Graphite material applied to field of lithium batteries, preparation method therefor, and use thereof

Abstract

Provided are a graphite material applied to the field of lithium batteries, and a preparation method therefor. The single-electron defect concentration of the graphite material is less than 10-3 spins / C atom. Additionally, further provided is a lithium ion battery using the graphite material as a negative electrode, wherein the lithium ion battery comprises a positive electrode, a negative electrode, an electrolyte solution, and a separator. The electrolyte solution comprises a lithium salt solution, wherein the concentration of the lithium salt solution is 0.8-1.2 mol / L, solvents of the lithium salt solution comprise a first solvent and a second solvent, the volume fraction of the first solvent is 30-100%, the volume fraction of the second solvent is 0-70%, the first solvent is propylene carbonate or an ether solvent, and the second solvent comprises ethylene carbonate, diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate. The graphite material as a negative electrode of a lithium ion battery can be effectively compatible with propylene carbonate and ether solvents, thereby mitigating the reduction of the service life of the lithium ion battery caused by an intercalation effect of an electrolyte solution, and improving the low-temperature working performance of the lithium ion battery.

Description

Graphite material applied to lithium battery field and preparation method and application thereof TECHNICAL FIELD

[0001] The present disclosure relates to the technical field of lithium ion batteries, in particular to a graphite material applied to the lithium battery field and a preparation method and application thereof. BACKGROUND

[0002] Lithium ion batteries are currently developing rapidly, with increasing production and wide application in mobile electronic devices, electric vehicles and energy storage fields. With technological progress, their energy density is continuously improving, while the cost is gradually decreasing. In the future, lithium ion batteries will play a greater role in new energy power generation and green low-carbon development, helping the global economy and society to achieve green low-carbon transformation.

[0003] Graphite is the most important negative material in lithium ion batteries, accounting for more than 98% of the market share of lithium battery negative materials. The important challenge faced by graphite negative is the irreversible destruction of graphite structure caused by the co-intercalation of some solvents with excellent low-temperature performance and the decomposition of solvent molecules in the micro-intercalation process during the cycle, resulting in a decrease in cycle stability. For example, propylene carbonate (PC, hereinafter referred to as PC-based electrolyte solvent) and ether solvents. PC-based electrolyte solvents are a class of electrolyte solvents with excellent low-temperature properties (melting point of about-48.8℃) and high-pressure resistance, but in the working of lithium ion batteries, PC-based electrolyte solvents will continuously co-intercalate and decompose at the graphite negative, causing the graphite layer to peel off, thereby irreversibly destroying the structure of lithium ion batteries, resulting in the failure of lithium ion batteries. In addition, low-melting-point ether solvents 1,2-dimethoxyethane (DME) and 1,3-dioxolane (DOL) also exhibit solvent co-intercalation due to their strong solvation ability. Therefore, a single PC-based electrolyte solvent or ether electrolyte solvent cannot be used as an electrolyte compatible with graphite negative materials.

[0004] The introduction of ethylene carbonate (EC, hereinafter referred to as EC-based electrolyte solvent) electrolyte promotes the formation of a stable solid-state electrolyte interface (SEI) at the graphite negative, realizing the stable operation of lithium ion batteries. However, during the charging and discharging process of the graphite negative, the co-intercalation of EC-based electrolyte solvents still occurs, which causes the peeling off of the graphite layer boundary and the continuous decomposition of the electrolyte, the gradual thickening of the solid-state electrolyte interface, and a decrease in cycle stability. Moreover, the properties of the EC-based electrolyte solvent, such as high melting point (36.4℃), high viscosity and low oxidation stability, limit the low-temperature ion transport ability of the electrolyte, resulting in a decrease in the low-temperature performance of lithium ion batteries and failing to meet the application requirements in the field of electric vehicles.

[0005] SUMMARY

[0006] Therefore, to solve at least one of the problems in the related art and other problems, the present disclosure provides a graphite material applied to the field of lithium batteries, wherein the single electron defect concentration of the graphite material is less than 10 -3 spins / C atom.

[0007] According to an embodiment of the present disclosure, the g-factor of the graphite material measured by electron paramagnetic resonance spectroscopy is in the range of 2.004-2.008.

[0008] In another aspect of the present disclosure, a preparation method of the graphite material with low electron defects is also provided, comprising: mixing and heating the graphite and an alkali metal conversion agent under a protective atmosphere, and obtaining the graphite material with low electron defects after water washing. The alkali metal conversion agent includes any one of an alkali metal element, an alkali metal nitrogen compound and an alkali metal sulfide; and the single electron defect concentration of the graphite material with low electron defects is less than 10 -3 spins / C atom.

[0009] According to an embodiment of the present disclosure, the heating temperature is 200-800℃, and the heating time is 0.2h-30h.

[0010] According to an embodiment of the present disclosure, the mass fraction of the alkali metal conversion agent accounts for 0.1-10wt% of the total mass of the graphite and the alkali metal conversion agent.

[0011] According to an embodiment of the present disclosure, the alkali metal element includes at least one of lithium, sodium and potassium; the alkali metal nitrogen compound includes at least one of lithium phosphide, sodium phosphide, potassium phosphide, lithium nitride, sodium nitride, potassium nitride, lithium arsenide, sodium arsenide and potassium arsenide; and the alkali metal sulfide includes at least one of lithium sulfide, sodium sulfide and potassium sulfide.

[0012] In another aspect of the present disclosure, a lithium ion battery is also provided, wherein the lithium ion battery includes a positive electrode, a negative electrode, an electrolyte and a separator. The negative electrode material is the graphite material, and the single electron defect concentration of the graphite material is less than 10 -3 spins / C atom; the electrolyte includes a lithium salt solution, wherein the concentration of the lithium salt solution is 0.8-1.2mol / L, the solvent of the lithium salt solution includes a first solvent and a second solvent, the volume fraction of the first solvent is 30-100%, the volume fraction of the second solvent is 0-70%, the first solvent includes at least one of propylene carbonate, 1,2-dimethoxyethane and 1,3-dioxolane, and the second solvent includes at least one of ethylene carbonate, diethyl carbonate, dimethyl carbonate and methyl ethyl carbonate.

[0013] According to an embodiment of the present disclosure, the lithium salt comprises at least one of lithium hexafluorophosphate, lithium bisfluorosulfonimide, lithium difluoro(oxalato)borate, lithium tetrafluoroborate and lithium perchlorate.

[0014] According to an embodiment of the present disclosure, the electrolyte further comprises an additive in a mass fraction of 0.1wt%-10wt%; the additive comprises at least one of fluoroethylene carbonate, difluoroethylene carbonate, vinylene carbonate and phosphite.

[0015] In another aspect of the present disclosure, the application of the aforementioned lithium ion battery in a low-temperature environment is also proposed, wherein the temperature range of the low-temperature environment is -40°C to 0°C.

[0016] According to an embodiment of the present disclosure, when the single electron defect concentration of the graphite material is reduced to 10 -3 spins / C atom, and applied to the lithium battery field, the problem of co-intercalation with low-temperature electrolyte solvent molecules can be effectively solved, the cycle stability of the graphite negative electrode is significantly improved, and it is of great significance to improve the long cycle life, high-pressure resistance and low-temperature performance of the lithium ion battery. BRIEF DESCRIPTION OF DRAWINGS

[0017] FIG. 1 is an electron paramagnetic resonance spectrum of a graphite material in Example 1 of the present disclosure;

[0018] FIG. 2 is a charge-discharge cycle test graph of a graphite half-cell in an EC-based electrolyte solvent in Example 1 of the present disclosure;

[0019] FIG. 3 is a charge-discharge curve of a graphite full cell in a PC-based electrolyte solvent at different temperatures in Example 1 of the present disclosure;

[0020] FIG. 4 is a charge-discharge curve graph of a graphite half-cell in an ether-based electrolyte in Example 1 of the present disclosure;

[0021] FIG. 5 is an electron paramagnetic resonance spectrum of a graphite material in Example 2 of the present disclosure;

[0022] FIG. 6 is a charge-discharge cycle test graph of a graphite half-cell in an EC-based electrolyte solvent in Example 2 of the present disclosure;

[0023] FIG. 7 is an electron paramagnetic resonance spectrum of a graphite material in Example 3 of the present disclosure;

[0024] FIG. 8 is an electron paramagnetic resonance spectrum of a commercialized graphite in Comparative Example 1 of the present disclosure;

[0025] FIG. 9 is a charge-discharge cycle test graph of a graphite half-cell in an EC-based electrolyte solvent in Comparative Example 1 of the present disclosure;

[0026] FIG. 10 is a charge-discharge curve of a graphite full cell in a PC-based electrolyte solvent at room temperature in Comparative Example 1 of the present disclosure;

[0027] Figure 11 is a charge-discharge curve of a graphite half-cell in an ether-based electrolyte in Comparative Example 1 of the present disclosure;

[0028] Figure 12 is an electron paramagnetic resonance spectrum of a graphite material in Comparative Example 2 of the present disclosure;

[0029] Figure 13 is a charge-discharge cycling test graph of a graphite half-cell in an EC-based electrolyte solvent in Comparative Example 2 of the present disclosure. DETAILED DESCRIPTION

[0030] In order to make the objectives, technical solutions, and advantages of the present disclosure clearer, the present disclosure will be described in further detail below with reference to specific embodiments and with reference to the accompanying drawings.

[0031] The endpoints of the ranges and any values disclosed in the present disclosure are not limited to the precise values stated. The ranges or values should be construed to be approximations that allow for significant variation. Various ranges of values that are stated in the specification encompass minimum and maximum values, and also every numerical value between the minimum and maximum values. The endpoints of the ranges and any values are provided as a separate matter from the scope of the range. The range of values includes every value between the minimum and maximum values. For values having only a lower limit, the range of values includes every value greater than the lower limit up to, and including, the upper limit. For values having only an upper limit, the range of values includes every value less than the upper limit down to, and including, the lower limit. For values having both a lower limit and an upper limit, the range of values includes every value between the lower limit and the upper limit.

[0032] The terminology used herein is for the purpose of describing specific embodiments only and is not intended to be limiting of the present disclosure. As used herein, the term "including" "comprising" and the like are specifically intended to be construed to be inclusive of other features, steps, operations, and / or components, but are not limited to only those features, steps, operations, and / or components.

[0033] All terms used herein including technical and scientific terms have the meanings commonly understood by one of ordinary skill in the art unless otherwise defined. It should be noted that the terms used herein are defined as having meanings that are consistent with the context of the specification, and should not be interpreted in an idealized or overly formal way.

[0034] It should be noted that, unless otherwise defined, the technical terms or scientific terms used in the present disclosure should be the common meanings understood by those skilled in the art to which the present disclosure belongs. If the terms "first", "second", and the like are used in the entire text, the "first", "second", and the like are only used to distinguish similar objects, and cannot be understood as indicating or implying the relative importance, the order of precedence, or implicitly indicating the number of the technical features indicated. It should be understood that the data of "first", "second", and the like can be interchanged under appropriate circumstances.

[0035] Similarly, to simplify the present disclosure and help understand one or more of the various disclosed aspects, in the above description of exemplary embodiments of the present disclosure, various features of the present disclosure are sometimes grouped together in a single embodiment, figure, or description thereof. Reference to a term "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" etc. means that a particular feature, structure, material or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present disclosure. Illustrative expressions of the above terms in the specification do not necessarily refer to the same embodiment or example. Moreover, the described particular features, structures, materials, or characteristics can be combined in any suitable manner in one or more embodiments or examples.

[0036] In addition, the technical solutions of various embodiments can be combined with each other, but it must be based on the fact that a person skilled in the art can realize it. When the combination of technical solutions contradicts each other or cannot be realized, it should be considered that the combination of technical solutions does not exist and is not within the protection scope required by the present application.

[0037] PC-based electrolyte solvent is considered to be an ideal low-temperature electrolyte solvent with a low melting point of -48.8°C and a high dielectric constant of 64.9, but a single PC-based electrolyte solvent is not compatible with a graphite negative electrode. The graphite negative electrode will undergo a severe solvent intercalation reaction in the PC-based electrolyte solvent, causing the graphite layer to peel off and unable to cycle normally, so it is difficult to form a battery. In related technologies, the strategy to solve the compatibility of PC-based electrolyte solvent and graphite negative electrode is mainly to form a stable solid electrolyte interface on the surface of the graphite negative electrode, such as introducing additives, solvents or using high-concentration electrolyte to adjust the solvation structure of lithium ions and then promote the desolvation process of PC and lithium ions.

[0038] Due to reasons such as crystal structure, preparation process and physical properties, graphite materials inevitably have a large number of electronic defects. It is found in the implementation of the present disclosure that low-electronic-defect graphite materials can improve the cycle stability of the graphite negative electrode and the compatibility with the electrolyte when used as a lithium ion battery negative electrode, especially PC-based electrolyte solvent, limit the intercalation effect of the electrolyte, and improve the cycle and low-temperature performance of the lithium ion battery.

[0039] Further, the present disclosure finds that co-heating a conventional graphite material with an alkali metal material can effectively improve the electronic defect concentration of the graphite material, which can be effectively adapted to PC-based electrolyte and the like when used as a lithium ion battery negative electrode, reduce solvent intercalation during charging and discharging, and be applied in low-temperature environments.

[0040] The present disclosure proposes a graphite material applied in the field of lithium batteries, wherein the single-electron defect concentration of the graphite material is less than 10 -3 spins / C atom.

[0041] According to an embodiment of the present disclosure, when the single electron defect concentration of the graphite material is reduced to 10 -3 spins / C atom, and applied to the lithium battery field, the problem of co-intercalation with low-temperature electrolyte solvent molecules can be effectively solved, and the cycle stability of the graphite negative electrode is significantly improved, which is of great significance to improve the long cycle life, charge cut-off voltage and low-temperature performance of the lithium ion battery.

[0042] According to an embodiment of the present disclosure, the g-factor of the graphite material measured by electron paramagnetic resonance spectrum (EPR) ranges from 2.004 to 2.008.

[0043] According to an embodiment of the present disclosure, the single electron defect concentration of the graphite material is calculated by measuring the g-factor in the electron paramagnetic resonance spectrum of the graphite material.

[0044] In another aspect of the present disclosure, a preparation method of a low-electron-defect graphite material is also provided, which comprises: mixing and heating the graphite and an alkali metal conversion agent under a protective atmosphere, and obtaining the low-electron-defect graphite material after water washing. The alkali metal conversion agent comprises any one of an alkali metal element, an alkali metal nitrogen compound and an alkali metal sulfide; and the single electron defect concentration of the low-electron-defect graphite material is less than 10 -3 spins / C atom.

[0045] According to an embodiment of the present disclosure, the alkali metal element, the alkali metal nitrogen compound and the alkali metal sulfide have the ability to provide electrons, and when they are co-heated with the graphite material having a large number of single electron defects as the conversion agent, the electrons will be injected into the graphite material to repair the electron defects at the boundaries of the graphite material, thereby obtaining the graphite material with low electron defects. At the same time, the alkali metal conversion agent can be removed by water washing, thereby obtaining a single pure graphite material. Different from the method of introducing other elements to modify the graphite material to reduce the electron defects of the graphite material in the related art, the preparation method of the low-electron-defect graphite material proposed in the present disclosure can obtain a pure graphite material on the one hand, and ensure the stability of the graphite material itself, and on the other hand, reduce the electron defect concentration of the graphite material, and improve the conductivity and carrier mobility of the graphite material in the actual application process.

[0046] According to an embodiment of the present disclosure, the protective atmosphere comprises an inert gas atmosphere such as nitrogen or argon.

[0047] According to an embodiment of the present disclosure, the heating temperature is 200-800℃, for example, it can be 200℃, 400℃, 600℃, 800℃, etc., and preferably 500℃; and the heating time is 0.2h-30h, for example, it can be 0.2h, 1h, 5h, 10h, 15h, 20h, 25h, 30h, etc.

[0048] According to an embodiment of the present disclosure, the temperature of heating can affect the graphitization degree of the graphite material, thereby affecting the electron defect concentration of the graphite material. Meanwhile, the heating temperature and the heating time are negatively correlated in the range, and a relatively low heating temperature requires a relatively long heating time to achieve electron injection of the alkali metal nitride or sulfide into the graphite material.

[0049] According to an embodiment of the present disclosure, the mass fraction of the alkali metal conversion agent is 0.1-10wt% of the total mass of the graphite and the alkali metal conversion agent, for example, can be 0.1wt%, 1wt%, 2wt%, 4wt%, 6wt%, 8wt%, 10wt%, etc.

[0050] According to an embodiment of the present disclosure, the alkali metal element includes at least one of lithium, sodium, and potassium; the alkali metal nitride includes at least one of lithium phosphide, sodium phosphide, potassium phosphide, lithium nitride, sodium nitride, potassium nitride, lithium arsenide, sodium arsenide, and potassium arsenide; and the alkali metal sulfide includes at least one of lithium sulfide, sodium sulfide, and potassium sulfide.

[0051] According to an embodiment of the present disclosure, the alkali metal material itself has excellent electron-donating ability, and in the alkali metal nitride and sulfide, the nitrogen group and sulfur have high electron deficiency, so that the electrons possessed by the alkali metal can be better extracted, and the electrons can be injected to the graphite electron defect position under the condition of heating.

[0052] In another aspect of the present disclosure, a lithium ion battery is also disclosed, wherein the lithium ion battery includes a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode material is a graphite material, and the single electron defect concentration of the graphite material is less than 10 -3 spins / C atom; the electrolyte includes a lithium salt solution, wherein the concentration of the lithium salt solution is 0.8-1.2mol / L, for example, can be 0.8mol / L, 0.9mol / L, 1.0mol / L, 1.1mol / L, 1.2mol / L, etc., the solvent of the lithium salt solution includes a first solvent and a second solvent, the volume fraction of the first solvent is 30-100%, and the volume fraction of the second solvent is 0-70%, the first solvent includes at least one of propylene carbonate (PC), 1,2-dimethoxyethane (DME), and 1,3-dioxolane (DOL), and the second solvent includes at least one of ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and methyl ethyl carbonate (EMC).

[0053] In some specific embodiments, the components of the first solvent and the second solvent can be: a single first solvent, i.e., the volume fraction of the first solvent is 100%; or the volume fraction of the first solvent is 90% and the volume fraction of the second solvent is 10%; or the volume fraction of the first solvent is 80% and the volume fraction of the second solvent is 20%; or the volume fraction of the first solvent is 70% and the volume fraction of the second solvent is 30%; or the volume fraction of the first solvent is 60% and the volume fraction of the second solvent is 40%; or the volume fraction of the first solvent is 50% and the volume fraction of the second solvent is 50%; or the volume fraction of the first solvent is 40% and the volume fraction of the second solvent is 60%; or the volume fraction of the first solvent is 30% and the volume fraction of the second solvent is 70%; and the like. The higher the volume fraction of the first solvent, the more suitable the lithium ion battery is for a low-temperature environment.

[0054] According to embodiments of the present disclosure, the present disclosure proposes a new lithium ion battery system, which uses a graphite material with a low single electron defect concentration as a negative electrode, is conducive to the desolvation process of solvated lithium ions at the graphite boundary, effectively inhibits the insertion of solvents in the electrolyte into the graphite layer, and improves the cycle stability of the lithium ion battery. At the same time, the present disclosure also finds that maintaining the structure of the graphite negative electrode can not only ensure good cycle stability when using a low-temperature electrolyte including only a first solvent and a lithium salt, but also greatly improve the capacity retention rate, cycle performance, and cut-off voltage of the battery at low temperatures; and can also improve the cycle life when a second solvent is added, and the addition of the second solution can weaken the intercalation ability of the electrolyte.

[0055] According to embodiments of the present disclosure, in related technologies, propylene carbonate has poor compatibility with the graphite negative electrode, and ether organic solvents are active and have poor oxidation resistance, so the first solvent is difficult to be used alone as the electrolyte solvent of the lithium ion battery; and ethylene carbonate (EC) has high chemical stability, but has a high melting point and is difficult to be used as the electrolyte of the lithium ion battery in a low-temperature environment. The present disclosure solves the damage of the co-intercalation solvent to the graphite by adjusting the graphite negative electrode, so that a single first solvent can constitute the lithium ion battery system as the electrolyte solvent, simplifies the composition of the electrolyte, and realizes the low-temperature stability and cycle stability of the lithium ion battery.

[0056] According to embodiments of the present disclosure, the lithium salt includes at least one of lithium hexafluorophosphate, lithium bisfluorosulfonimide, lithium difluoro(oxalato)borate, lithium tetrafluoroborate, and lithium perchlorate.

[0057] According to an embodiment of the present disclosure, the electrolyte further comprises an additive in a mass fraction of 0.1wt%-10wt%, which can be optionally 1wt%, 2wt%, 4wt%, 6wt%, 8wt%, 10wt%, etc., and preferably in a mass fraction of 0.1wt%-5wt%; the additive comprises at least one of fluoroethylene carbonate, difluoroethylene carbonate, vinylene carbonate, phosphite, etc.

[0058] According to an embodiment of the present disclosure, the additive functions to form a film structure on the surface of the graphite negative electrode to reduce electrolyte solvent intercalation, protect the graphite negative electrode, prevent battery overcharging, prevent fire and explosion, and prolong the service life of the lithium ion battery.

[0059] According to an embodiment of the present disclosure, in the related art, a large amount of additive is usually required in the electrolyte of the lithium ion battery to achieve the effects of negative electrode film formation, overcharge protection, fire and explosion prevention, and to improve low-temperature performance, such as carboxylic acid ester (methyl propionate, ethyl acetate, methyl acetate, etc.), boron-containing additive (tetramethyl borate, trimethyl borate), phosphate additive (triallyl phosphate), etc. However, in the present disclosure, the optimization of the negative electrode material can achieve the above effects without the addition of additive or with the addition of a small amount (less than 10wt%) of additive.

[0060] In another aspect of the present disclosure, the use of the aforementioned lithium ion battery in a low-temperature environment is also disclosed, wherein the temperature range of the low-temperature environment is -40°C to 0°C.

[0061] According to an embodiment of the present disclosure, thanks to the application of the graphite negative electrode with low electron defect concentration and the PC-based electrolyte, the lithium ion battery inherently has good low-temperature and high-voltage resistance characteristics. Thus, no electrolyte additive for improving low-temperature performance and high-voltage resistance performance is required in the electrolyte, thereby reducing the additive components in the electrolyte and providing a wider adjustment range for the full battery design. It can be found through tests that the graphite negative electrode material with low electron defect characteristics proposed in the present disclosure can achieve better low-temperature performance in the PC-based electrolyte solvent than in the EC-based electrolyte solvent, can maintain more than 62% of the room temperature capacity in an environment of -40°C, and has no lithium precipitation in long-term cycling. It is also found in the present disclosure that the charging cutoff voltage of such lithium ion battery is increased by 0.1-0.2V compared with the lithium ion battery in the prior art, and is more suitable for high charging cutoff voltage environment.

[0062] It should be noted that the described embodiments are only part of the embodiments of the present disclosure, rather than all the embodiments. Based on the embodiments in the present disclosure, other embodiments obtained by those of ordinary skill in the art without creative labor are within the scope of protection of the present disclosure.

[0063] Embodiment 1

[0064] Under an argon-filled atmosphere, lithium phosphide and graphite powder were mixed uniformly at a mass ratio of 50 mg:500 mg, heat-treated at 500°C for 1 hour, and after natural cooling, the low-electron-defect graphite material was obtained after water washing, filtration, and drying.

[0065] The graphite material prepared in Example 1 was analyzed by electron paramagnetic resonance.

[0066] FIG. 1 is an electron paramagnetic resonance spectrum of the graphite material in Example 1 of the present disclosure.

[0067] As shown in FIG. 1, the graphite material g-factor prepared in Example 1 was 2.004, and the electron defect concentration value was calculated to be 8.84 x 10 -5 .

[0068] The low-electron-defect graphite material prepared in Example 1 was assembled into a half-cell for testing.

[0069] FIG. 2 is a charge-discharge cycle test diagram of the graphite half-cell in Example 1 of the present disclosure in an EC-based electrolyte solvent.

[0070] In the first test, the electrolyte composition was vinyl carbonate (EC), lithium hexafluorophosphate, and diethyl carbonate (DEC) (1M LiPF6+ EC:DEC = 1:1 (volume ratio)). At a current density of 0.1C, the reversible capacity of the battery was 359.4 mAhg -1 , as shown in FIG. 2, the capacity retention rate was 90% after 300 cycles at a current density of 0.5C.

[0071] FIG. 3 is a charge-discharge curve of the graphite full cell in Example 1 of the present disclosure at different temperatures in a PC-based electrolyte solvent.

[0072] In the second test, the electrolyte composition was propylene carbonate (PC), lithium hexafluorophosphate, and diethyl carbonate (DEC) (1M LiPF6+ PC:DEC = 1:1 (volume ratio)), and the reversible capacity was 359.8 mAhg -1 . The graphite material prepared in Example 1 was assembled with NCM523 positive electrodes to form a full cell with a surface capacity of 2.04 mAhcm -2 , and the charge-discharge interval was 2.8-4.3V, as shown in FIG. 3, the reversible capacity was 1.27 mAhcm -2 at -40°C (capacity retention rate was 62%).

[0073] FIG. 4 is a charge-discharge curve of the graphite half-cell in Example 1 of the present disclosure in an ether-based electrolyte.

[0074] In the third test, the electrolyte was composed of lithium bis-trifluoromethanesulfonimide, 1,3-dioxolane and 1,2-dimethoxyethane (DME) (1M LiTFSI+DOL:DME=1:1 (volume ratio)), as shown in FIG. 4, which had a reversible capacity of 208.2 mAhg at a current density of 0.1C -1 .

[0075] Example 2

[0076] Under an argon-filled atmosphere, lithium sulfide was mixed with graphite powder at a mass ratio of 20mg:400mg, and heat-treated at 400°C for 5 hours. After natural cooling, the low-electron-defect graphite material was obtained after water washing, filtration and drying.

[0077] The graphite sample prepared in Example 2 was analyzed by electron paramagnetic resonance.

[0078] FIG. 5 is an electron paramagnetic resonance spectrum of the graphite material in Example 2 of the present disclosure.

[0079] As shown in FIG. 5, the graphite material g-factor prepared in Example 2 was 2.008, and the electron defect concentration value was calculated to be 1.93x10 -4 .

[0080] The low-electron-defect graphite material prepared in Example 2 was assembled into a half-cell for testing.

[0081] FIG. 6 is a charge-discharge cycle test diagram of the graphite half-cell in Example 2 of the present disclosure in an EC-based electrolyte solvent.

[0082] In the test, the electrolyte was composed of ethylene carbonate (EC), lithium hexafluorophosphate and diethyl carbonate (DEC) (1M LiPF6+EC:DEC=1:1 (volume ratio)), which had a reversible capacity of 359.1 mAhg at a current density of 0.1C -1 As shown in FIG. 6, the capacity retention rate was 87% after 300 cycles at a current density of 0.5C.

[0083] Example 3

[0084] Under an argon-filled atmosphere, sodium pieces were mixed with graphite powder at a mass ratio of 20mg:200mg, and heat-treated at 600°C for 5 hours. After natural cooling, the low-electron-defect graphite material was obtained after water washing, filtration and drying.

[0085] The graphite material prepared in Example 3 was analyzed by electron paramagnetic resonance.

[0086] FIG. 7 is an electron paramagnetic resonance spectrum of the graphite material in Example 3 of the present disclosure.

[0087] As shown in FIG. 7, the g-factor of the graphite material prepared in Example 3 was 2.006, and the calculated electron defect concentration value was 1.05 x 1019cm-3. -5 .

[0088] Comparative Example 1

[0089] A commercial graphite material sample was analyzed using electron paramagnetic resonance.

[0090] FIG. 8 is an electron paramagnetic resonance spectrum of the commercial graphite of Comparative Example 1 of the present disclosure.

[0091] As shown in FIG. 8, the g-factor of the commercial graphite material in Comparative Example 1 was 2.002, and the calculated electron defect concentration value was 3.04 x 1019cm-3. -2 .

[0092] The commercial graphite material in Comparative Example 1 was assembled into a half-cell and tested.

[0093] FIG. 9 is a charge-discharge cycle test graph of the graphite half-cell in Comparative Example 1 of the present disclosure in an EC-based electrolyte solvent.

[0094] In the first test, the electrolyte composition was ethylene carbonate (EC), lithium hexafluorophosphate, and diethyl carbonate (DEC) (1M LiPF6+ EC:DEC = 1:1 (by volume)), and the reversible capacity was 359.9 mAhg -1 As shown in FIG. 9, the capacity retention rate was 70% after 300 cycles at a current density of 0.5C.

[0095] FIG. 10 is a charge-discharge curve of the graphite full cell in Comparative Example 1 of the present disclosure in a PC-based electrolyte solvent at room temperature.

[0096] In the second test, the electrolyte composition was propylene carbonate (PC), lithium hexafluorophosphate, and diethyl carbonate (DEC) (1M LiPF6+ PC:DEC = 1:1 (by volume)), and as shown in FIG. 10, it was directly disabled after the first discharge.

[0097] FIG. 11 is a charge-discharge curve of the graphite half-cell in Comparative Example 1 of the present disclosure in an ether-based electrolyte.

[0098] As shown in FIG. 11, the conventional commercial graphite material as a half-cell negative electrode would undergo solvent intercalation during actual charge-discharge processes, and the reversible capacity was 56.3 mAhg -1 .

[0099] Comparative Example 2

[0100] Under an argon-filled atmosphere, the lithium phosphide and graphite powder were mixed uniformly at a mass ratio of 50 mg:500 mg, heat-treated at 150°C for 5 hours, and after natural cooling, the graphite material was obtained after water washing, filtration, and drying.

[0101] The graphite material prepared in Comparative Example 2 was analyzed by electron paramagnetic resonance.

[0102] FIG. 12 is an electron paramagnetic resonance spectrum of the graphite material in Comparative Example 2 of the present disclosure.

[0103] As shown in FIG. 12, the g-factor of the graphite material g prepared in Example 1 was 2.002, and the electron defect concentration value was calculated to be 2.88 x 1019cm-3. -2 .

[0104] The graphite material prepared in Comparative Example 2 was assembled into a half-cell for testing.

[0105] FIG. 13 is a charge-discharge cycle test diagram of the graphite half-cell in Comparative Example 2 of the present disclosure in an EC-based electrolyte solvent.

[0106] In the first test, the electrolyte composition was vinyl carbonate (EC), lithium hexafluorophosphate, and diethyl carbonate (DEC) (1M LiPF6+ EC:DEC = 1:1 (volume ratio)). The reversible capacity was 359.9 mAhg-1. -1 As shown in FIG. 13, the capacity retention rate was 76% after 300 cycles at a current density of 0.5C.

[0107] In the second test, the electrolyte composition was propylene carbonate (PC), lithium hexafluorophosphate, and diethyl carbonate (DEC) (1M LiPF6+ PC:DEC = 1:1 (volume ratio)), which directly failed after the first discharge.

[0108] The electrochemical test results of Examples 1-2 and Comparative Examples 1-2 above are recorded in Tables 1 and 2 below.

[0109] Table 1

[0110] Table 2

[0111] As shown in Table 1, the low-electron-defect graphite material proposed in the present disclosure can achieve more stable cycle stability in EC-based electrolyte solvent when used as a lithium ion battery negative electrode, compared with the commercialized graphite negative electrode material in the related art, with a capacity retention rate of 85% or more after 300 cycles at a current of 0.5C; and can achieve better low-temperature performance in PC-based electrolyte solvent than in EC-based electrolyte solvent, with a room temperature capacity of 62% or more maintained at -40℃, and no lithium precipitation in long cycle. As shown in Table 2, the low-electron-defect graphite material can achieve better high-voltage resistance in PC-based electrolyte solvent than in EC-based electrolyte solvent, with stable cycle for more than 200 cycles in a charge-discharge voltage interval of 2.8-4.4V using PC-based electrolyte.

[0112] In summary, the low-electron-defect graphite material prepared in the embodiments of the present disclosure maintains good cycle stability when used as a lithium ion battery negative electrode, whether in PC-based electrolyte solvent or in EC-based electrolyte solvent. Further, the lithium ion battery in the embodiments of the present disclosure has good resistance in PC-based electrolyte solvent without other solvent addition, and can also maintain a high capacity retention rate at low temperature; while the commercialized lithium ion battery in the related art fails in PC-based electrolyte solvent. This result verifies that the low-electron-defect graphite negative electrode material can achieve stable cycle in low-temperature electrolyte, compared with the commercialized graphite negative electrode material in the related art. The applicant analyzes the reason as follows: when conventional graphite material is used as a negative electrode, solvent intercalation phenomenon inevitably occurs during charge and discharge, resulting in failure of the graphite negative electrode.

[0113] The above-described specific embodiments further illustrate the purpose, technical solutions and beneficial effects of the present disclosure, and it should be understood that the above-described specific embodiments are merely specific embodiments of the present disclosure and are not intended to limit the present disclosure. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present disclosure shall be included in the protection scope of the present disclosure.

Claims

1. A graphite material applied to a lithium battery field, wherein, The single electron defect concentration of the graphite material is less than 10 -3 spins / C atom.

2. The graphite material of claim 1, wherein, The g-factor of the graphite material is in the range of 2.004-2.008 measured by electron paramagnetic resonance spectrum.

3. A method of producing a low electron defect graphite material, comprising: The graphite is mixed with an alkali metal converting agent under a protective atmosphere and heated, and after water washing, a graphite material with low electron defects is obtained. The alkali metal converting agent includes any one of alkali metal element, alkali metal nitride and alkali metal sulfide; the single electron defect concentration of the low electron defect graphite material is less than 10 -3 spins / C atom.

4. The production method according to claim 3, wherein The heating temperature is 200-800 DEG C, and the heating time is 0.2h-30h.

5. The production method according to claim 3, wherein, The mass fraction of the alkali metal converting agent is 0.1-10wt% of the total mass of the graphite and the alkali metal converting agent.

6. The preparation method of claim 3, wherein, The alkali metal element includes at least one of lithium, sodium and potassium. The alkali metal nitrogen compound includes at least one of lithium phosphide, sodium phosphide, potassium phosphide, lithium nitride, sodium nitride, potassium nitride, lithium arsenide, sodium arsenide and potassium arsenide. The alkali metal sulfide includes at least one of lithium sulfide, sodium sulfide and potassium sulfide.

7. A lithium-ion battery, wherein, The lithium ion battery includes: a positive electrode; A negative electrode, a negative electrode material of the negative electrode being a graphite material, a single electron defect concentration of the graphite material being less than 10 -3 spins / C atom; an electrolyte, the electrolyte including a lithium salt solution, wherein the concentration of the lithium salt solution is 0.8-1.2mol / L, the solvent of the lithium salt solution includes a first solvent and a second solvent, the volume fraction of the first solvent is 30-100%, and the volume fraction of the second solvent is 0-70%; the first solvent includes at least one of propylene carbonate, 1,2-dimethoxyethane and 1,3-dioxolane, and the second solvent includes at least one of ethylene carbonate, diethyl carbonate, dimethyl carbonate and methyl ethyl carbonate; and a separator.

8. The lithium ion battery of claim 7, wherein, The lithium salt includes at least one of lithium hexafluorophosphate, lithium bisfluorosulfonimide, lithium difluoro(oxalato)borate, lithium tetrafluoroborate and lithium perchlorate. The electrolyte further includes an additive with a mass fraction of 0.1wt%-10wt%, and the additive includes at least one of fluoroethylene carbonate, difluoroethylene carbonate, vinylene carbonate and phosphite.

9. The lithium-ion battery of claim 7, wherein, The temperature range of the low-temperature environment is -40 DEG C to 0 DEG C.

10. Use of a lithium-ion battery according to any one of claims 7 to 9 in a low temperature environment, wherein ​

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