325; the electrolyte contains 1.2M LiPF₆EC: EMC: DMC ═ 1:1:1 organic solvent of the electrolyte.

Then assembling the pole pieces after lithium intercalation into a full-buckling type lithium ion capacitor, wherein the lithium intercalation pole piece is taken as a negative electrode, the activated carbon is taken as a positive electrode and the LiPF is contained₆In EC, the DMC is 1:1:1 as electrolyte, and Celgard2325 as diaphragm; wherein the active carbon positive electrode contains activeThe carbon material, the conductive agent Super P, the adhesive PTFE, the aluminum current collector and the like, wherein the mass ratio of the active material to the conductive agent to the adhesive is 90:2:8, and the solvent is NMP.

Compared with the embodiment 2 and the embodiment 4, as shown in the figure 3, after 7 percent of lithium metaphosphate, the lithium inserting amount is 327.9 mAh/g; as shown in fig. 10, the rate discharge capacity is lower than that of the original hard carbon; as shown in fig. 11, after 100 cycles of cycling at a rate of 1C, the capacity retention rate is 88.9%, which is greater than 88.72% of the original hard carbon, and the electrochemical performance of the lithium ion capacitor can be improved by combining physical coating and electrochemical lithium intercalation. In summary, the effect by adding 3% lithium metaphosphate is better than that of 7%, which may be caused by excessive addition of lithium metaphosphate.

The foregoing is directed to preferred embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow. However, any simple modification, equivalent change and modification of the above embodiments according to the technical essence of the present invention are within the protection scope of the technical solution of the present invention.