CN114709415A - Graphite material, secondary battery, and electronic device - Google Patents

Graphite material, secondary battery, and electronic device Download PDF

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Publication number
CN114709415A
CN114709415A CN202210375159.6A CN202210375159A CN114709415A CN 114709415 A CN114709415 A CN 114709415A CN 202210375159 A CN202210375159 A CN 202210375159A CN 114709415 A CN114709415 A CN 114709415A
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graphite material
negative electrode
secondary battery
pole piece
battery
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糜裕宏
何丽红
董佳丽
谢远森
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Ningde Amperex Technology Ltd
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Ningde Amperex Technology Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

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  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Materials Engineering (AREA)
  • Manufacturing & Machinery (AREA)
  • Inorganic Chemistry (AREA)
  • Battery Electrode And Active Subsutance (AREA)

Abstract

Provided are a graphite material, a secondary battery, and an electronic device, the graphite material having a crystallinity K of 2.5 to 7.0; wherein K is A002/A111And K is the ratio of the peak area of the graphite material (002) to the peak area of silicon (111) obtained by testing the graphite material added with 25 wt% of the standard sample of silicon powder by an X-ray diffraction method, and the degree of arrangement I of the graphite material is 2.0 to 4.0; the tap density of the graphite material is TD g/cm3TD is more than or equal to 0.86, and the following relation is satisfied: k is more than or equal to 3 × TD and less than or equal to 6 × TD + 1.0. The secondary battery comprises a negative pole piece; the negative pole piece comprises the graphite material, and is stable in structure and less in side reaction. When the negative pole piece is applied to a secondary battery, the thickness growth rate of the battery is small, and the capacity retention rate and the cycle performance are high.

Description

Graphite material, secondary battery, and electronic device
Technical Field
The present application relates to a graphite material, and a secondary battery and an electronic device using the same, which belong to the technical field of secondary batteries.
Background
The appearance of large screen smart phones has changed people's lifestyle in recent years. Nowadays, the dependence on the mobile phone is not only communication, but also shopping by adopting the mobile phone, and game, social and entertainment scenes are added. This requires that the expansion of the thickness of the battery for the mobile phone during shipment and use is not excessive. The expansion of the negative pole piece is reduced, the thickness of the battery can be reduced, and the method is one of important methods for improving the volume energy density of the battery.
The continuous development of the mobile internet puts higher demands on the secondary battery as a power source, further demands on the cruising ability of the mobile phone battery are put forward, and the development of the secondary battery with higher volume energy density is urgent.
Disclosure of Invention
In order to overcome the above-mentioned drawbacks, the present application provides a graphite material having a high energy density and a low expansion ratio.
One aspect of the present application provides a graphite material having a crystallinity K of 2.5 to 7.0; wherein K is A002/A111And K is the ratio of the peak area of the (002) face of the graphite material to the peak area of the (111) face of the silicon by testing the graphite material added with 25 wt% of the standard sample of silicon powder by a powder X-ray diffraction method;
the arrangement degree I of the graphite material is 2.0 to 4.0;
the tap density of the graphite material is TD g/cm3TD is more than or equal to 0.86, and the following relation is satisfied between the TD and K: k is more than or equal to 3 × TD and less than or equal to 6 × TD + 1.0.
In the above aspect, in order to achieve compatibility between processability of the graphite material, energy density, cycle expansion, and deformation of the secondary battery, the applicant has found that: the crystallinity of the graphite material is defined to be in the range of 2.5 to 7.0, the alignment degree I of the graphite material is defined to be 2.0 to 4.0, and the crystallinity K of the graphite material satisfies the formula: when K is more than or equal to 3 xTD and less than or equal to 6 xTD +1.0, the secondary battery has higher energy density, and the expansion rate of the secondary battery can be reduced as much as possible, so that the energy density and the cycle expansion of the secondary battery are controlled in a proper range. Moreover, the graphite material has excellent processability.
Among them, when the value of the crystallinity K of the graphite material is large, the energy density of the secondary battery is high, and the expansion rate (also referred to as a battery thickness growth rate) of the secondary battery increases. On the contrary, when the value of the crystallinity K of the graphite material is small, the energy density exerted in the secondary battery is low, the expansion rate of the secondary battery is low, and the deformation of the secondary battery is small. When the crystallinity is in the range of 2.5 to 7.0, it is possible to secure a high energy density of the secondary battery and also to minimize the expansion rate of the secondary battery.
Wherein I ═ IC/ISiFor the alignment degree, the peak intensity of the (002) plane of the graphite material and the peak intensity of the (111) plane of the silicon material, the intensity ratio I of which is obtained by testing graphite powder (to which a 25 wt% standard sample of silicon powder, such as Shanghai medicinal silicon metal powder of 200 mesh, is added) by powder X-ray diffraction (XRD)(002)/I(111)Namely I. The value of the arrangement degree I of the graphite material can reflect the integral orientation degree of the graphite material particles, when the value of I is larger, the integral orientation degree of the graphite material particles is relatively higher, the arrangement inside the particles is regular, the lithium intercalation of the secondary battery (namely, the discharge process of the secondary battery) is difficult, and the cyclic expansion of the secondary battery is larger; when the value of I is smaller, the whole orientation degree of the graphite material particles is lower, the arrangement inside the particles is messy, the lithium intercalation of the secondary battery (namely, the discharge process of the secondary battery) is easier, and the cyclic expansion of the secondary battery is small; therefore, the value of I is limited to 2.0 to 4.0, within which the secondary battery has a higher energy density while having a reduced expansion rate of the secondary battery.
The graphite material contains graphite secondary particles formed by aggregating a plurality of graphite primary particles, the content of the secondary particles affects the tap density of the graphite material, and the tap density of the graphite material affects the processability of the graphite material. Also, the secondary particle content affects the overall particle distribution of the anode active material, thereby affecting the anode active material crystallinity K. In order to take account of the processability of the graphite material, the energy density, the cyclic expansion and the deformation of the secondary battery, when the crystallinity K of the graphite material satisfies the formula: when K is not less than 3 XTD and not more than 6 XTD +1.0, more excellent processability can be obtained, and the energy density and the cycle expansion of the secondary battery can be in a proper range.
In some embodiments of the present application, the sphericity of the graphite material is 0.81 to 0.93. The sphericity test was performed using a QICPIC Picture Pattern Analyzer.
The sphericity of the graphite material may represent the overall shape of the graphite material particles. When the sphericity of the graphite material is in the range of 0.81 to 0.93, the electrolyte can form a uniform and stable protective film on the surface of the graphite material particles to reduce the consumption of lithium ions, the primary efficiency is high, the cycle performance of the secondary battery is better, the by-products on the surface of the graphite material particles are less, and the expansion rate is reduced. In some embodiments of the present application, the graphitic material is at 1300cm in raman spectroscopy with a laser at 532nm-1To 1400cm-1Peak intensity of the range ID and at 1580cm-1To 1620cm-1The ratio ID/IG of the peak intensity IG of the range is 0.06 to 0.16. In some embodiments of the present application, the Raman spectrum is at 1300cm with a 532nm laser-1To 1400cm-1Peak intensity of the range ID and at 1580cm-1To 1620cm-1The peak intensity IG of the range has a ratio ID/IG of 0.06, 0.07, 0.09, 0.10, 0.12, 0.14, 0.15, 0.16, or within any two of the above ranges. The ID/IG affects the thickness of a protective film formed when the secondary battery is first charged, the consumption amount of lithium ions, and the rate of lithium ion intercalation and deintercalation, thereby affecting the first efficiency of the secondary battery and the expansion rate of the secondary battery.
In some embodiments of the present application, the graphite material has a degree of graphitization Gr of 93.5% to 96.0%. In some embodiments of the present application, the degree of graphitization Gr of the graphite material is 93.5%, 94.0%, 94.4%, 94.7%, 95.0%, 95.2%, 95.4%, 95.6%, 95.8%, 96.0%, or within a range consisting of any two of the foregoing values. The graphitization degree influences the integral order degree of the graphite material and the interlayer spacing of the graphite material, further influences the capacity and energy density of the graphite material and the thickness increase rate of the battery in the cycle process of the secondary battery, and by comprehensively considering the conditions, the graphitization degree of the graphite material is 93.5-96.0%, and better performance can be obtained.
In some embodiments of the present application, the particle size Dv50 of the graphite material is 10 μm to 20 μm. In some embodiments of the present application, the graphite material has a particle size Dv50 of 10 μm, 12 μm, 14 μm, 16 μm, 18 μm, 20 μm, or within a range consisting of any two of the above values. The Dv50 of the particles can reflect the overall particle distribution of the graphite material, and the proportion of secondary particles can also influence the Dv 50. The Dv50 of the graphite particles affects the deintercalation lithium ion rate during cycling, the energy density of the secondary battery, and the expansion rate of the secondary battery, and thus, the Dv50 of the graphite material can achieve more excellent performance in a suitable range.
In some embodiments herein, the graphite material has a specific surface area (abbreviated BET) of 1.0m2G to 2.0m2(iv) g. In some embodiments of the present application, the specific surface area BET is 1.0m2/g、1.2m2/g、1.4m2/g、1.5m2/g、1.7m2/g、1.9m2/g、2.0m2In the range of any two values listed above. The specific surface area affects the first efficiency of the secondary battery, the amount of by-products during the cycle, the cycle performance, and the kinetic performance. In summary, all the indexes need to be considered comprehensively, so that the graphite material has better comprehensive performance, namely high energy density, good cycle and small expansion rate.
The application also provides a secondary battery, it includes positive pole piece, electrolyte, barrier film and negative pole piece, the negative pole piece includes the negative pole mass flow body and sets up the negative pole rete on at least one surface of the negative pole mass flow body, the negative pole rete includes negative pole active material, negative pole active material includes as above graphite material.
In some embodiments of the secondary battery described herein, the negative electrode sheet has a compacted density of 1.45g/cm3To 1.80g/cm3The compacted density may be 1.45g/cm3、1.55g/cm3、1.65g/cm3、1.75g/cm3、1.8g/cm3Or within a range consisting of any two of the values recited above.
In some embodiments of the secondary battery described herein, the porosity of the negative electrode tab is 20% to 30%, and the porosity of the negative electrode tab may be 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, or in a range of any two of the above values.
The porosity test adopts a gas displacement method, the pore volume of the sample accounts for the percentage of the total volume, and P is (V-V0)/V is multiplied by 100 percent; where V0 denotes the true volume and V denotes the apparent volume.
The higher the porosity of the negative pole piece is, the more electrolyte can be stored by the negative pole piece, which is beneficial to the circulation of the secondary battery. However, from another point of view, too much electrolyte is stored in the pores of the negative electrode plate, and the corresponding by-products are increased, which is not favorable for circulation. The lower the porosity, the electrolyte in the secondary battery is difficult to infiltrate the negative pole piece, and the lithium ion conduction is blocked in the battery circulation process, so that the circulation performance and the dynamic performance of the battery are influenced. Therefore, a suitable range of porosity is selected. In the secondary battery of the present application, the porosity of the negative electrode membrane is 20% to 30%.
In some embodiments of the secondary battery of the present application, the negative electrode tab has an OI value of 8 to 18; the OI value is a ratio of the peak area of the face (004) and the peak area of the face (110) obtained by testing the negative electrode sheet by X-ray diffraction (XRD).
The OI value, which may represent the degree of orientation of the particles of graphite material in the negative electrode sheet at the sheet level, affects cycle performance and cycle expansion. In order to achieve both the cycle expansion ratio and the cycle performance, in the present application, the negative electrode sheet has an OI value of 8 to 18, and the OI value of the negative electrode sheet may specifically be 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18 or may be within a range of any two of the above values.
In some embodiments of the secondary battery of the present application, the bond strength between the negative electrode film layer and the negative electrode current collector is 6N/m to 15N/m, and the bond strength between the negative electrode film layer and the negative electrode current collector may specifically be 6N/m, 7N/m, 8N/m, 9N/m, 10N/m, 11N/m, 12N/m, 13N/m, 14N/m, 15N/m, or within a range consisting of any two of the above values.
The binding force between the negative electrode film layer and the negative electrode current collector is too small, and the negative electrode film layer is easy to fall off from the negative electrode current collector (stripping for short) under the stress of lithium ions in the circulation process, so that the dynamic performance and the circulation performance of the battery are influenced, and further the circulation expansion is influenced; and the binding power between the negative electrode film layer and the negative electrode current collector is too high, so that more binders need to be added, and the energy density of the battery is reduced.
In some embodiments of the secondary battery of the present application, the negative electrode sheet further comprises one or more of carbon fibers, mesocarbon microbeads, a silicon-based material, a tin-based material, lithium titanate. The negative electrode sheet may include other negative active materials in addition to graphite. The mass content of these negative active materials in the negative electrode tab is preferably 5% to 10%. The present application also provides an electronic device including the secondary battery as described above.
The present application also provides a method of preparing a graphite material, the method comprising:
(1) pulverizing a precursor of the graphite material into primary particles having a Dv50 of 7 μm to 13 μm;
(3) mixing the primary particles and asphalt according to the weight ratio of 90: 10 to 80: 20, and calcining in a protective gas atmosphere to form secondary particles;
(3) and (3) mixing the primary particles in the step (1) and the secondary particles in the step (2) according to a weight ratio of 90: 10 to 10:90, and then carrying out graphitization treatment to obtain the graphite material.
In some embodiments of the production method of the present application, in the step (1), the precursor comprises needle coke.
In some embodiments of the production method of the present application, in the step (2), the protective gas includes: at least one of nitrogen or argon.
In some embodiments of the preparation method of the present application, in the step (2), the calcination temperature is 500 to 700 ℃.
In some embodiments of the preparation method of the present application, in the step (3), the graphitization temperature is 2500 ℃ to 3500 ℃.
In some embodiments of the production method of the present application, in the step (3), the primary particles and the secondary particles are mixed in a weight ratio of 60:40 to 10: 90.
Advantageous effects obtained by the present application
Compared with the existing graphite material, the graphite material can reduce the expansion of the secondary battery in the cycle process. Meanwhile, the secondary battery adopting the negative pole piece has unobvious deformation. The thickness of the secondary battery is matched with the expansion reduction of the negative pole piece, and the energy density of the secondary battery is improved. In addition, the expansion of the negative pole piece in the circulating process is small, the negative pole piece can better maintain a relatively stable structure, the side reaction is relatively less, and the circulation performance of the secondary battery is favorably improved.
Detailed Description
The present application is further illustrated by the following examples and comparative examples, which are intended to be illustrative of the present application only and are not to be construed as limiting the application to the following examples. The technical solution of the present application can be modified or replaced with equivalents without departing from the scope of the technical solution of the present application, and the modifications and the equivalents are all covered by the scope of the present application.
In this application, K (K ═ a)C/ASi) Is the crystallinity of graphite material. The crystallinity indicates the degree of crystallinity of the graphite material, and a larger value indicates a higher degree of crystallinity of the graphite material. Specifically, for graphite materials, the K value is affected by the degree of orientation of the graphite and the size of the particles. In order to achieve the purpose of reducing the thickness growth of the battery and controlling the deformation, the crystallinity K of the cathode active material of the application needs to satisfy that K is more than or equal to 2.5 and less than or equal to 7.0.
I (I ═ I) in the present applicationC/ISi) Defined as the degree of alignment of the graphitic material, can account for the degree of orientation of the graphitic material, which is closely related to the degree of expansion of the graphitic material. In order to achieve the purpose of reducing the thickness increase of the battery and simultaneously controlling the deformation of the battery, the arrangement degree I of the graphite material needs to satisfy that I is more than or equal to 2.0 and less than or equal to 4.0. At this moment, the thickness growth rate of the negative pole piece and the deformation of the battery can be well considered.
The tap density of the graphite material is TD g/cm3，TD≥0.86g/cm3The testing instrument is an FZS4-4B tap density tester, and the specific method is as followsThe standard is GB/T5162-2006 determination of tap density of metal powder.
In the application, the OI value of the negative pole piece prepared from the graphite material is more than or equal to 8 and less than or equal to 18. The test instrument was PANALYTICAL/X' pert PRO, wherein the XRD reference standard is JIS K0131-1996 General rules of X-ray diffraction analysis.
The (002) plane spacing of the graphite material of the present application was measured for the graphite crystal by powder X-ray diffraction (XRD) with a Panalytical/X' pert PRO, wherein the XRD reference standard is JIS K0131-.
The particle size of the graphite material of the present application was measured using a laser particle size analyzer, the test instrument being MasterSizer 2000. Reference is made to the GB/T19077-2016/ISO 13320:2009 particle size distribution laser diffraction method. Dv50 indicates that 50% of the total volume has a particle diameter greater than this value and 50% of the total volume has a particle diameter less than this value, and is commonly used to indicate the median particle size of the powder.
The graphitization degree tester of the present application is PANALYTICAL/X' pert PRO, wherein the XRD reference standard is JIS K0131-. During testing, the silicon powder accounts for 25% of the total mass of the silicon powder and the graphite.
Example 1
Preparation of lithium ion battery
1. Preparation of graphite materials
(1) The needle coke raw material was pulverized by a mechanical mill to obtain primary particles having a Dv50 of 9 μm.
(2) The crushed primary particles and the asphalt are mixed in a mixer according to the ratio of 85:15 for 1 hour until the mixture is uniform. The mixed material is fed into a granulation apparatus (roller furnace) in N2And heating to 600 ℃ under the atmosphere protection, and granulating to form secondary particles.
(3) Mixing the prepared primary particles and secondary particles according to the weight ratio of 40: 60, mixing in a mixing device, uniformly mixing, putting into a graphitization furnace for graphitization at 3000 ℃, cooling, demagnetizing, and screening to obtain the graphite material.
The compaction of the negative pole piece is 1.70g/cm3The OI value was 15.
Examples 2 to 34 and comparative examples 1 to 3 can be prepared by controlling the ratio of primary particles to secondary particles, the calcination temperature, the composition of the precursor, and the particle size of the precursor in the above-described preparation process, as long as the parameters of the present examples and comparative examples can be achieved.
2. Preparation of negative pole piece
Mixing the graphite material, the styrene butadiene rubber and the sodium carboxymethylcellulose according to the weight ratio of 96: 2, adding deionized water for further mixing, and uniformly stirring to obtain the cathode slurry. Coating the negative electrode slurry on a copper foil with the thickness of 12 mu m, drying, cold pressing, cutting into pieces, and welding a tab to obtain a negative electrode plate.
3. Diaphragm
Adopting a polyethylene diaphragm with the thickness of 10 mu m, wherein one side of the diaphragm is provided with an inorganic granular layer with the thickness of 2 mu m, and the inorganic granular layer is provided with Al2O3。
4. Electrolyte solution
Mixing Ethylene Carbonate (EC), Propylene Carbonate (PC) and diethyl carbonate (DEC) (in a weight ratio of 1: 1: 1) in a dry argon atmosphere, and adding lithium hexafluorophosphate (LiPF)6) Mixing uniformly to obtain electrolyte, wherein LiPF6The mass content of (A) is 12.5%. Fluoroethylene carbonate (FEC) was added to the electrolyte in an amount of 3% by mass based on the weight of the electrolyte.
5. Preparation of positive pole piece
Mixing a positive electrode active material lithium cobaltate, a conductive agent SP and a binder polyvinylidene fluoride according to the weight ratio of 97: 1.4: 1.6, adding N-methyl pyrrolidone (NMP), and stirring the mixture under the action of a vacuum stirrer until the system becomes uniform slurry to obtain positive electrode slurry, wherein the solid content of the positive electrode slurry is 72 wt%; and coating the positive electrode slurry on the surface of the positive electrode current collector, drying, cold pressing, cutting into pieces, and welding a lug to obtain the positive electrode piece.
6. Preparation of lithium ion battery
Stacking the positive pole piece, the isolating film and the negative pole piece in sequence to enable the isolating film to be positioned between the positive pole piece and the negative pole piece to play an isolating role, and then winding to obtain a battery cell; and (3) placing the battery cell in an outer packaging foil aluminum plastic film, injecting the prepared electrolyte into the dried battery cell, and performing vacuum packaging, standing, formation, shaping, capacity test and other procedures to obtain the lithium ion battery.
Test method
1. First efficiency test
After the lithium ion battery is prepared, the lithium ion battery is charged to 4.45V by a current of 0.5C and a constant current, and then charged to 0.05C by a voltage of 4.45V and a constant voltage to obtain a first charging capacity (C)0) (ii) a Then, the mixture was allowed to stand for 5 minutes, and then discharged to 3V at a current of 0.5C to obtain the first discharge capacity (D)0) First charge-discharge efficiency (i.e. first effect) ═ D0/C0×100％。
2. Increase in thickness (%)
Taking the prepared negative pole piece, taking five points on the polymer film with the same length before winding, testing the negative pole thickness corresponding to the five points, taking the average value, and recording as L0Assembling a lithium ion battery, and standing for 30 minutes in a constant temperature box at 25 ℃ to keep the temperature of the lithium ion battery constant; charging to 4.45V at a constant current of 0.5C and charging at a constant voltage until the current is 0.05C; discharging to 3.0V at 0.5C, cycling for 200 circles, charging to 4.45V at 0.5C constant current, and charging at constant voltage until the current is 0.05C; disassembling the battery, taking out the negative pole piece, determining the point taking position of the negative pole piece in the previous step by using a polymer film after the surface of the negative pole is dried, re-testing the thickness of the negative pole piece at 5 points, taking the average value, and recording the average value as L200，
Thickness increase rate (%) of the negative electrode sheet after 200 cycles (L)200-L0)/L0×100％。
3. Rate of increase of battery thickness
Standing at 25 deg.C for 5 min, charging with 0.5C constant current to 4.45V, charging with 4.45V constant voltage to 0.05C, and standingStanding for 5 minutes. Determining three positions of the lithium ion battery, determining the thicknesses of points of the three positions, and taking an average value to be marked as MMC0. Then the lithium ion battery is discharged to 3.0V at a constant current of 0.5C and is kept still for 5 minutes. Repeating the charge-discharge cycle for 200 times, testing the thicknesses of three position points of the lithium ion battery every time, and taking an average value MMC200。
The cell thickness growth rate was calculated by the following formula:
200 cycles cell thickness growth (%) - (MMC)200-MMC0)/MMC0×100％。
4. Number of cycles at 45 deg.C
Placing the lithium ion battery in a constant temperature box at 45 ℃, and standing for 30 minutes to keep the temperature of the lithium ion battery constant; charging to 4.45V at a constant current of 0.5C and charging at a constant voltage until the current is 0.05C; discharging to 3.0V at 0.5C to obtain first charge capacity (C)0) (ii) a This step is cycled until the capacity is 80% of the first charge capacity, and the number of cycles is recorded.
The parameters of the graphite materials in the examples and comparative examples are shown in Table 1.
TABLE 1
Figure BDA0003590079700000081
Figure BDA0003590079700000091
Figure BDA0003590079700000101
The results of the electrochemical performance tests in examples 1 to 34 and comparative examples 1 to 3 are shown in table 2.
TABLE 2
Figure BDA0003590079700000102
Figure BDA0003590079700000111
Figure BDA0003590079700000121
As can be seen from tables 1 and 2, the lithium ion batteries using the graphite materials of examples 1 to 34 of the present application all had a small thickness growth rate, and the cycle number at 45 ℃ was significantly higher than that of comparative examples 1 to 3, and the battery life was significantly longer than that of comparative examples 1 to 3.
In examples 1 to 34, the crystallinity K and the arrangement I of the graphite material in the negative electrode sheet satisfy 2.5. ltoreq. K.ltoreq.7.0 and 2.0. ltoreq. I.ltoreq.4.0. The expansion of the negative pole piece is reduced in the battery circulation process, meanwhile, the risks of warping and deformation of the battery are restrained, the matching between the reduction of the thickness of the negative pole piece and the reduction of the thickness of the battery is ensured, and the aim of improving the energy density of the battery is fulfilled.
Example 35 to example 39
The lithium ion battery was prepared by the same procedure as in example 12, except that: the parameters of the negative electrode pole piece in example 12 were replaced with the parameters of the negative electrode pole piece in examples 35 to 39. The relevant parameters of the negative pole piece are shown in table 3.
TABLE 3 lithium ion battery Performance parameters when different negative electrode sheet parameters were used
Figure BDA0003590079700000131
It can be known from table 3 that the battery of the negative pole piece that adopts the graphite material preparation of this application can reduce the thickness growth rate of negative pole piece, promotes the energy density of battery. The battery adopting the graphite material of the application has the advantages that the thickness growth rate is balanced with the service life and the cycle performance of the battery.
As can be seen from the data in Table 3, the negative pole piece of the application has stable structure, less side reaction, small thickness increase rate of the battery using the negative pole piece and high cycle performance.

Claims (7)

1. A graphite material, characterized in that the graphite material has a crystallinity K of 2.5 to 7.0;
wherein K is A002/A111And K is the ratio of the peak area of the (002) face of the graphite material to the peak area of the (111) face of the silicon material obtained by testing the graphite material added with 25 wt% of silicon powder by an X-ray diffraction method;
the arrangement degree I of the graphite material is 2.0 to 4.0;
the tap density of the graphite material is TD g/cm3TD is not less than 0.86, and the following relation is satisfied: k is more than or equal to 3 × TD and less than or equal to 6 × TD + 1.0.
2. The graphite material according to claim 1, wherein the graphite material satisfies at least one of conditions (1) to (5):
(1) the sphericity of the graphite material is 0.81 to 0.93;
(2) in Raman spectroscopy, the graphite material is at 1300cm-1To 1400cm-1Peak intensity of the range ID and at 1580cm-1To 1620cm-1A ratio of peak intensity IG in the range of 0.06 to 0.16;
(3) the graphitization degree Gr of the graphite material is 93.5-96.0%;
(4) the particles of the graphite material have a particle size Dv50 of 10 to 20 μm;
(5) the specific surface area of the graphite material is 1.0m2G to 2.0m2/g。
3. A secondary battery, comprising a positive electrode plate, an electrolyte, a separator and a negative electrode plate, wherein the negative electrode plate comprises a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, the negative electrode film layer comprises a negative electrode active material, and the negative electrode active material comprises the graphite material according to any one of claims 1 to 2.
4. The secondary battery according to claim 3, wherein the negative electrode tab satisfies at least one of conditions (1) or (2):
(1) the compacted density of the negative pole piece is 1.45g/cm3To 1.80g/cm3；
(2) The porosity of the negative pole piece is 20-30%.
5. The secondary battery according to claim 4, wherein the negative electrode tab has an OI value of 8 to 18;
wherein, the OI value is the ratio of the peak areas of the face (004) and the face (110) obtained by testing the negative electrode plate by an X-ray diffraction method.
6. The secondary battery according to claim 4, wherein the adhesive strength between the negative electrode film layer and the negative electrode current collector is 6N/m to 15N/m.
7. An electronic device characterized by comprising the secondary battery according to any one of claims 3 to 6.
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