CN116190565B - Lithium ion battery - Google Patents
Lithium ion battery Download PDFInfo
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- CN116190565B CN116190565B CN202310412740.5A CN202310412740A CN116190565B CN 116190565 B CN116190565 B CN 116190565B CN 202310412740 A CN202310412740 A CN 202310412740A CN 116190565 B CN116190565 B CN 116190565B
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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
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
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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
- 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
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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
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
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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
- H01M2004/021—Physical characteristics, e.g. porosity, surface area
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- 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 lithium ion battery, which comprises an anode and a cathode, wherein the cathode comprises a cathode current collector and a cathode active material layer arranged on the surface of the cathode current collector; the positive electrode comprises a positive electrode current collector and a positive electrode active material layer arranged on the surface of the positive electrode current collector; wherein the cathode active material layer has tortuosity T 2 Tortuosity T with negative electrode active material layer 1 Is 0.7 < T 2 /T 1 < 1.8. By controlling the tortuosity ratio of the positive electrode active material layer to the negative electrode active material layer, the constructed lithium ion transmission pore canal is favorable for realizing full infiltration of electrolyte to the electrode plate and rapid transmission of lithium ions, and effectively ensures that each particle periphery in the electrode has good electrochemical environment, namely a full electron and lithium ion transmission network, so that the problems of cracking, peeling and the like of the active material layer caused by anisotropic volume change are avoided, and the rate performance and long-term cycling stability of the battery are further improved.
Description
Technical Field
The application relates to the technical field of batteries, in particular to a lithium ion battery.
Background
Under the pressure of energy crisis and environmental pollution problems, safety, environmental protection and energy conservation have become the subjects of the current automobile development, and new energy automobiles are highly valued and strongly supported by traffic and energy departments because of the energy conservation, environmental protection and pollution-free advantages; the lithium battery is used as a key of a new energy automobile, plays a very important role in the new energy automobile, and with the continuous development of the new energy field, various performance requirements on the lithium battery are also higher and higher.
However, in the current lithium ion battery charging process, the deintercalation rate of lithium ions at the positive electrode is far greater than the intercalation rate of lithium ions at the negative electrode, so that after the lithium ions are rapidly deintercalated from the positive electrode, the active material layer on the surface of the negative electrode cannot fully intercalate the lithium ions transferred from the positive electrode into the active material layer, and the redundant lithium ions can be deposited on the surface of the negative electrode to form lithium dendrites, so that irreversible chemical reaction occurs to the lithium ion battery, and the capacity of the battery is attenuated and the cycle performance is reduced; seriously, when lithium dendrites accumulate to a certain degree, the risk of shorting the anode and the cathode caused by puncturing the diaphragm exists, and fire is caused when the lithium dendrites are serious, so that great potential safety hazard is caused.
Therefore, it is needed to provide a lithium battery with good matching effect of the lithium removal effect of the positive electrode plate and the lithium insertion effect of the negative electrode plate, and the cycle performance of the lithium battery is ensured while the maximum transmission efficiency of lithium ions at the battery level is ensured.
Disclosure of Invention
In order to improve the cycle performance of a lithium battery, the application provides a lithium ion battery.
The application provides a lithium ion battery, which adopts the following technical scheme:
a lithium ion battery comprising a positive electrode and a negative electrode, wherein the negative electrode comprises a negative electrode current collector and a negative electrode active material layer arranged on the surface of the negative electrode current collector; the positive electrode comprises a positive electrode current collector and a positive electrode active material layer arranged on the surface of the positive electrode current collector; wherein the positive electrode active material layer has a tortuosity T 2 Tortuosity T with the negative electrode active material layer 1 Is 0.7 < T 2 /T 1 ＜1.8。
The application is based on that the diffusion speed of lithium ions in the positive pole piece is far faster than that in the negative pole piece, and the transmission condition of lithium ions on the positive pole piece is regulated and controlled by collocation of tortuosity of the positive and negative active material layers according to the following conditions of 0.7 < T 2 /T 1 The collocation principle less than 1.8 is selected to construct the lithium ion battery claimed by the application, so that lithium ions can be smoothly transferred between the anode and the cathode in the working process of the lithium ion battery provided by the application, on one hand, lithium precipitation caused by excessive lithium ions accumulated on the surface of the cathode is avoided, on the other hand, the structural stability of the anode and the cathode of the lithium ion battery is improved, the problem that the structure of an electrode active material is damaged due to unsmooth lithium ion transmission in long-term circulation is solved, and the circularity and the storage performance of the lithium ion battery are optimized.
Detailed Description
For a better understanding and implementation, the technical solutions of the present application will be clearly and completely described below in connection with examples.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the description of the application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.
Unless otherwise indicated, all numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term "about". Accordingly, unless indicated to the contrary, the numerical parameters set forth herein are approximations that may vary depending upon the desired properties to be obtained.
As used herein, "and/or" means one or all of the elements mentioned.
The use of "including" and "comprising" herein encompasses both the situation in which only the elements are mentioned and the situation in which other elements not mentioned are present in addition to the elements mentioned.
All percentages in the present application are by weight unless otherwise indicated.
As used in this specification, the terms "a," "an," "the," and "the" are intended to include "at least one" or "one or more," unless otherwise specified. For example, "a component" refers to one or more components, and thus more than one component may be considered and possibly employed or used in the practice of the embodiments.
The lithium ion battery comprises a positive electrode and a negative electrode, wherein the negative electrode comprises a negative electrode current collector and a negative electrode active material layer arranged on the surface of the negative electrode current collector; the positive electrode comprises a positive electrode current collector and a positive electrode active material layer arranged on the surface of the positive electrode current collector; wherein the positive electrode active material layer has a tortuosity T 2 Tortuosity T with the negative electrode active material layer 1 Is 0.7 < T 2 /T 1 ＜1.8。
By controlling the tortuosity of the positive electrode active material layer and the negative electrode active material layer, the construction of the lithium ion transmission pore canal constructed under the tortuosity is favorable for the full infiltration of the electrolyte to the pole piece and the rapid transmission of lithium ions, so that good electrochemical environment, namely a full electron and lithium ion transmission network, can be effectively ensured around each particle in the electrode, the uniformity of electrochemical reaction in the electrode is ensured, the problems of cracking of the particles, separation of the active material and a current collector and the like caused by anisotropic volume change are effectively avoided, and the multiplying power performance and long-term circulation stability of the electrode are further improved.
Preferably, the cathode active material layer has a tortuosity of 3 < T 2 ＜10。
By controlling the tortuosity of the positive electrode active material layer, lithium ions can be separated from the positive electrode at a proper speed, and the charging capacity of the positive electrode at a constant current stage in high-rate charging is improved, so that the charging constant current ratio is improved, and the cycle performance of the battery is further improved.
Preferably, the cathode active material layer has a tortuosity of 4.ltoreq.T 1 ＜9。
By controlling the tortuosity of the anode active material layer, lithium ions can be timely inserted into the anode active coating, the occurrence of lithium precipitation of the anode is reduced, the contact area of the anode and electrolyte is reduced, the occurrence of side reaction is reduced, and the cycle performance of the battery is improved.
Preferably, the cathode active material layer has a tortuosity T 2 Tortuosity T with the negative electrode active material layer 1 The ratio of (2) satisfies 0.85.ltoreq.T 2 /T 1 ≤1.65。
Preferably, the thickness of the positive electrode active material layer is 70 to 160 μm and/or the thickness of the negative electrode active material layer is 90 to 220 μm.
Preferably, the thickness of the positive electrode active material layer is 105 to 160 μm, and/or the thickness of the negative electrode active material layer is 120 to 220 μm.
The overall thickness of the positive electrode active material layer after the current collector is removed by the positive electrode plate and the overall thickness of the negative electrode active material layer after the current collector is removed by the negative electrode plate are controlled, so that the matching effect of tortuosity of the positive electrode plate active material layer is more excellent, and the lithium battery with high multiplying power and excellent cycle performance is prepared.
Preferably the positive electrode active material layer has a compact density Cd of 2.8g/cm 3 ≤Cd≤3.8g/cm 3 。
The thickness and the compaction density of the positive electrode active material layer are adjusted, the porosity in the positive electrode active material layer is controlled within a certain range while the thickness of a high pole piece is ensured, so that the tortuosity of the positive electrode active material layer is kept within the range, and the positive electrode active material layer and the negative electrode are combined to act together, and the cycle performance of the battery is improved.
Preferably, the anode active material layer of at least one surface of the anode current collector includes an underlying active material layer close to the anode current collector and a surface active material layer distant from the anode current collector; the particle size of the particles constituting the bottom active material layer satisfies D50 of 5 μm or less and 9 μm or less, and the particle size of the particles constituting the surface active material layer satisfies D50 of 10 μm or less and 15 μm or less.
The porosity distribution of the upper layer and the lower layer in the anode active material layer is regulated, on one hand, the material with larger particle size is used for forming the surface active material layer, so that the large porosity of the surface layer is ensured, a quick path is provided for ion transmission, the enrichment of lithium ions on the surface of the anode is reduced, the anode can be better matched with the anode, and the lithium battery with excellent cycle performance and storage performance is formed; on the other hand, through the design of top layer macroporosity, the little porosity of bottom, alleviate the circumstances that the porosity of top layer active material layer reduces gradually, the porosity of bottom active material layer increases gradually that leads to owing to the continuous release of top layer active material layer/bottom active material layer on the negative pole piece, thereby further promote the stability of negative pole active material layer, make the negative pole piece can cooperate with the positive pole piece, further improve the circulation stability of battery.
Preferably, a hole is provided in the anode active material layer of at least one surface of the anode current collector, in the anode active material layer, a ratio of a depth of the hole to a thickness of the anode active material layer is 0.09 to 0.96, and a pore diameter of the hole is 2 to 80 μm.
Preferably, when the shape of the hole opened in the anode active material layer is regular, the pore diameter of the hole is the true pore diameter of the hole; when the shape of the hole opened in the anode active material layer is irregular, the aperture of the hole refers to the distance from the center of the hole to any point of the edge of the hole.
Preferably, the depth of the holes is 10-100 μm.
Preferably, the perforation density of the anode active material layer of at least one surface of the anode current collector is 6 to 500pt/mm 2 。
Through controlling aperture, hole depth, perforation density, guarantee that positive negative pole active material layer reaches suitable tortuosity, can play effectual regulation effect to the transmission of lithium ion between positive negative pole piece through tortuosity, guarantee simultaneously that positive negative pole active coating can not cause active material to take place obvious droing, collapse owing to the pore-forming, ensure the structural stability of positive negative pole piece.
Examples
Example 1
1. Preparation of negative electrode plate
Weighing graphite serving as a cathode active material with particle diameters of 5 mu m and 10 mu m as particles of a bottom active material layer and particles of a surface active material layer respectively, and mixing the graphite with acetylene black serving as a conductive agent, CMC serving as a thickening agent and SBR serving as a binding agent according to a mass ratio of 96.4:1:1.2:1.4, mixing and adding the mixture into deionized water, and stirring the mixture under the action of a vacuum stirrer until the system is uniform to obtain to-be-negative electrode slurry A (bottom layer) and negative electrode slurry B (surface layer);
uniformly coating the anode slurry A on two surfaces of an anode current collector copper foil, airing at room temperature, and transferring to an oven for continuous drying; uniformly coating the negative electrode slurry B on the surface formed by the negative electrode slurry A, airing at room temperature, transferring to an oven, and continuously drying to obtain a coated negative electrode plate;
rolling and cutting the coated negative electrode plate to obtain a negative electrode plate, wherein the thickness of an active material layer of the negative electrode plate is 122 mu m, and mechanically punching the negative electrode plate to obtain round holes with the aperture of 10 mu m, the hole depth of 40 mu m and the punching density of 220pt/mm 2 And the tortuosity of the negative pole piece is 5.6.
2. Preparation of positive electrode plate
The positive electrode active material, the conductive agent acetylene black and the binder PVDF are mixed according to the mass ratio of 96:2:2, adding a solvent NMP after mixing, and stirring under the action of a vacuum stirrer until the system is uniform to obtain anode slurry;
uniformly coating the positive electrode slurry on two surfaces of a positive electrode current collector aluminum foil, airing at room temperature, transferring to an oven for continuous drying, cold pressing and cutting to obtain a positive electrode active material layer with 106 mu m, wherein the solid density of the positive electrode active material layer is 3.2g/cm 3 And the tortuosity of the positive pole piece is 4.1.
3. Preparation of electrolyte
Ethylene Carbonate (EC), methyl ethyl carbonate (EMC) and diethyl carbonate (DEC) are mixed according to the volume ratio of 1:1:1, mixing to obtain an organic solvent, and then drying the lithium salt LiPF sufficiently 6 Dissolving in the mixed organic solvent to prepare the electrolyte with the concentration of 1 mol/L.
4. Preparation of a separator film
Selected from polyethylene films as barrier films.
5. Preparation of lithium ion batteries
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 ion battery.
Examples 2 to 14
In the process of preparing lithium ion batteries in examples 2 to 14 and comparative examples 1 to 7, the thickness of the anode active material layer, the particle diameter of the anode surface bottom active material layer, the particle diameter of the surface active material layer, the pore diameter, the pore depth, the punching density, the tortuosity of the anode sheet, the thickness of the cathode active material layer, the compacted density of the cathode active material layer, and the tortuosity value of the cathode sheet are shown in table 1.
TABLE 1
Detection method
1. Bottom layer particle size and surface layer particle size test
The lithium batteries in examples 1 to 14 and comparative examples 1 to 7 were disassembled to obtain negative electrode sheets, the negative electrode sheets were immersed in DMC for 48 hours, the DMC was replaced every 24 hours, the cleaned negative electrode sheets were dried in an oven at 70 ℃ for 2 hours, the residual DMC solvent was removed, then the negative electrode sheets were placed in an argon ion polisher, the samples were cut using an ion beam, SEM tests were performed on the cut samples, particles were selected, and the particle size of the materials was measured.
When selecting particles, the particles constituting the underlying active material may be selected from the anode active material layer near the surface of the anode current collector, specifically, may be selected from the area from the surface of the anode current collector to 30% or less of the thickness of the anode active material layer in the anode active material layer;
in selecting the particles, the particles constituting the surface layer active material may be selected from the anode active material layer near the surface of the anode active material layer, specifically, may be selected from the area from the surface of the anode active material layer to 30% or less of the thickness of the anode active material layer in the anode active material layer.
2. Tortuosity test method
The positive and negative electrode sheets prepared in examples 1 to 14 and comparative examples 1 to 7 were respectively subjected to a tortuosity test, and the electrode sheets were subjected to pretreatment before the test: and (3) adjusting the battery to be tested to 0% SOC, disassembling the battery in a disassembly room, immersing the pole piece in DMC for 48h after disassembly, replacing DMC every 24h, placing the cleaned pole piece in a drying oven at 70 ℃ for drying for 2h, and removing residual DMC solvent.
(1) Ion impedance R ion Is characterized by comprising the following steps: (1) taking the processed negative electrode plate, and measuring the thickness of the electrode plate; cutting into pole pieces with the size of 60X 75mm and solid electrodes with the size of 60X 45mm, drying, laminating, assembling and injecting liquid according to normal procedures; (2) standing for 12h to fully wet the pole piece; (3) the upper glass clamping plate is 0.07MPa; (4) EIS test: the working electrode and the counter electrode are clamped between two polar ears, and the test frequency is 0.1-10 6 Hz,5mV perturbation. Fixed frequency spotting: at characteristic frequency (45 degree diagonal point is characteristic frequency), Z 1 Real axis intersection point =a: z is Z 2 =0，Z 1 =b; ion impedance is according to the following formulaAnd (3) calculating to obtain: r is R ion =3×(A-B)。
(2) The method for testing the porosity epsilon of the pole piece comprises the following steps: (1) sample pretreatment, a pretreatment method performed by a reference pole piece: the surface is smooth, no material is dropped, and no wrinkles are generated; (2) cutting the pole piece into a wafer with the diameter of 19mm, and simultaneously respectively measuring the thickness h of the pole piece and the current collector by using a thickness gauge 1 And h 2 The method comprises the steps of carrying out a first treatment on the surface of the The mass of the small wafer is weighed by an analytical balance and recorded as m 1 The method comprises the steps of carrying out a first treatment on the surface of the (3) Calculating the volume of the cut pole piece:the method comprises the steps of carrying out a first treatment on the surface of the (4) Immersing the pole piece in a hexadecane closed container with a certain volume for 1h; (5) taking out the soaked pole piece, sucking the surface liquid of the pole piece by filter paper until the mass of the pole piece is constant, and weighing the pole piece with the mass of m 2 The method comprises the steps of carrying out a first treatment on the surface of the (6) According to the formula:wherein ρ= 0.7734g/cm 3 。
(3) And calculating the tortuosity of the positive and negative plates according to the following formula:and the tortuosity of the positive and negative plates is recorded in table 1;
wherein R is ion Is ion resistance, A is the area of the pole piece (consistent with the area of the pole piece used in testing ion resistance), d is the thickness of the active material layer (d is the thickness of a single-layer active material layer when the pole piece is single-sided coated, d is the total thickness of double-layer active material layers when the pole piece is double-sided coated), sigma int The intrinsic conductivity of the electrolyte is 7.9mS/cm, and epsilon is the porosity of the pole piece.
3. DCR test
The lithium batteries prepared in examples 1 to 14 and comparative examples 1 to 7 were subjected to DCR test as follows:
(1) Discharging the battery to a discharge termination voltage specified in a technical document at 1C/1C in a constant temperature oven at 25 ℃ after heat balance is achieved, placing the battery at rest for not less than 10min, then charging the battery to the termination voltage at a constant current of 1C/1C, then turning to constant voltage charge, stopping charging when the charge termination current is reduced to 0.05C, and placing the battery at rest for not less than 10min after charging;
(2) Regulating charge to 80% SOC, standing for 2 hr, and recording open circuit voltage V 0 ；
(3) At 1C/1C current I D Discharging for 18s with sampling interval of 0.1s, recording 18s voltage V 18D ；
(4) Standing for 40s, sampling interval of 0.1s, and recording voltage V 1 ；
(5) At 1C/1C current I C Charging for 10s, sampling interval of 0.1s, recording voltage V of 10s 10C Standing for 10min;
(6) Discharging the battery to 50% soc at 1C/1C;
(7) Repeating steps (3) - (6);
(8) Discharging the battery to 20% soc at 1C/1C;
(9) Repeating steps (3) - (6);
the DCR value is calculated according to the following formula: internal discharge resistance (mΩ) = (V) 18s 18D - V 0 ）/I C X 1000 and recorded in table 2.
4. Cycle performance test
The lithium batteries prepared in examples 1 to 14 and comparative examples 1 to 7 were subjected to cycle performance test as follows: the prepared lithium ion battery was charged at 1C rate and discharged at 2C rate at 25C, and a full charge discharge cycle test was performed, and 1000-week cycle capacity retention rates were recorded in table 2.
TABLE 2
In combination with example 2, comparative examples 1-6, table 1 and Table 2, it can be seen that when T 2 And T 1 Not satisfying the ratio of 0.7 < T 2 /T 1 When < 1.8, no matter T 1 Whether or not T is equal to or less than 4 1 < 9 or/and T 2 Whether or not to satisfy 3 < T 2 < 10, the internal resistance and cycle performance of the lithium ion battery constructed of the positive and negative electrode materials are remarkably reduced due to the fact thatThe diffusion speed of lithium ions in the positive pole piece is far faster than that of the negative pole, if the tortuosity T of the positive pole piece and the negative pole piece is higher 2 /T 1 At less than or equal to 0.7, lithium ions are accumulated on the surface of the negative electrode more rapidly to generate lithium precipitation; when T is 2 /T 1 When the positive pole tortuosity is larger than or equal to 1.8, the charging capacity in the constant current stage is reduced and the charging constant current ratio is reduced when the high-rate charging is performed; meanwhile, the negative electrode has too small tortuosity, so that the contact area between the negative electrode and electrolyte is increased, side reactions are increased, and the circulation and storage performances are deteriorated; so when the ratio of the positive pole to the negative pole tortuosity satisfies 0.7 < T 2 /T 1 When the temperature is less than 1.8, the stability of the anode material and the cathode material can be ensured, and the excellent cycle performance of the battery can be endowed.
It can be seen from a combination of examples 1 to 8, tables 1 and 2 that T was caused by controlling the pore diameter, the pore depth, the punching density, and the compacted density of the positive electrode active material layer of the negative electrode pores 1 And T 2 The numerical values are within the respective value ranges, and T 2 And T 1 The ratio of (2) satisfies 0.7 < T 2 /T 1 Less than 1.8, even satisfies 0.85.ltoreq.T 2 /T 1 When the internal resistance of the battery is less than or equal to 1.65, the battery has small internal resistance and excellent cycle performance; the cathode material and the anode material are matched cooperatively to form a stable matching system, so that lithium ions are prevented from being enriched on the surface of the anode while being rapidly transferred, and good electrochemical environment around each particle in the electrode can be effectively ensured.
It can be seen by combining examples 2, 9-13, tables 1 and 2 that even T 2 And T 1 The ratio of (2) satisfies 0.7 < T 2 /T 1 Less than 1.8, even satisfies 0.85.ltoreq.T 2 /T 1 Not more than 1.65, however, when T 1 Not satisfy 4 is less than or equal to T 1 < 9 or/and T 2 Not satisfy 3 < T 2 When the temperature is less than 10, the lithium battery obtained by matching the anode material and the cathode material still shows the trend of increasing internal resistance and decreasing cycle performance; this is because, on the premise that the tortuosity of the active material layers of the positive and negative electrodes does not meet the value ranges of the tortuosity of the positive and negative electrodes, when the tortuosity of the positive electrode is too small, lithium ions rapidly come out from the positive electrode to reach the surface of the negative electrode under the condition of large current, so that more lithium ions are accumulated and cannot be rapidly intercalatedThe cathode is added, so that the polarization degree of the lithium battery is larger, and the battery capacity can not be fully exerted; when the tortuosity of the positive electrode is overlarge, the lithium ions are not easy to rapidly escape, the impedance of the positive electrode ions is larger, and the overall dynamic performance of the battery is poor; when the tortuosity of the negative electrode is overlarge, lithium ions cannot reach the inside of the negative electrode at a higher speed after reaching the surface of the negative electrode, the polarization is larger, the lithium separation risk exists, substances close to the current collector of the negative electrode cannot be fully utilized, meanwhile, the structure of the surface active substances is damaged due to long-term overcharge and discharge, and the capacity of the lithium battery is seriously attenuated; when the tortuosity of the negative electrode is too small, the lithium ions are inserted into the negative electrode to cause the pole piece to expand rapidly, so that the side reaction is more and the capacity attenuation is quicker; all of the above negatively affects the cycle performance of the lithium battery.
In combination with example 2, comparative example 1, example 14, comparative example 7, table 1 and table 2, it can be seen that when the thickness of the active material layer on the positive electrode and the negative electrode is large, the lithium ion transmission path is lengthened due to the increase of the thickness of the electrode sheet, the wettability of the electrode sheet is deteriorated, the concentration of lithium ions is gradually reduced from the side far from the current collector to the side near the current collector at a high current, the concentration polarization is large, a large amount of lithium ions are accumulated on the surface of the negative electrode to precipitate lithium, and meanwhile, the active material near the current collector almost cannot participate in electrochemical reaction, so that the battery capacity cannot be normally exerted, the active material outside the electrode sheet is deeply charged and discharged, the active material structure is destroyed by long-term circulation, and the battery capacity is attenuated; by controlling T 2 /T 1 The ratio of (2) satisfies 0.7 < T 2 /T 1 The improvement rate of the cycle performance of the thick electrode lithium battery is 14.5 percent less than 1.8, which is obviously higher than that of the thin electrode lithium battery by 8.4 percent.
The present embodiment is only for explanation of the present application and is not to be construed as limiting the present application, and modifications to the present embodiment, which may not creatively contribute to the present application as required by those skilled in the art after reading the present specification, are all protected by patent laws within the scope of claims of the present application.
Claims (7)
1. A lithium ion battery, characterized in that: comprises a positive electrode and a negative electrode, wherein the negative electrode comprises a negative electrodeA negative electrode active material layer provided on a surface of the negative electrode current collector; the positive electrode comprises a positive electrode current collector and a positive electrode active material layer arranged on the surface of the positive electrode current collector, wherein the compaction density Cd of the positive electrode active material layer is 2.8g/cm 3 ≤Cd≤3.8g/cm 3 The thickness of the positive electrode active material layer is 88-160 mu m; wherein the positive electrode active material layer has a tortuosity T 2 Tortuosity T with the negative electrode active material layer 1 Is 0.7 < T 2 /T 1 < 1.8; the tortuosity of the positive electrode active material layer is 3 < T 2 < 10; the tortuosity of the anode active material layer is not less than 4 and not more than T 1 ＜9；
Wherein the tortuosity of the positive electrode active material layer satisfies the following formula:
the method comprises the steps of carrying out a first treatment on the surface of the Wherein the R is ion2 An ion impedance for the positive electrode; the A is 2 The area of the pole piece of the positive electrode, namely the area of the pole piece used for testing the ion impedance of the positive electrode; said d 2 Is the total thickness of the positive electrode active material layer; the sigma int Is the intrinsic conductivity of the electrolyte; said epsilon 2 Porosity of the positive electrode;
wherein the tortuosity of the anode active material layer satisfies the following formula:
the method comprises the steps of carrying out a first treatment on the surface of the Wherein the R is ion1 An ionic impedance for the negative electrode; the A is 1 The electrode plate area of the negative electrode, namely the electrode plate area used in the process of testing the ion impedance of the negative electrode; said d 1 Is the total thickness of the anode active material layer; the sigma int Is the intrinsic conductivity of the electrolyte; said epsilon 1 Is the porosity of the negative electrode.
2. A lithium ion battery according to claim 1 whichIs characterized in that: tortuosity T of the positive electrode active material layer 2 Tortuosity T with the negative electrode active material layer 1 The ratio of (2) satisfies 0.85.ltoreq.T 2 /T 1 ≤1.65。
3. A lithium ion battery according to claim 1, wherein: the negative electrode active material layer has a thickness of 90-220 μm.
4. A lithium ion battery according to claim 1, wherein: the positive electrode active material layer has a thickness of 105 to 160 μm and/or the negative electrode active material layer has a thickness of 120 to 220 μm.
5. A lithium ion battery according to claim 1, wherein: the negative electrode active material layer of at least one surface of the negative electrode current collector includes a bottom active material layer close to the negative electrode current collector and a surface active material layer far from the negative electrode current collector; the particle size of the particles constituting the bottom active material layer satisfies D50 of 5 μm or less and 9 μm or less, and the particle size of the particles constituting the surface active material layer satisfies D50 of 10 μm or less and 15 μm or less.
6. A lithium ion battery according to claim 1, wherein: holes are formed in the negative electrode active material layer on at least one surface of the negative electrode current collector, the ratio of the depth of the holes to the thickness of the negative electrode active material layer in the negative electrode active material layer is 0.09-0.96, and the pore diameter of the holes is 2-80 μm.
7. The lithium ion battery of claim 6, wherein: the negative electrode active material layer on at least one surface of the negative electrode current collector has a perforation density of 6-500pt/mm 2 。
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| CN114649500A (en) * | 2022-04-01 | 2022-06-21 | 宁德新能源科技有限公司 | Negative electrode plate, electrochemical device and electronic equipment |
| CN114865063A (en) * | 2022-06-14 | 2022-08-05 | 天津市捷威动力工业有限公司 | Lithium ion battery, evaluation method of lithium ion battery, battery module and vehicle |
| CN115050923A (en) * | 2021-03-31 | 2022-09-13 | 宁德新能源科技有限公司 | Electrochemical device and electronic device |
| CN115566255A (en) * | 2022-10-27 | 2023-01-03 | 欣旺达电动汽车电池有限公司 | Secondary battery and electric equipment |
| CN115799441A (en) * | 2023-02-10 | 2023-03-14 | 欣旺达电动汽车电池有限公司 | Lithium ion battery and power utilization device |
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| CN115050923A (en) * | 2021-03-31 | 2022-09-13 | 宁德新能源科技有限公司 | Electrochemical device and electronic device |
| CN114649500A (en) * | 2022-04-01 | 2022-06-21 | 宁德新能源科技有限公司 | Negative electrode plate, electrochemical device and electronic equipment |
| CN114865063A (en) * | 2022-06-14 | 2022-08-05 | 天津市捷威动力工业有限公司 | Lithium ion battery, evaluation method of lithium ion battery, battery module and vehicle |
| CN115566255A (en) * | 2022-10-27 | 2023-01-03 | 欣旺达电动汽车电池有限公司 | Secondary battery and electric equipment |
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