CN114759157B - Negative electrode piece, preparation method thereof and lithium secondary battery - Google Patents
Negative electrode piece, preparation method thereof and lithium secondary battery Download PDFInfo
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- CN114759157B CN114759157B CN202210469031.6A CN202210469031A CN114759157B CN 114759157 B CN114759157 B CN 114759157B CN 202210469031 A CN202210469031 A CN 202210469031A CN 114759157 B CN114759157 B CN 114759157B
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- 238000002360 preparation method Methods 0.000 title abstract description 13
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- 239000010439 graphite Substances 0.000 claims abstract description 183
- 239000011148 porous material Substances 0.000 claims abstract description 89
- 239000002245 particle Substances 0.000 claims abstract description 68
- 239000012528 membrane Substances 0.000 claims abstract description 22
- 239000007773 negative electrode material Substances 0.000 claims description 35
- 238000000034 method Methods 0.000 claims description 20
- 239000011267 electrode slurry Substances 0.000 claims description 18
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- 238000005087 graphitization Methods 0.000 claims description 10
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- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 4
- QMGYPNKICQJHLN-UHFFFAOYSA-M Carboxymethylcellulose cellulose carboxymethyl ether Chemical compound [Na+].CC([O-])=O.OCC(O)C(O)C(O)C(O)C=O QMGYPNKICQJHLN-UHFFFAOYSA-M 0.000 description 4
- 239000011230 binding agent Substances 0.000 description 4
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- 229910001128 Sn alloy Inorganic materials 0.000 description 1
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 1
- HMDDXIMCDZRSNE-UHFFFAOYSA-N [C].[Si] Chemical class [C].[Si] HMDDXIMCDZRSNE-UHFFFAOYSA-N 0.000 description 1
- OBNDGIHQAIXEAO-UHFFFAOYSA-N [O].[Si] Chemical class [O].[Si] OBNDGIHQAIXEAO-UHFFFAOYSA-N 0.000 description 1
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- GBCAVSYHPPARHX-UHFFFAOYSA-M n'-cyclohexyl-n-[2-(4-methylmorpholin-4-ium-4-yl)ethyl]methanediimine;4-methylbenzenesulfonate Chemical compound CC1=CC=C(S([O-])(=O)=O)C=C1.C1CCCCC1N=C=NCC[N+]1(C)CCOCC1 GBCAVSYHPPARHX-UHFFFAOYSA-M 0.000 description 1
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- QHGNHLZPVBIIPX-UHFFFAOYSA-N tin(ii) oxide Chemical class [Sn]=O QHGNHLZPVBIIPX-UHFFFAOYSA-N 0.000 description 1
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Classifications
-
- 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
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
-
- 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
-
- 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
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/139—Processes of manufacture
-
- 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
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/624—Electric conductive fillers
- H01M4/625—Carbon or graphite
-
- 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
Abstract
The application provides a negative electrode plate, a preparation method thereof and a lithium secondary battery. The negative electrode plate comprises a negative electrode current collector and a negative electrode membrane arranged on one surface or two surfaces of the negative electrode current collector, wherein the negative electrode membrane comprises a negative electrode active substance, the negative electrode active substance comprises porous graphite, and the porous graphite satisfies the following conditions: axDv of 0.9.ltoreq.AxDv 50 C is less than or equal to 4.3; wherein, the average pore diameter of the surface pore canal of the porous graphite is A nm; volume median particle diameter of porous graphite is Dv 50 μm; the gram capacity of the porous graphite is C mAh/g. The lithium secondary battery has high energy density, long cycle life and quick charging performance by reasonably adjusting the relation among the average pore diameter of pore channels on the surface of the porous graphite in the anode active material, the gram capacity and the average particle diameter of the porous graphite.
Description
Technical Field
The application relates to the field of lithium secondary batteries, in particular to a negative electrode plate, a preparation method thereof and a lithium secondary battery.
Background
The lithium secondary battery has the outstanding characteristics of light weight, high energy density, no pollution, no memory effect, long service life and the like, and is widely applied to portable electronic equipment and new energy automobiles. However, a longer charging time is one of the important factors limiting the rapid popularization of new energy automobiles, and in terms of technical principles, the negative electrode plate has a larger influence on the rapid charging performance of the lithium secondary battery, and if the charging and discharging current is too large, part of lithium ions can be directly reduced and separated out on the surface of the negative electrode plate instead of being embedded into the negative electrode active material, so that the rapid charging performance of the secondary battery is poor.
Disclosure of Invention
The main aim of the application is to provide a negative electrode plate, a preparation method thereof and a lithium secondary battery, so as to solve the problem of poor quick charge performance of the lithium secondary battery in the prior art.
In order to achieve the above object, according to one aspect of the present application, there is provided a negative electrode tab including a negative electrode current collector and a negative electrode membrane provided on one surface or both surfaces of the negative electrode current collector, the negative electrode membrane including a negative electrode active material including porous graphite, and the porous graphite satisfying:
0.9≤A×Dv 50 /C≤4.3；
wherein, the average pore diameter of the surface pore canal of the porous graphite is A nm;
volume median particle diameter of porous graphite is Dv 50 μm；
The gram capacity of the porous graphite is C mAh/g.
Further, the porous graphite satisfies 1.5.ltoreq.AxDv 50 C3.5, preferably 2.ltoreq.AXDv 50 /C≤3。
Further, the average pore diameter of the surface pore canal of the porous graphite is 20-200 nm, preferably 20-100 nm, and more preferably 30-80 nm; and/or the volume median particle diameter of the porous graphite is 3 to 20 μm, preferably 5 to 18 μm, more preferably 8 to 15 μm; and/or the gram capacity of the porous graphite is 340-365 mAh/g, preferably 350-360 mAh/g, more preferably 353-358 mAh/g.
Further, the specific surface area of the porous graphite is 1-10 m 2 Preferably 3 to 8m 2 Preferably 4 to 6m 2 /g。
Further, the graphitization degree of the porous graphite is 80 to 99%, preferably 90 to 99%, more preferably 95 to 99%.
Further, the mass ratio of the negative electrode active material in the negative electrode membrane is 80-98%, and preferably the negative electrode active material further comprises one or more of natural graphite, artificial graphite, soft carbon, hard carbon, carbon fiber, mesophase carbon microsphere, silicon-based material, tin-based material and lithium titanate.
Further, the compacted density P of the negative electrode filmD is 1-2 g/cm 3 Preferably 1.2 to 1.8g/cm 3 More preferably 1.4 to 1.7g/cm 3 。
According to another aspect of the present application, there is provided a lithium secondary battery including a positive electrode tab, a negative electrode tab, an electrolyte, and a separator, the negative electrode tab being any one of the above-described negative electrode tabs.
Further, the lithium secondary battery also satisfies 0.5.ltoreq.Dv 50 /[V OI ×(CB+1)]≤5；
Wherein the OI value of the negative electrode membrane is V OI ；
The capacity excess coefficient of the lithium secondary battery is CB;
preferably satisfies 1.ltoreq.Dv 50 /[V OI ×(CB+1)]4 or less, more preferably 1 or less Dv 50 /[V OI ×(CB+1)]≤2。
Further, OI value V of negative electrode film OI 1 to 20, preferably 1 to 15, more preferably 1 to 8; and/or the capacity excess factor CB of the lithium secondary battery is 1.0 to 2.0, preferably 1 to 1.5, more preferably 1.1 to 1.3.
According to still another aspect of the present application, there is provided a preparation method of any one of the above negative electrode tabs, including: preparing negative electrode slurry; coating the negative electrode slurry on one or two sides of a negative electrode current collector copper foil, and drying, cold pressing and cutting to obtain a negative electrode plate; wherein, the process for preparing the negative electrode slurry comprises: selecting porous graphite according to the following relation formula I, and mixing a negative electrode active material comprising the porous graphite, a conductive agent, an adhesive and a dispersion solvent to obtain a negative electrode slurry;
0.9≤A×Dv 50 c4.3 relation I
Wherein, the average pore diameter of the surface pore canal of the porous graphite is A nm;
volume median particle diameter of porous graphite is Dv 50 μm；
The gram capacity of the porous graphite is C mAh/g;
preferably, the porous graphite is selected according to the relationship I-1:
1.5≤A×Dv 50 c is less than or equal to 3.5 and is represented by a formula I-1,
preferably, the porous graphite is selected according to the relationship I-2:
2≤A×Dv 50 and C is less than or equal to 3 and is represented by a formula I-2.
By applying the technical scheme, the energy density, the quick charge performance and the cycle performance of the battery can be considered and improved. The inventors of the present application have found through extensive studies that the average pore diameter of the porous graphite surface channels (also referred to as average pore diameter a in the present application) and the volume median particle diameter of the porous graphite (also referred to as volume median particle diameter Dv in the present application) in the negative electrode active material 50 ) And gram capacity (also referred to as gram capacity C in this application) of the porous graphite affects the quick charge capacity and service life of the battery, and the lithium secondary battery is made to give consideration to high energy density, long cycle life and quick charge performance by controlling the relationship among the average pore diameter of the pore channels on the surface of the porous graphite, the volume median particle diameter of the porous graphite and the gram capacity in combination in the negative electrode active material.
According to the application, when the battery is designed, the provided negative electrode active material comprises porous graphite, the particle surface of the porous graphite is provided with a pore canal, lithium ions can be inserted into graphite crystals through the pore canal, the dynamic performance of the lithium secondary battery is improved, and the pore canal on the surface of the porous graphite can buffer the volume change of the porous graphite in the charge-discharge process, so that the cycle performance of the lithium secondary battery is improved. In view of this, this application makes the lithium secondary battery compromise high energy density, long cycle life and quick charge performance through rationally adjusting the relation between the three of average pore diameter of porous graphite surface pore canal in the negative electrode active material, the volume median particle diameter of porous graphite and gram capacity.
Detailed Description
It should be noted that, in the case of no conflict, the embodiments and features in the embodiments may be combined with each other. The present application will be described in detail with reference to examples.
In theory, during the battery charging process, the negative electrode sheet needs to undergo the following 3 electrochemical processes: (1) Lithium ions are separated from the positive electrode material and enter the electrolyte, and liquid phase conduction is carried out inside the negative electrode porous electrode along with the electrolyte; (2) The lithium ions exchange charges on the surface of the anode active material; (3) Solid phase conduction of lithium ions inside the anode active material particles.
The charge exchange of lithium ions on the surface of the anode active material and the solid phase conduction in the particles of the anode active material have important influence on the improvement of the quick charge performance of the battery, and the charge exchange of lithium ions on the surface of the anode active material and the solid phase conduction in the material are closely related to the particle morphology and the particle structure of the anode active material.
In an exemplary embodiment of the present application, there is provided a negative electrode tab including a negative electrode current collector and a negative electrode membrane disposed on one surface or both surfaces of the negative electrode current collector, the negative electrode membrane including a negative electrode active material including porous graphite, and satisfying:
0.9≤A×Dv 50 /C≤4.3
wherein, the average pore diameter of the surface pore canal of the porous graphite is A nm;
volume median particle diameter of porous graphite is Dv 50 μm；
The gram capacity of the porous graphite is C mAh/g.
The inventors of the present application have found through extensive studies that the average pore diameter a of the surface pores of the porous graphite in the negative electrode active material and the volume median particle diameter Dv of the porous graphite 50 And gram capacity C of the porous graphite influences the quick charge capacity and the service life of the battery, and the energy density, the quick charge performance and the cycle performance of the battery can be considered and improved by jointly controlling the average pore diameter of pore channels on the surface of the porous graphite in the anode active material, the volume median particle diameter and the gram capacity of the porous graphite.
According to the application, when the battery is designed, the provided negative electrode active material comprises porous graphite, the particle surface of the porous graphite is provided with a pore canal, lithium ions can be inserted into graphite crystals through the pore canal, the dynamic performance of the lithium secondary battery is improved, and the pore canal on the surface of the porous graphite can buffer the volume change of the porous graphite in the charge-discharge process, so that the cycle performance of the lithium secondary battery is improved. In view of this, this application makes the lithium secondary battery compromise high energy density, long cycle life and quick charge performance through rationally adjusting the relation between the three of average pore diameter of porous graphite surface pore canal, gram capacity and volume median particle diameter of porous graphite in the negative electrode active material.
The average pore diameter A of the pore channels on the surface of the porous graphite in the anode active material is too large or the volume median particle diameter Dv of the porous graphite 50 Too large or too small gram capacity C of porous graphite results in A.times.Dv 50 When the upper limit of/C exceeds 4.3, the overall performance of the battery is poor. The method is characterized in that the average pore diameter A of pore channels on the surface of porous graphite in the anode active material is too large, the specific surface area of the material is too high, and active sites on the surface of the material are too many, so that side reactions between the anode active material and electrolyte are increased, and the impedance and the capacity loss of the battery are improved, so that the quick charge performance and the cycle performance of the battery are reduced; volume median particle diameter Dv of porous graphite in negative electrode active material 50 The solid-phase diffusion path of lithium ions in porous graphite particles is too long, the dynamic performance of the battery is poor, and the rapid charge and discharge are not facilitated; when the gram-volume C of the porous graphite in the negative electrode active material is too small, the energy density of the battery is too low, and the battery performance is poor.
The average pore diameter A of the pore channels on the surface of the porous graphite in the anode active material is too small or the volume median particle diameter Dv of the porous graphite 50 Too small or too large gram capacities C of porous graphite lead to A.times.Dv 50 When the lower limit of/C is less than 0.9, the overall performance of the battery is poor. The average pore diameter A of pore channels on the surface of the porous graphite in the anode active material is too small, so that the charge exchange of lithium ions on the surface of the porous graphite and the solid phase conduction capacity of the lithium ions in the porous graphite particles are poor, the dynamic performance of the battery is poor, and the rapid charge and discharge are not facilitated; volume median particle diameter Dv of porous graphite in negative electrode active material 50 Too small, the structure of the negative electrode membrane is too compact, which is not beneficial to electrolyte permeation, the liquid phase diffusion capability of lithium ions is reduced, the dynamic performance of the battery is poor, and rapid charge and discharge cannot be carried out; the excessive gram capacity C of the porous graphite in the anode active material shows that the side reaction between the porous graphite and the electrolyte is less, the specific surface area of the material is smaller, and the active site on the surface of the materialThe number of points is small, the charge exchange of lithium ions on the surface of the material is not facilitated, the dynamic performance of the battery is poor, and the battery cannot bear the faster charge and discharge speed.
On the basis, the average pore diameter A of pore channels on the surface of the porous graphite, the volume median particle diameter Dv50 of the porous graphite and the gram capacity C form a mutually restricted relation. Wherein, the average pore diameter A of pore channels on the surface of the porous graphite and the volume median particle diameter Dv of the porous graphite 50 The dynamic performance and the electrochemical cycle performance of the porous graphite are affected together, and the gram capacity C of the porous graphite can not be excessively large or small at the same time, but can directly affect the energy density of the lithium ion battery; the inventor finds that when the average pore diameter A, the volume median particle diameter Dv50 and the gram capacity C of the porous graphite are more than or equal to 0.9 and less than or equal to A multiplied by Dv50/C and less than or equal to 4.3, the battery has better comprehensive performance, proper energy density, better dynamic performance and better electrochemical cycle performance.
In order to better balance the relationship between the average pore diameter of the pore channels on the surface of the graphite, the gram capacity and the volume median particle diameter of the porous graphite, in some preferred embodiments of the present application, the porous graphite satisfies 1.5.ltoreq.A.times.Dv 50 Preferably, the porous graphite satisfies 2A multiplied by Dv, and C is not more than 3.5 50 And C is less than or equal to 3, so that the negative electrode has the characteristics of high energy density, excellent quick charge performance and long cycle life under high-rate charge and discharge.
Considering the charge exchange capacity of lithium ions on the surface of the anode active material, the larger the average pore diameter A of pore channels on the surface of the anode active material particles is, the higher the specific surface area of the material is, the more active sites on the surface of the material are, the charge exchange of lithium ions on the surface of the material is facilitated, and the rapid charging performance of a lithium ion battery can be improved; meanwhile, considering the solid-phase conduction capability of lithium ions in the cathode active material, the larger the average pore diameter A of pore channels on the surface of the cathode active material particles is, the more favorable the diffusion of lithium ions into the material is, and the solid-phase conduction capability of lithium ions in the material can be improved, so that the quick charging performance of a lithium ion battery is improved, but the larger the pore diameter of the surface of the cathode active material particles is, the more the gaps in the particles are, the lower the compaction density of a cathode membrane is, and the lower the energy density of the battery is; in addition, the method comprises the following steps. As the average pore diameter a of the pore channels on the surface of the anode active material particles increases, the battery resistance increases and causes a certain capacity loss, thereby reducing the energy density of the battery. In some embodiments of the present application, the average pore diameter of the surface pore canal of the porous graphite is 20 to 200nm, preferably 20 to 100nm, and more preferably 30 to 80nm, for example, the average pore diameter of the surface pore canal of the porous graphite is 40nm, or 50nm, or 60nm, or 70nm, so that when the pore diameter of the surface pore canal of the anode active material particle is too large, the specific surface area of the material is too high, and the active sites on the surface of the material are too many, which results in too many side reactions between the material and the electrolyte, resulting in increased battery impedance, rather decreased rapid charging performance of the battery, and also results in irreversible capacity loss, affecting the service life of the battery, and having higher conductivity and energy density of lithium ions.
Volume median particle diameter Dv of porous graphite 50 Can influence the liquid phase diffusion of lithium ions in the cathode and Dv 50 The larger is more favorable for liquid-phase diffusion of lithium ions inside the anode, but increases the solid-phase diffusion path of lithium ions inside the porous graphite particles. Volume median particle diameter Dv of porous graphite in negative electrode active material 50 Too small, the binding force of the negative electrode plate is small, powder is easy to fall off, the electronic conductivity of the negative electrode plate is influenced, and the dynamic performance of the battery is poor; volume median particle diameter Dv of porous graphite in negative electrode active material 50 The cathode slurry is easy to subside when being oversized, the appearance of the pole piece is rough during coating, the product quality rate of the cathode pole piece is low, and meanwhile, dv is low 50 The solid phase conduction capacity of lithium ions in graphite particles can be reduced excessively, and the rapid charge and discharge of the battery are not facilitated. Thus, a suitable Dv 50 Can effectively ensure the comprehensive performance of the battery, and in some embodiments of the application, the volume median particle diameter Dv of the porous graphite 50 The range of 3 to 20. Mu.m, preferably 5 to 18. Mu.m, more preferably 8 to 15. Mu.m, gives lithium batteries having more overall performance.
The larger gram capacity C of the porous graphite is the higher the battery energy density of the porous graphite, and the smaller the specific surface area is, the fewer active sites on the surface of the material are, so that the less capacity loss caused by side reaction between the porous graphite and electrolyte is caused, but the charge exchange of lithium ions on the surface of the material is not facilitated, and the quick charge performance of the battery is deteriorated. In some embodiments of the present application, the gram capacity of the porous graphite is 340-365 mAh/g, preferably 350-360 mAh/g, and more preferably 353-358 mAh/g, so that the energy density and the fast charge performance of the battery are both considered when the porous graphite is selected.
The foregoing has mentioned the average pore diameter A of the surface channels of the porous graphite, the volume median particle diameter Dv of the porous graphite 50 And the gram capacity C of the porous graphite is related to the specific surface area of the porous graphite, and besides, the morphology of the porous graphite particles and the defects on the surfaces of the particles also influence the specific surface area of the porous graphite; the larger the specific surface area of the porous graphite is, the more favorable the charge exchange of lithium ions is, and the larger the capacity loss caused by side reaction between the porous graphite and the electrolyte is. In some embodiments of the present application, the porous graphite has a specific surface area of 1 to 10m 2 Preferably 3 to 8m 2 Preferably 4 to 6m 2 /g, e.g. 4.5m 2 /g、5m 2 /g、5.5m 2 And/g, has better comprehensive performance.
Through graphitization, carbon atoms realize the transformation from a disordered layer structure to an ordered structure, so the graphitization degree of the porous graphite has great influence on the comprehensive performance of the lithium secondary battery, the higher the graphitization degree is, the higher the crystallinity of the porous graphite is, the more active sites in particles are available for lithium ion deintercalation, and the higher the capacity of the porous graphite is. In some embodiments of the present application, the degree of graphitization of the porous graphite is 80 to 99%, preferably 90 to 99%, more preferably 95 to 99%, such as 96%, 97%, 98%.
In some embodiments, the mass ratio of the negative electrode active material in the negative electrode membrane is 80-98%. In some embodiments, the negative active material may include one or more of natural graphite, artificial graphite, soft carbon, hard carbon, carbon fiber, mesophase carbon microsphere, silicon-based material, tin-based material, and lithium titanate, in addition to porous graphite, the content of which may be referred to the prior art, and in some embodiments, the mass ratio of porous graphite to the negative membrane is 10-60%. Among them, preferably, the silicon-based material may be selected from elemental silicon, silicon oxygen compounds, silicon carbon compounds, and silicon alloys, and the tin-based material may be selected from elemental tin, tin oxygen compounds, and tin alloys. When one or a combination of the above materials is applied to the anode active material, the specific amount thereof may be referred to the prior art, and the description thereof is omitted herein.
The material composition of the negative electrode membrane of the present application may be selected from the prior art, for example, a conductive agent and a binder may be included in addition to the negative electrode active material, and the types and contents of the conductive agent and the binder are not particularly limited and may be selected according to actual needs. In some embodiments of the present application, the negative electrode film has a compacted density PD of 1-2 g/cm 3 Preferably 1.2 to 1.8g/cm 3 More preferably 1.4 to 1.7g/cm 3 The battery cathode has better comprehensive performance and ensures enough energy density.
In the negative electrode sheet of the present application, the type of the negative electrode current collector is not particularly limited, and may be selected according to actual requirements in the prior art, for example, copper foil is selected.
In another embodiment of the present application, a lithium secondary battery is provided, which includes a positive electrode tab, a negative electrode tab, an electrolyte, and a separator, wherein the negative electrode tab is any one of the negative electrode tabs described above.
When the lithium secondary battery is designed, the adopted negative electrode active material comprises porous graphite, the particle surface of the porous graphite is provided with pore channels, lithium ions can be inserted into graphite crystals through the pore channels, the dynamic performance of the lithium secondary battery is improved, and the pore channels on the surface of the porous graphite can buffer the volume change of the porous graphite in the charge and discharge process, so that the cycle performance of the lithium secondary battery is improved. In view of this, this application makes the lithium secondary battery compromise high energy density, long cycle life and quick charge performance through rationally adjusting the relation between the three of average pore diameter of porous graphite surface pore canal, gram capacity and volume median particle diameter of porous graphite in the negative electrode active material.
The types and compositions of the positive electrode sheet, the electrolyte and the isolating film of the lithium secondary battery can be selected according to actual requirements in the prior art, and the application is not limited.
In some embodiments of the present application, the lithium secondary battery also satisfies 0.5 +.dv 50 /[V OI ×(CB+1)]≤5；
Wherein the OI value of the negative electrode membrane is V OI ；
The capacity excess coefficient of the lithium secondary battery is CB.
Volume median particle diameter Dv of porous graphite in negative electrode active material 50 OI value V of too small or negative electrode film OI Too large or too large a battery capacity excess factor CB leads to Dv 50 /[V OI ×(CB+1)]Below 0.5, the improvement of the comprehensive performance of the battery is not obvious; volume median particle diameter Dv of porous graphite in negative electrode active material 50 OI value V of oversized or negative diaphragm OI Too small or too small a battery capacity excess factor CB leads to Dv 50 /[V OI ×(CB+1)]When the upper limit of (2) exceeds 5, the improvement in the overall performance of the battery is not significant. In some preferred embodiments of the present application, the lithium secondary battery satisfies 1.ltoreq.Dv 50 /[V OI ×(CB+1)]4 or less, more preferably 1 or less Dv 50 /[V OI ×(CB+1)]≤2。
Wherein the OI value V of the negative electrode membrane OI Neither too large nor too small, due to the OI value V of the negative electrode film OI Too small, the negative electrode active substances tend to be arranged in disorder, the effective end faces of the negative electrode plates for lithium ion deintercalation are more, but the cohesive force of the negative electrode plates is poor, powder is easy to fall off, the structural stability of the negative electrode plates in the circulation process is poor, and the battery capacity circulation is easy to jump; OI value V of negative electrode film OI The active material of the negative electrode tends to be arranged in parallel with the current collector of the negative electrode, the effective end face of the negative electrode plate, which can be used for lithium ion deintercalation, is less, the dynamic performance of the battery is affected, and the charge and discharge efficiency is affected. In some embodiments of the present application, the negative electrode membrane has an OI value V OI From 1 to 20, preferably from 1 to 15, more preferably from 1 to 8.
The capacity excess coefficient CB of the battery is the ratio of the negative electrode capacity to the positive electrode capacity under the same area, and the size of the battery can be tested according to the prior art method, for example, the positive electrode capacity and the negative electrode capacity can be obtained by respectively assembling a positive electrode plate and a negative electrode plate with the same area and a lithium plate into a button battery and then testing the charging capacity by using a blue electric tester. In some embodiments of the present application, the capacity excess factor CB of the lithium secondary battery is 1.0 to 2.0, preferably 1 to 1.5, and more preferably 1.1 to 1.3.
The capacity excess factor CB of the lithium secondary battery is in a suitable range to significantly improve the performance of the lithium secondary battery. The capacity excess coefficient CB of the battery is too small, the negative electrode is in an excessively high SOC state in a full charge state of the battery, the potential of the negative electrode is too low easily caused by polarization in the process of high-rate charge and discharge of the battery, active lithium is easily reduced and separated out on the surface of the negative electrode, the cycle performance of the battery is reduced, and potential safety hazards are possibly caused; the capacity excess coefficient CB of the battery is overlarge, the content of the negative electrode active material is more, the negative electrode plate is thicker, the liquid phase diffusion capability of lithium ions in the negative electrode membrane is poorer, the battery is not beneficial to rapid charge and discharge, the utilization rate of the negative electrode active material is lower during full charge, and the energy density of the battery is also reduced.
In yet another embodiment of the present application, there is provided a method for preparing any one of the foregoing negative electrode sheets, the method comprising: preparing negative electrode slurry; coating the negative electrode slurry on one or two sides of a negative electrode current collector copper foil, and drying, cold pressing and cutting to obtain a negative electrode plate; wherein, the process for preparing the negative electrode slurry comprises: selecting porous graphite according to the following relation formula I, mixing a negative electrode active material comprising the porous graphite with a conductive agent, a binder and a dispersion solvent to obtain a negative electrode slurry;
0.9≤A×Dv 50 c4.3 relation I
Wherein, the average pore diameter of the surface pore canal of the porous graphite is A nm;
volume median particle diameter of porous graphite is Dv 50 μm；
The gram capacity of the porous graphite is C mAh/g;
preferably, the porous graphite is selected according to the relationship I-1:
1.5≤A×Dv 50 /C≤3.5 relation I-1
Preferably, the porous graphite is selected according to the relationship I-2:
2≤A×Dv 50 c is less than or equal to 3 and is represented by the formula I-2
When the lithium secondary battery is prepared by adopting the method, the adopted negative electrode active material comprises porous graphite, the particle surface of the porous graphite is provided with pore channels, lithium ions can be inserted into graphite crystals through the pore channels, the dynamic performance of the lithium secondary battery is improved, and the pore channels on the surface of the porous graphite can also buffer the volume change of the porous graphite in the charge and discharge process, so that the cycle performance of the lithium secondary battery is improved. In view of this, the present application selects porous graphite in the anode active material by the above-mentioned relational expression, and makes use of the relationship among the average pore diameter of the surface pore canal, the gram capacity of the porous graphite, and the volume median particle diameter, so that the lithium secondary battery gives consideration to high energy density, long cycle life, and rapid charging performance.
The specific preparation method of the anode slurry may be selected from the prior art, and the application is not limited, and in some embodiments of the application, the anode slurry is prepared by the following method: adding deionized water, conductive carbon black and 70% CMC powder into a stirring tank, and stirring at a low speed for 2 hours to form conductive glue solution; adding porous graphite into the conductive glue solution, stirring for 1h at a low viscosity and a high speed to form a first mixed solution; adding xanthan gum into the first mixed solution, stirring at high viscosity and high speed for 1h to form a second mixed solution; and adding ethanol and the rest 30% of CMC powder into the second mixed solution, and stirring at a low viscosity and a high speed for 2 hours to obtain the cathode slurry.
The advantages that can be achieved by the present application will be further described below in connection with examples and comparative examples.
The lithium secondary batteries of examples and comparative examples were each prepared in the following manner.
(1) Preparation of positive electrode plate
Mixing an anode active material NCM811, a conductive agent carbon nano tube and a binder PVDF according to a mass ratio of 94:3:4, adding a solvent NMP, and uniformly stirring the mixture to obtain anode slurry; and uniformly coating the positive electrode slurry on two sides of a positive electrode current collector aluminum foil, drying in an oven, and then carrying out cold pressing and slitting to obtain a positive electrode plate.
(2) Preparation of negative electrode plate
Firstly, preparing negative electrode slurry, wherein the proportion of negative electrode active substances, conductive carbon black, CMC and xanthan gum in the negative electrode slurry is 93:1.5:1.5:4, the solid content is 50%, and the specific preparation method of the negative electrode slurry comprises the following steps: adding deionized water, conductive carbon black and 70% CMC powder into a stirring tank, and stirring at a low speed for 2 hours to form conductive glue solution; adding a negative electrode active material into the conductive glue solution, and stirring at a low viscosity and a high speed for 1h to form a first mixed solution; adding xanthan gum into the first mixed solution, stirring at high viscosity and high speed for 1h to form a second mixed solution; and adding ethanol and the rest 30% CMC powder into the second mixed solution, stirring at a low viscosity and a high speed for 2 hours to obtain negative electrode slurry, wherein the ratio of deionized water to ethanol in the slurry is 9:1. Wherein the anode active material is selected from porous graphite or a mixture of porous graphite and other active materials at different mass ratios according to the principle in table 1, and specific compositions of the anode active materials in each example and comparative example are shown in table 1, wherein the artificial graphite is selected from the group consisting of fir SS1-P15; and uniformly coating the negative electrode slurry on two sides of a negative electrode current collector copper foil, drying in an oven, and then cold pressing and slitting to obtain a negative electrode plate.
(3) Preparation of electrolyte
Mixing Ethylene Carbonate (EC), ethylmethyl carbonate (EMC) and diethyl carbonate (DEC) according to a volume ratio of 1:1:1 to obtain an organic solvent, and then mixing the fully dried lithium salt LiPF according to a concentration of 1mol/L 6 Dissolving in the mixed organic solvent, and fully dissolving to obtain the electrolyte.
(4) Preparation of a separator film
Polyethylene film was selected as the separator film.
(5) Preparation of lithium secondary battery
Sequentially stacking the positive pole piece, the isolating film and the negative pole piece, enabling the isolating film to be positioned between the positive pole piece and the negative pole piece to play a role of isolation, and then winding to obtain a bare cell; and placing the bare cell in an outer packaging shell, drying, injecting electrolyte, and performing vacuum packaging, standing, formation, shaping and other procedures to obtain the lithium secondary battery.
Next, performance test methods of lithium secondary batteries in examples and comparative examples are described.
(1) Kinetic performance test: and (3) fully charging the lithium secondary batteries prepared in the examples and the comparative examples at the temperature of 25 ℃ for 10 times at the 4C multiplying power, fully discharging at the 1C multiplying power, fully charging the lithium ion battery at the 4C multiplying power, then disassembling the negative electrode plate, and observing the lithium precipitation condition on the surface of the negative electrode plate. The area of the lithium-separating area on the surface of the negative electrode plate is less than 5 percent and is regarded as slight lithium separation, the area of the lithium-separating area on the surface of the negative electrode plate is 5 to 40 percent and is regarded as moderate lithium separation, and the area of the lithium-separating area on the surface of the negative electrode plate is greater than 40 percent and is regarded as serious lithium separation.
(2) And (3) testing the cycle performance: the lithium secondary batteries prepared in examples and comparative examples were charged at 2C rate and discharged at 1C rate at 25C, and full charge discharge cycle test was performed until the capacity of the lithium secondary batteries was attenuated to 80% of the initial capacity, and the number of cycles was recorded.
(3) Actual energy density test: at 25 ℃, fully charging the lithium ion batteries prepared in the examples and the comparative examples at 1C multiplying power, fully discharging at 1C multiplying power, and recording the actual discharge energy at the moment; weighing the lithium ion battery at 25 ℃ by using an electronic balance; the ratio of the actual discharge energy of the lithium ion battery 1C to the weight of the lithium ion battery is the actual energy density of the lithium ion battery. Wherein when the actual energy density is less than 80% of the target energy density, the actual energy density of the battery is considered to be very low; when the actual energy density is greater than or equal to 80% of the target energy density and less than 95% of the target energy density, the actual energy density of the battery is considered to be lower; when the actual energy density is more than or equal to 95% of the target energy density and less than 105% of the target energy density, the actual energy density of the battery is considered to be moderate; when the actual energy density is more than or equal to 105% of the target energy density and less than 120% of the target energy density, the actual energy density of the battery is considered to be higher; when the actual energy density is 120% or more of the target energy density, the actual energy density of the battery is considered to be very high.
(4) Average pore diameter a of porous graphite surface pore channel test: the adsorption quantity and adsorption desorption isotherms of each partial pressure point are measured by using a nitrogen adsorption microporous aperture analyzer (3H-2000 PM 1) and by feeding and extracting air into a sample tube in a liquid nitrogen environment. And then the aperture parameter is calculated by BJH theory.
(5) Volume median particle diameter Dv of porous graphite 50 : the sample particles are dispersed in a liquid medium at a concentration of 200 to 300mg/L by using a laser diffraction particle size analyzer (MS 2000), and a single-color beam (typically a laser) is passed therethrough. After light is scattered by the particles, the light is distributed over different angles, and the values received by the regular multisensor over a number of angles are recorded for analysis. And calculating a scattering value by using a Rayleigh scattering formula to obtain the ratio of the particle volume of each particle size level to the total volume, thereby obtaining the volume distribution of the particle size.
(6) Gram capacity C of porous graphite: after a negative electrode plate is prepared by taking porous graphite as a negative electrode active substance, the negative electrode plate and a lithium sheet are assembled together to form a button cell, and then a blue electric tester (CT 2001A) is used for testing the charging capacity to obtain the battery.
(7) OI value V of negative electrode film OI : obtained by using an X-ray powder diffractometer (X' pert PRO), an X-ray diffraction pattern is obtained according to the rule of X-ray diffraction analysis and the lattice parameter measurement method of graphite JIS K0131-1996, JB/T4220-2011, and according to the formula V OI The OI value of the negative electrode membrane is calculated as C004/C110, wherein C004 is the peak area of the 004 characteristic diffraction peak and C110 is the peak area of the 110 characteristic diffraction peak.
(8) Capacity excess coefficient CB of battery: the positive electrode capacity and the negative electrode capacity can be obtained by respectively assembling a positive electrode plate and a negative electrode plate with the same area with a lithium plate to form a button cell and then testing the charging capacity by using a blue electric tester (CT 2001A).
(9) Specific surface area of porous graphite: the specific surface area of the sample is calculated by using a BET adsorption isotherm equation after the adsorption amount of the sample to be detected is determined according to the pressure or weight change before and after adsorption.
(10) Degree of graphitization of porous graphite: porous graphite powder was mixed with standard silica fume in a 1:2 ratio and tested using a bench X-ray diffractometer (aeros). And testing C002 and Si 111 crystal planes or C004 and Si 311 crystal planes by an internal standard method to obtain corrected angle data of the C002 or Si 111 crystal planes, obtaining a crystal plane distance d by using a Bragg equation, and calculating graphitization degree by using a franklin equation.
(11) Compaction density PD of negative electrode membrane: and weighing the negative electrode plate with the area A, recording the mass M of the negative electrode plate, weighing the negative electrode current collector with the same area, and recording the mass M of the negative electrode current collector. The thickness of the negative electrode sheet is measured as D, the thickness of the negative electrode current collector is measured as D, and the compaction density of the negative electrode membrane is calculated according to PD= (M-M)/[ A× (D-D) ].
Tables 1 and 2 below show the parameters and test results of examples 1 to 37 and comparative examples 1 to 3 of the present application.
TABLE 1
TABLE 2
As can be seen from examples and comparative examples, when the average pore diameter A of the porous graphite, the volume median particle diameter Dv of the porous graphite 50 Gram capacity C of porous graphite satisfies A x Dv 50 And when the ratio is within the value range, the energy density of the lithium battery is proper, and the dynamic performance and the cycle performance are good. Whereas the porous graphite of the comparative example was AXDv 50 When the numerical value of/C is less than 0.9 or more than 4.3, the lithium is more severely separated and the cycle performance is poor, and even if the average pore diameter A of the porous graphite and the volume median particle diameter Dv of the porous graphite are 50 And the gram capacity C of the porous graphite are each in the respective suitable value ranges mentioned herein, but do not satisfy 0.9. Ltoreq.AxDv 50 When the ratio of C is less than or equal to 4.3, the performance of the battery is also not ideal.
From the above description, it can be seen that the average pore diameter A of the porous graphite surface channels in the anode material, the volume median particle diameter Dv of the porous graphite 50 And gram capacity C of the porous graphite influences the quick charge capacity and service life of the battery, and the energy density, the quick charge performance and the cycle performance of the battery can be considered and improved by jointly controlling the average pore diameter of pore channels on the surface of the porous graphite in the anode material, the volume median particle diameter and the gram capacity of the porous graphite.
According to the application, when the battery is designed, the provided negative electrode active material comprises porous graphite, the particle surface of the porous graphite is provided with a pore canal, lithium ions can be inserted into graphite crystals through the pore canal, the dynamic performance of the lithium secondary battery is improved, and the pore canal on the surface of the porous graphite can buffer the volume change of the porous graphite in the charge-discharge process, so that the cycle performance of the lithium secondary battery is improved. In view of this, this application makes the lithium secondary battery compromise high energy density, long cycle life and quick charge performance through rationally adjusting the relation between the three of average pore diameter of porous graphite surface pore canal, gram capacity and volume median particle diameter of porous graphite in the negative electrode active material.
The foregoing is merely a preferred embodiment of the present application and is not intended to limit the present application, and various modifications and variations may be made to the present application by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application should be included in the protection scope of the present application.
Claims (23)
1. The utility model provides a lithium secondary battery, includes positive pole piece, negative pole piece, electrolyte and barrier film, its characterized in that, the negative pole piece includes negative pole current collector and sets up the negative pole diaphragm on a surface or two surfaces of negative pole current collector, the negative pole diaphragm includes negative pole active material, the negative pole active material includes porous graphite, just porous graphite satisfies:
0.9≤A×Dv 50 /C≤4.3；
wherein the average pore diameter of the surface pore canal of the porous graphite is A nm, and A is 20-200;
the volume median particle diameter of the porous graphite is Dv 50 μm，Dv 50 3-20;
the gram capacity of the porous graphite is C mAh/g, and C is 340-365;
and the lithium secondary battery also satisfies Dv of 0.5-0 50 /[V OI ×(CB+1)]≤5；
Wherein the OI value of the negative electrode membrane is V OI ， V OI 1-20;
the capacity excess coefficient of the lithium secondary battery is CB, and CB is 1.0-2.0.
2. The lithium secondary battery according to claim 1, wherein the porous graphite satisfies 1.5.ltoreq.A.times.Dv 50 /C≤3.5。
3. The lithium secondary battery according to claim 1, wherein the porous graphite satisfies 2.ltoreq.a×dv 50 /C≤3。
4. The lithium secondary battery according to claim 1 or 2, characterized in that the average pore diameter of the surface pore channels of the porous graphite is 20-100 nm;
and/or the volume median particle diameter of the porous graphite is 5-18 mu m;
and/or the gram capacity of the porous graphite is 350-360 mAh/g.
5. The lithium secondary battery according to claim 1 or 2, wherein the average pore diameter of the surface pore channels of the porous graphite is 30-80 nm;
and/or the volume median particle diameter of the porous graphite is 8-15 mu m;
and/or the gram capacity of the porous graphite is 353-356 mAh/g.
6. The lithium secondary battery according to claim 1 or 2, wherein the porous graphite has a specific surface area of 1 to 10m 2 /g。
7. The lithium secondary battery according to claim 1 or 2, wherein the porous graphite has a specific surface area of 3 to 8m 2 /g。
8. The lithium secondary battery according to claim 1 or 2, wherein the porous graphite has a specific surface area of 4 to 6m 2 /g。
9. The lithium secondary battery according to claim 1 or 2, wherein the graphitization degree of the porous graphite is 80 to 99%.
10. The lithium secondary battery according to claim 1 or 2, wherein the graphitization degree of the porous graphite is 90 to 99%.
11. The lithium secondary battery according to claim 1 or 2, wherein the graphitization degree of the porous graphite is 95 to 99%.
12. The lithium secondary battery according to claim 1, wherein the mass ratio of the negative electrode active material to the negative electrode membrane is 80 to 98%.
13. The lithium secondary battery according to claim 1, wherein the negative electrode active material further comprises one or more of natural graphite, artificial graphite, soft carbon, hard carbon, carbon fiber, mesophase carbon microsphere, silicon-based material, tin-based material, and lithium titanate.
14. The lithium secondary battery according to claim 1, wherein the negative electrode film has a compacted density PD of 1 to 2g/cm 3 。
15. The lithium secondary battery according to claim 1, wherein the negative electrode film has a compacted density PD of 1.2 to 1.8g/cm 3 。
16. The lithium secondary battery according to claim 1, wherein the negative electrode film has a compacted density PD of 1.4 to 1.7g/cm 3 。
17. The lithium secondary battery according to claim 1, wherein the lithium secondary battery satisfies:
1≤Dv 50 /[V OI ×(CB+1)]≤4。
18. the lithium secondary battery according to claim 1, wherein the lithium secondary battery satisfies: dv is not less than 1 50 /[V OI ×(CB+1)]≤2。
19. The lithium secondary battery according to claim 1, wherein the negative electrode film has an OI value V OI 1-15;
and/or the capacity excess coefficient CB of the lithium secondary battery is 1-1.5.
20. The lithium secondary battery according to claim 1, wherein the negative electrode film has an OI value V OI 1-8;
and/or the capacity excess coefficient CB of the lithium secondary battery is 1.1-1.3.
21. A method of producing a lithium secondary battery according to any one of claims 1 to 20, characterized in that the method of producing comprises:
preparing negative electrode slurry;
coating the negative electrode slurry on one or two sides of a negative electrode current collector copper foil, and drying, cold pressing and cutting to obtain a negative electrode plate;
wherein, the process for preparing the negative electrode slurry comprises the following steps:
selecting porous graphite according to the following relation formula I, and mixing a negative electrode active material comprising the porous graphite, a conductive agent, an adhesive and a dispersion solvent to obtain negative electrode slurry;
0.9≤A×Dv 50 and C is less than or equal to 4.3.
22. The method for producing a lithium secondary battery according to claim 21, wherein the porous graphite is selected according to the relation I-1:
1.5≤A×Dv 50 and C is less than or equal to 3.5 and is represented by the formula I-1.
23. The method for producing a lithium secondary battery according to claim 21, wherein the porous graphite is selected according to the relation I-2:
2≤A×Dv 50 and C is less than or equal to 3 and is represented by a formula I-2.
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| CN113644241A (en) * | 2021-07-15 | 2021-11-12 | 恒大新能源技术(深圳)有限公司 | Composite graphite negative electrode material, preparation method thereof and secondary battery |
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| CN109962236A (en) * | 2018-04-28 | 2019-07-02 | 宁德时代新能源科技股份有限公司 | Secondary battery |
| CN111668452A (en) * | 2019-03-06 | 2020-09-15 | 宁德时代新能源科技股份有限公司 | Negative electrode and lithium ion secondary battery thereof |
| CN113207314A (en) * | 2019-12-03 | 2021-08-03 | 宁德时代新能源科技股份有限公司 | Secondary battery, device, artificial graphite and preparation method |
| CN113644241A (en) * | 2021-07-15 | 2021-11-12 | 恒大新能源技术(深圳)有限公司 | Composite graphite negative electrode material, preparation method thereof and secondary battery |
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