Lithium-ion battery and electric device

Abstract

A lithium-ion battery and an electric device. The lithium-ion battery comprises a positive electrode sheet, a negative electrode sheet, and an electrolyte, wherein the positive electrode sheet comprises a positive electrode active material, and a lithium-ion solid-phase diffusion characteristic time constant of the positive electrode active material is Tp; and the negative electrode sheet comprises a negative electrode active material, and a lithium-ion solid-phase diffusion characteristic time constant of the negative electrode active material is Tn, wherein Tp and Tn satisfy: 0.01≤Tp / Tn≤6. The lithium-ion solid-phase diffusion characteristic time constant T of the active material is defined as T＝(L / 2)2 / D, and the unit thereof is seconds, wherein L is the volume distribution particle size Dv50 of the active material, and the unit thereof is μm, and D is the lithium-ion solid-phase diffusion coefficient of the active material, and the unit thereof is μm2 / s.

Description

Lithium-ion batteries and electrical devices

[0001] Cross-references

[0002] This application refers to Chinese Patent Application No. 2024102694241, filed on March 8, 2024, entitled “Lithium-ion Battery and Electrical Device,” which is incorporated herein by reference in its entirety. Technical Field

[0003] The present application relates to the technical field of secondary batteries, and in particular to a lithium-ion battery and an electrical device. Background Art

[0004] In recent years, secondary batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields.

[0005] With the popularization of secondary battery applications, higher requirements are placed on their fast charging performance under high-rate charging conditions. Summary of the Invention

[0006] The present application is made in view of the above-mentioned problems, and its purpose is to provide a lithium-ion battery, characterized in that the lithium-ion battery includes a positive electrode plate, a negative electrode plate and an electrolyte; wherein the positive electrode plate includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector, the positive electrode film layer includes a positive electrode active material, and the lithium ion solid phase diffusion characteristic time constant of the positive electrode active material is Tp; the negative electrode plate includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, the negative electrode film layer includes a negative electrode active material, and the lithium ion solid phase diffusion characteristic time constant of the negative electrode active material is Tn, and Tp and Tn satisfy: 0.01≤Tp / Tn≤6, wherein the lithium ion solid phase diffusion characteristic time constant of the active material is T=(L / 2) 2 / D, in seconds, where L is the volume distribution particle size Dv50 of the active material, in μm, and D is the lithium ion solid phase diffusion coefficient of the active material, in μm 2 / s.

[0007] The lithium ion diffusion rate of the secondary battery with the characteristic time constant of the lithium ion solid phase diffusion within the above range is equivalent on the negative electrode side and the positive electrode side, so that the positive and negative electrode kinetic performances of the secondary battery are matched, the electrochemical performance of the secondary battery under high-rate charge and discharge conditions is improved, the probability of lithium ion precipitation at the negative electrode is reduced, and the capacity loss under high-rate charge and discharge conditions is reduced.

[0008] In any embodiment, 0.1≤Tp / Tn≤5.5.

[0009] The rate performance of the secondary battery with the characteristic time constant of lithium ion solid phase diffusion within the above range can be further improved, that is, the capacity loss under high rate charge and discharge conditions is reduced and the cycle stability is increased.

[0010] In any embodiment, 1×10s≤Tp≤5×10 3 s, the unit is seconds.

[0011] In any embodiment, 2s≤Tn≤3×10 4 s, the unit is seconds.

[0012] Secondary batteries with a lithium ion solid phase diffusion characteristic time constant within the above range have good kinetic performance and still have good electrochemical performance under fast charging conditions.

[0013] In any embodiment, the lithium ion solid phase diffusion coefficient of the positive electrode active material is Dp, the lithium ion solid phase diffusion coefficient of the negative electrode active material is Dn, and Dp and Dn satisfy: Dn>Dp.

[0014] Compared with the positive electrode active material, the negative electrode active material has a higher lithium ion solid phase diffusion coefficient, which makes the lithium ions have a higher diffusion rate in the negative electrode, which can greatly reduce the risk of lithium plating and improve the safety performance of lithium-ion batteries.

[0015] In any embodiment, the volume distribution particle size Dv50 of the positive electrode active material is Lp, the volume distribution particle size Dv50 of the negative electrode active material is Ln, and Lp and Ln satisfy: Ln>Lp.

[0016] The combination of a small particle size and a relatively high lithium ion diffusion coefficient of the negative electrode active material can better balance the lithium ion solid phase diffusion characteristic time constants of the negative electrode active material and the positive electrode active material, achieve mutual matching between the two, and reduce the loss of secondary battery capacity under fast charging conditions.

[0017] In any embodiment, 5 μm ≤ Ln ≤ 20 μm.

[0018] In any embodiment, 7 μm ≤ Ln ≤ 15 μm.

[0019] In any embodiment, the positive electrode active material includes a lithium-containing phosphate material, and the volume distribution particle size Dv50 of the positive electrode active material satisfies: 0.3 μm≤Lp≤2 μm.

[0020] In any embodiment, the positive electrode active material comprises a lithium-containing transition metal oxide, and the volume distribution particle size Dv50 of the positive electrode active material satisfies: 2 μm≤Lp≤10 μm.

[0021] In any embodiment, the liquid phase diffusion characteristic time constant of the positive electrode plate is Tep, and Tep and Tp satisfy: 0.0001≤Tep / Tp≤60, optionally 0.01≤Tep / Tp≤50, wherein the liquid phase diffusion characteristic time constant of the plate Where Le is the thickness of the film on the current collector side, in μm; De is the liquid phase diffusion coefficient at room temperature, in μm 2 / s; ε is the porosity of the membrane layer.

[0022] A secondary battery in which the ratio of the liquid-phase diffusion characteristic time constant to the solid-phase diffusion characteristic time constant of the positive electrode plate is within the above range can achieve matching of the liquid-phase diffusion time and the solid-phase diffusion time of lithium ions in the positive electrode plate, further reducing the risk of rate performance deterioration or lithium plating due to polarization, improving the electrochemical performance of the secondary battery after fast charging, and reducing the capacity loss after fast charging.

[0023] In any embodiment, Tep satisfies: 3s≤Tep≤3×10 5 s, the unit is seconds.

[0024] The secondary battery with the liquid phase diffusion characteristic time constant of the positive electrode plate within the above range has good kinetic performance and still has good electrochemical performance under fast charging conditions.

[0025] In any embodiment, the liquid phase diffusion characteristic time constant of the negative electrode plate is Ten, and Ten and Tn satisfy: 0.0004≤Ten / Tn≤70, and can be optionally 0.001≤Ten / Tn≤60.

[0026] A secondary battery in which the ratio of the liquid-phase diffusion characteristic time constant to the solid-phase diffusion characteristic time constant of the negative electrode plate is within the above range can achieve matching of the liquid-phase diffusion time and the solid-phase diffusion time of lithium ions in the negative electrode plate, reduce the probability of lithium precipitation in the negative electrode plate, and improve the safety performance and cycle life of the secondary battery.

[0027] In any embodiment, Ten satisfies: 4s≤Ten≤2×10 5 s, the unit is seconds.

[0028] The secondary battery with the liquid phase diffusion characteristic time constant of the negative electrode plate within the above range has good kinetic performance and still has good electrochemical performance under fast charging conditions.

[0029] In any embodiment, the secondary battery includes an electrolyte, and the conductivity of the electrolyte at room temperature is 0.6 S / m-2 S / m, and optionally 1.0 S / m-1.8 S / m.

[0030] The electrolyte with a conductivity within the above range at room temperature has a higher liquid phase diffusion coefficient, which is beneficial to the improvement and optimization of the kinetic performance of the secondary battery.

[0031] In any embodiment, the electrolyte includes a linear carboxylate solvent, and the linear carboxylate solvent includes one or two of ethyl acetate, methyl acetate, methyl formate, butyl acetate, methyl propionate, ethyl propionate, methyl butyrate, propyl butyrate, butyl butyrate, isopropyl acetate and isoamyl acetate.

[0032] The linear carboxylate solvent imparts lower viscosity and higher conductivity to the electrolyte, thereby increasing the liquid-phase diffusion coefficient and reducing the liquid-phase characteristic time constant. In any embodiment, the linear carboxylate solvent comprises 5%-80% by weight of the total mass of the electrolyte, optionally 10%-70%. In any embodiment, the thickness of the positive electrode film layer on the current collector side is 32μm-122μm; and / or the porosity of the positive electrode film layer is 15%-50%.

[0033] In any embodiment, the thickness of the negative electrode film layer on the current collector side is 29 μm-77 μm; and / or the porosity of the negative electrode film layer is 20%-60%.

[0034] The electrode film thickness and porosity within the above ranges have a suitable liquid phase diffusion characteristic time constant Te, which is conducive to balancing the dynamic performance and energy density of the secondary battery. The second aspect of the present application provides an electrical device including the lithium ion battery of the first aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] FIG1 is a schematic diagram of a secondary battery according to an embodiment of the present application;

[0036] FIG2 is an exploded view of the secondary battery according to one embodiment of the present application shown in FIG1 ;

[0037] FIG3 is a schematic diagram of a battery module according to an embodiment of the present application;

[0038] FIG4 is a schematic diagram of a battery pack according to an embodiment of the present application;

[0039] FIG5 is an exploded view of the battery pack according to an embodiment of the present application shown in FIG4 ;

[0040] FIG6 is a schematic diagram of an electric device using a secondary battery as a power source according to an embodiment of the present application.

[0041] Explanation of reference numerals: 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 secondary battery; 51 housing; 52 electrode assembly; 53 cover plate. DETAILED DESCRIPTION

[0042] Below, the embodiments of the lithium-ion battery and the electrical device of the present application are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the drawings and the following description are provided to enable those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0043] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0044] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0045] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0046] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0047] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0048] Unless otherwise specified, the term "or" is used in this application to be inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0049] Compared to traditional fuel vehicles, range anxiety and long charging times are major obstacles hindering the development of electric vehicles. Increasing the charge rate can reduce the charging time of secondary batteries, but at high charging currents, the charge capacity and cycle life of secondary batteries often drop significantly; some batteries even experience lithium deposition, posing a safety hazard. Therefore, improving the fast charging capability of batteries has become a focus for battery manufacturers and automakers. How to effectively improve the charge capacity and cycle stability of secondary batteries at high charging currents to enhance their fast charging performance is a pressing technical issue in this field.

[0050] [Lithium-ion battery]

[0051] Based on this, the present application provides a lithium-ion battery, which includes a positive electrode sheet, a negative electrode sheet and an electrolyte; wherein the positive electrode sheet includes a positive electrode active material, and the lithium ion solid phase diffusion characteristic time constant of the positive electrode active material is Tp,

[0052] The negative electrode plate includes a negative electrode active material, and the lithium ion solid phase diffusion characteristic time constant of the negative electrode active material is Tn.

[0053] And Tp and Tn satisfy: 0.01≤Tp / Tn≤6,

[0054] Among them, the characteristic time constant of lithium ion solid phase diffusion of active material is T = (L / 2) 2 / D, in seconds, where L is the volume distribution particle size Dv50 of the active material, in μm, and D is the lithium ion solid phase diffusion coefficient of the active material, in μm2 / s.

[0055] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, the positive electrode film layer including a positive electrode active material. In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, the negative electrode film layer including a negative electrode active material.

[0056] The characteristic time constant T of the solid phase diffusion of lithium ions in the active material can be calculated by testing the volume distribution particle size Dv50 of the active material and the lithium ion solid phase diffusion coefficient D of the active material respectively, and then using the above formula to calculate the characteristic time constant T of the solid phase diffusion of lithium ions in the active material. The solid phase diffusion coefficient can be obtained by testing using the potential relaxation method. The specific test method and calculation process of the potential relaxation method are as follows. The definition of potential relaxation can be expressed as studying the relationship between the electrode potential and time under the premise that there is no material and energy exchange between the battery and the outside world. It is used to analyze the potential change during the relaxation process and is obtained by testing under constant current discharge to a certain capacity. The potential relaxation formula is shown in Formula I:

[0057] in is the equilibrium electrode potential, is the initial potential, R is the gas constant, which is 8.31 J / (mol×K), T is the temperature, in K, L is the volume distribution particle size Dv50 of the active material, in μm; D is the lithium ion solid phase diffusion coefficient of the active material, in μm 2 / s; t is the time when the electrode potential reaches equilibrium, in seconds; F is the Faraday constant, which is 96500 C / mol, and lnN is the intercept of the ordinate.

[0058] The specific test process is as follows: prepare a three-electrode cell by taking the electrode and the acid-treated copper wire, discharge the cell at a constant current of 0.33C to 50% of the charge state, let it stand for 15 minutes, then discharge it at a constant current of 1C for 60 seconds, cut off the current, record the curve of the cathode and anode potential changing with time during this process, and then make a The curve is fitted linearly to the part of the curve that shows a stable linear relationship, and the slope is obtained to obtain the value of the solid phase diffusion coefficient of the active material.

[0059] It can be understood that the solid phase diffusion characteristic time constant of the positive electrode active material is Tp = (Lp / 2) 2 / Dp, Lp is the volume distribution particle size Dv50 of the positive electrode active material, Dp is the lithium ion solid phase diffusion coefficient of the positive electrode active material, and the three-electrode cell prepared with the positive electrode plate, acid-treated copper wire and reference electrode in the secondary battery can be used to test the lithium ion solid phase diffusion coefficient Dp of the positive electrode active material by potential relaxation method, and then the solid phase diffusion characteristic time constant Tp of the positive electrode active material can be obtained by calculation. The solid phase diffusion characteristic time constant Tn of the negative electrode active material is (Ln / 2) 2 / Dn; Ln is the volume distribution particle size Dv50 of the negative electrode active material, Dn is the lithium ion solid phase diffusion coefficient of the negative electrode active material, and a three-electrode battery cell prepared with the negative electrode plate in the secondary battery, the acid-treated copper wire and the reference electrode can be used to test the lithium ion solid phase diffusion coefficient Dn of the negative electrode active material by the potential relaxation method, and then the solid phase diffusion characteristic time constant Tn of the negative electrode active material is obtained by calculation.

[0060] The charging reaction of lithium-ion batteries mainly includes the solid-phase diffusion of lithium in the positive electrode sheet particles, the interfacial transfer at the positive electrode sheet-electrolyte interface, the liquid-phase transport in the electrolyte, the interfacial transfer at the electrolyte-negative electrode sheet interface, and the solid-phase diffusion of lithium in the negative electrode sheet particles. Due to the slow solid-phase diffusion rate, solid-phase diffusion is often the rate-controlling step of the electrochemical reaction and has a key influence on the kinetic performance of secondary batteries. The diffusion process of lithium in the solid phase is complex, including but not limited to embedding / de-embedding, alloying / de-alloying, etc., including the diffusion of the "transposition mechanism" in the ionic crystal, the diffusion affected by the concentration gradient, and the diffusion affected by the chemical potential. Taking the concentration gradient effect as an example, in lithium-ion batteries, lithium ions are de-embedded from the surface of the active material particles. Therefore, a lithium ion concentration gradient will appear inside the particles of the active material. Driven by this concentration gradient, Li + Diffusion within the active particles. The solid-phase lithium ion diffusion coefficient, D, is a macroscopic concept encompassing the aforementioned diffusion processes and serves as a parameter characterizing the diffusion rate and kinetic behavior of a material. Generally speaking, the larger the solid-phase lithium ion diffusion coefficient, D, the greater the lithium ion diffusion rate within the active material. The "lithium ion solid-phase diffusion characteristic time constant, T, of the active material" can be used to measure the time required for lithium ions to diffuse into and out of the electrode active material.

[0061] In some embodiments, Tp / Tn can be selected as 0.01, 0.1, 1, 2, 3, 4, 5, 6, or any range therebetween.

[0062] The characteristic time constant of the solid-phase diffusion of lithium ions in the active material can be used to characterize the length of time required for the solid-phase diffusion of lithium ions in the positive and negative electrodes. A secondary battery with a characteristic time constant of the solid-phase diffusion of lithium ions within the above range will not experience a situation where the rate of lithium ion embedding on the negative electrode side cannot keep up with the rate of lithium ion extraction on the positive electrode side under fast charging conditions due to the fact that the solid-phase diffusion time of lithium ions on the negative electrode side is too long compared to the solid-phase diffusion time of lithium ions on the positive electrode side, causing lithium ion enrichment on the surface of the negative electrode side, leading to lithium precipitation and safety hazards. Furthermore, a situation where the number of lithium ions embedded on the negative electrode side during charging is too small due to the fact that the solid-phase diffusion time of lithium ions on the positive electrode side is too long compared to the solid-phase diffusion time of lithium ions on the negative electrode side, causing the discharge capacity of the secondary battery under fast charging conditions to drop significantly compared to the rated capacity will not occur. The lithium ion diffusion rate of the secondary battery with the characteristic time constant of the lithium ion solid phase diffusion within the above range is equivalent on the negative electrode side and the positive electrode side, so that the positive and negative electrode kinetic performances of the secondary battery are matched, the electrochemical performance of the secondary battery under high-rate charge and discharge conditions is improved, the probability of lithium ion precipitation at the negative electrode is reduced, and the capacity loss under high-rate charge and discharge conditions is reduced.

[0063] In some embodiments, 0.1≤Tp / Tn≤5.5.

[0064] A secondary battery with a lithium ion solid phase diffusion characteristic time constant within the above range can further improve the fast charging performance of the secondary battery.

[0065] In some embodiments, 1×10s≤Tp≤5×10 3 s, the unit is seconds.

[0066] In some embodiments, Tp can be selected from 1×10s, 2×10s, 3×10s, 4×10s, 5×10s, 6×10s, 7×10s, 8×10s, 9×10s, 1×10 2 s, 2×10 2 s, 3×10 2 s, 4×10 2 s, 5×10 2 s, 6×10 2 s, 7×10 2 s, 8×10 2 s, 9×10 2 s, 1×10 3 s, 2×10 3 s, 3×10 3 s, 4×10 3 s, 5×10 3 s or any range of values ​​between them.

[0067] In some embodiments, 2s≤Tn≤3×10 4s, the unit is seconds.

[0068] In some embodiments, Tn can be selected from 2s, 3s, 4s, 5s, 6s, 7s, 8s, 9s, 1×10s, 2×10s, 3×10s, 4×10s, 5×10s, 6×10s, 7×10s, 8×10s, 9×10s, 2×10 2 s, 3×10 2 s, 4×10 2 s, 5×10 2 s, 6×10 2 s, 7×10 2 s, 8×10 2 s, 9×10 2 s, 1×10 3 s, 2×10 3 s, 3×10 3 s, 4×10 3 s, 5×10 3 s, 6×10 3 s, 7×10 3 s, 8×10 3 s, 9×10 3 s, 1×10 4 s, 2×10 4 s, 3×10 4 s or any range of values ​​between them.

[0069] Secondary batteries with a lithium ion solid phase diffusion characteristic time constant within the above range have good kinetic performance and still have good electrochemical performance under fast charging conditions.

[0070] In some embodiments, the lithium ion solid phase diffusion coefficient of the positive electrode active material is Dp, the lithium ion solid phase diffusion coefficient of the negative electrode active material is Dn, and Dp and Dn satisfy: Dn>Dp.

[0071] The solid-phase lithium-ion diffusion coefficient (D) is an important indicator of diffusion speed. Its academic definition can be expressed as the diffusion and mass transfer rate of particles under a unit concentration gradient. In this application, the solid-phase lithium-ion diffusion coefficient can be measured using the potential relaxation method. For specific testing methods, refer to the testing process for the "Characteristic time constant T of lithium-ion solid-phase diffusion of active materials" above.

[0072] Compared with the positive electrode active material, the negative electrode active material has a higher lithium ion solid phase diffusion coefficient, which makes the lithium ions have a higher diffusion rate in the negative electrode, which can greatly reduce the risk of lithium plating and improve the safety performance of lithium-ion batteries.

[0073] In some embodiments, the volume distribution particle size Dv50 of the positive electrode active material is Lp, the volume distribution particle size Dv50 of the negative electrode active material is Ln, and Lp and Ln satisfy: Ln>Lp.

[0074] In this application, the volume distribution particle size Dv50 of the active material is generally known in the art and represents the particle size corresponding to the cumulative volume distribution percentage of the material reaching 50%. It can be measured using instruments and methods known in the art. For example, it can be measured using a laser particle size analyzer in accordance with GB / T19077-2016. The testing instrument can be a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd. in the UK.

[0075] The combination of a small particle size and a relatively high lithium ion diffusion coefficient of the negative electrode active material can better balance the lithium ion solid phase diffusion characteristic time constants of the negative electrode active material and the positive electrode active material, achieve mutual matching between the two, and reduce the loss of secondary battery capacity under fast charging conditions.

[0076] In some embodiments, 5 μm ≤ Ln ≤ 20 μm.

[0077] In some embodiments, Ln can be selected as 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm or any range therebetween.

[0078] In some embodiments, 7 μm ≤ Ln ≤ 15 μm.

[0079] When the volume distribution particle size Dv50 of the negative electrode active material is within the above range, lithium plating can be reduced while improving the rate performance of the secondary battery.

[0080] In some embodiments, the positive electrode active material includes a lithium-containing phosphate material, and the volume distribution particle size Dv50 of the positive electrode active material satisfies: 0.3 μm≤Lp≤2 μm.

[0081] Examples of lithium-containing phosphates include, but are not limited to, at least one of lithium iron phosphate (e.g., LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (e.g., LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon. In some embodiments, Lp can be selected from 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 2 μm, or any range therebetween.

[0082] In some embodiments, the positive electrode active material comprises a lithium-containing transition metal oxide, and the volume distribution particle size Dv50 of the positive electrode active material satisfies: 2 μm≤Lp≤10 μm.

[0083] In some embodiments, Lp may be 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm or any range therebetween. Examples of lithium-containing transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2) and at least one of its modified compounds, etc.

[0084] Secondary batteries with a volume distribution particle size within the above range have good kinetic performance and still have good electrochemical performance under fast charging conditions.

[0085] The lithium ion solid phase diffusion coefficient D is closely related to the composition, defects, and structure of the active material. The positive electrode active material and / or the negative electrode active material can be adjusted in any manner to improve the lithium ion solid phase diffusion coefficient D. As an example, the lithium ion solid phase diffusion coefficient Dp of the positive electrode active material can be improved by increasing the Co content or increasing the polycrystalline ratio in the positive electrode active material; the lithium ion solid phase diffusion coefficient Dn of the negative electrode active material can be increased by reducing the graphitization degree of the negative electrode active material or increasing the thickness of the amorphous carbon coating layer of the negative electrode active material.

[0086] In some embodiments, the positive electrode active material may be a battery positive electrode active material known in the art. For example, the positive electrode active material may include at least one of the following materials: an olivine-structured lithium-containing phosphate, a lithium transition metal oxide, and modified compounds thereof. However, this application is not limited to these materials; other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used singly or in combination.

[0087] In some embodiments, the positive electrode active material includes a lithium-containing transition metal oxide, and the molar proportion of the cobalt element is 5%-20% based on the total molar number of the transition metal elements in the positive electrode active material.

[0088] In some embodiments, based on the total molar number of transition metal elements in the positive electrode active material, the molar proportion of cobalt element can be selected to be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20% or any numerical range therebetween.

[0089] In some embodiments, the negative electrode active material may be a negative electrode active material for a battery that is well known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0090] In some embodiments, the negative electrode active material includes an amorphous carbon coating layer, and the mass content of the amorphous carbon is 1%-6% based on the total mass of the negative electrode active material.

[0091] In some embodiments, the mass content of amorphous carbon can be 1%, 2%, 3%, 4%, 5%, 6% or any range therebetween, based on the total mass of the negative electrode active material.

[0092] In some embodiments, the degree of graphitization of the negative electrode active material is 88%-96%.

[0093] In some embodiments, the degree of graphitization of the negative electrode active material may be 88%, 90%, 92%, 94%, 96%, or any embodiment therebetween.

[0094] In some embodiments, the liquid phase diffusion characteristic time constant of the positive electrode plate is Tep, and Tep and Tp satisfy: 0.0001≤Tep / Tp≤60, optionally 0.01≤Tep / Tp≤50; wherein the liquid phase diffusion characteristic time constant of the plate Where Le is the thickness of the film layer on one side of the current collector, in μm; De is the liquid phase diffusion coefficient of the film layer, in μm 2 / s; ε is the porosity of the membrane layer.

[0095] When lithium ions are released from the active material particles, the lithium ion concentration in the electrolyte surrounding the active material in the electrode film increases. When lithium ions are embedded in the active material particles, the lithium ion concentration in the electrolyte surrounding the active material decreases, resulting in a concentration gradient in the electrolyte within the electrode film. Driven by this concentration gradient, lithium ions diffuse, a process known as liquid-phase diffusion. The characteristic time constant of the electrode's liquid-phase diffusion refers to the time required for lithium ions to travel through the electrolyte to the interior of the electrode.

[0096] The characteristic time constant Te of the liquid phase diffusion of the electrode can be obtained by the formula Calculated, where Le is the thickness of the electrode film on the collector side, in μm; De is the liquid phase diffusion coefficient, in μm 2 / s; ε is the porosity of the electrode film. It can be understood that the liquid phase diffusion characteristic time constant Tep of the positive electrode is calculated based on the thickness and porosity of the positive electrode film; the liquid phase diffusion characteristic time constant Ten of the negative electrode is calculated based on the thickness and porosity of the negative electrode film.

[0097] The pole piece film thickness Le can be measured by any known method in the art. As an example, a microscope (such as a Zeiss X-ray microscope Xradia610) is used to observe the pole piece cross section to test the pole piece film thickness. The liquid phase diffusion coefficient De is used to describe the free diffusion rate of lithium ions in the electrolyte. De = σ × 258 / 0.775, where σ is the conductivity of the electrolyte at 298.15K, in units of S / m. The conductivity of the electrolyte can be tested using a conductivity tester (for example, a Leici (DDSJ-318) conductivity meter). As an example, the test environment temperature is controlled to be 25°C and the ambient humidity is less than 80%. A certain amount (for example, 40 mL) of electrolyte is taken, the sample is poured into a dry and clean plastic centrifuge tube and placed in a constant temperature bath at 25°C for 30 minutes. The electrode (for example, a platinum black plate) that has been dried of moisture is placed vertically in the uniform sample to be tested, the instrument is started, and an AC voltage of 1 kHz is applied for testing. The test is repeated 3 times, and the average of the 3 results is taken as the conductivity of the electrolyte. The porosity ε of the electrode film layer can be obtained by any known method in the art. As an example, according to GB / T21650.2-2008ISO·15901-2:2006, the porosity ε of the electrode film layer is determined by nitrogen adsorption method, that is, the percentage of the pore volume of the electrode to the total volume: the calculation formula is ε = (V1-V2) / V1×100%, where V1 is the apparent volume of the sample and V2 is the actual volume of the sample. The apparent volume V1 of the sample is calculated by the formula V1 = S × H × A, where S is the area of ​​the electrode (unit: cm 2 ); H is the thickness of the electrode to be stacked (unit: cm); A is the number of sample electrodes (unit: ea). The specific test steps are as follows: In a conventional laboratory environment, use tweezers to select no less than 20 electrode discs with good appearance and no powder falling on the edges and put them into the sample cup, record the number of pieces, and calculate the apparent volume V1; put the sample electrode into a 3.5cm 3 After the sample cup is placed in the true density tester, the test system is sealed, and ammonia is introduced according to the program. By detecting the pressure of the gas in the sample chamber and the expansion chamber, the real volume V2 is calculated according to Bohr's law (PV=nRT), thereby obtaining the porosity of the electrode to be tested.

[0098] In some embodiments, Tep / Tp may be 0.0001, 0.0002, 0.001, 0.01, 0.1, 1, 10, 50, 60, or any range therebetween.

[0099] A secondary battery in which the ratio of the liquid-phase diffusion characteristic time constant to the solid-phase diffusion characteristic time constant of the positive electrode plate is within the above range can achieve matching of the liquid-phase diffusion time and the solid-phase diffusion time of lithium ions in the positive electrode plate, further reducing the risk of rate performance deterioration or lithium plating due to polarization, improving the electrochemical performance of the secondary battery after fast charging, and reducing the capacity loss after fast charging.

[0100] In some embodiments, Tep satisfies: 3s≤Tep≤3×10 5 s, the unit is seconds.

[0101] In some embodiments, Tep can be selected as 3s, 4s, 5s, 6s, 7s, 8s, 9s, 1×10s, 2×10s, 3×10s, 4×10s, 5×10s, 6×10s, 7×10s, 8×10s, 9×10s, 1×10 2 s, 2×10 2 s, 3×10 2 s, 4×10 2 s, 5×10 2 s, 6×10 2 s, 7×10 2 s, 8×10 2 s, 9×10 2 s, 1×10 3 s, 2×10 3 s, 3×10 3 s, 4×10 3 s, 5×10 3 s, 6×10 3 s, 7×10 3 s, 8×10 3 s, 9×10 3 s, 1×10 4 s, 2×10 4 s, 3×10 4 s, 4×10 4 s, 5×10 4 s, 6×10 4 s, 7×10 4 s, 8×10 4 s, 9×10 4 s, 1×10 5 s, 2×10 5 s, 3×10 5 s or any range of values ​​between them.

[0102] The secondary battery with the liquid phase diffusion characteristic time constant of the positive electrode plate within the above range has good kinetic performance and still has good electrochemical performance under fast charging conditions.

[0103] In some embodiments, the liquid phase diffusion characteristic time constant of the negative electrode plate is Ten, and Ten and Tn satisfy: 0.0004≤Ten / Tn≤70.

[0104] In some embodiments, Ten / Tn can be selected as 0.0004, 0.001, 0.01, 0.1, 1, 10, 50, 60, 70, or any range therebetween.

[0105] A secondary battery in which the ratio of the liquid-phase diffusion characteristic time constant to the solid-phase diffusion characteristic time constant of the negative electrode plate is within the above range can achieve matching of the liquid-phase diffusion time and the solid-phase diffusion time of lithium ions in the negative electrode plate, reduce the probability of lithium precipitation in the negative electrode plate or the deterioration of rate performance due to polarization, and improve the safety performance and cycle life of the secondary battery.

[0106] In some embodiments, Ten can be selected from 4s, 5s, 6s, 7s, 8s, 9s, 1×10s, 2×10s, 3×10s, 4×10s, 5×10s, 6×10s, 7×10s, 8×10s, 9×10s, 1×10 2 s, 2×10 2 s, 3×10 2 s, 4×10 2 s, 5×10 2 s, 6×10 2 s, 7×10 2 s, 8×10 2 s, 9×10 2 s, 1×10 3 s, 2×10 3 s, 3×10 3 s, 4×10 3 s, 5×10 3 s, 6×10 3 s, 7×10 3 s, 8×10 3 s, 9×10 3 s, 1×10 4 s, 2×10 4 s, 3×10 4 s, 4×10 4 s, 5×10 4 s, 6×10 4 s, 7×10 4 s, 8×10 4 s, 9×10 4 s, 1×10 5 s, 2×10 5 s or any range of values ​​between them.

[0107] The secondary battery with the liquid phase diffusion characteristic time constant of the negative electrode plate within the above range has good kinetic performance and still has good electrochemical performance under fast charging conditions.

[0108] In some embodiments, the conductivity of the electrolyte at room temperature is 0.6 S / m-2 S / m, and can be optionally 1.0 S / m-1.8 S / m.

[0109] In some embodiments, the conductivity of the electrolyte at room temperature can be selected from 0.6 S / m, 0.8 S / m, 1 S / m, 1.2 S / m, 1.4 S / m, 1.6 S / m, 1.8 S / m, 2 S / m or any range therebetween.

[0110] The electrolyte with a conductivity within the above range at room temperature has a higher liquid phase diffusion coefficient, which is beneficial to the improvement and optimization of the kinetic performance of the secondary battery.

[0111] In some embodiments, a secondary battery includes an electrolyte including a linear carboxylate solvent.

[0112] The linear carboxylate solvent makes the electrolyte have lower viscosity and higher conductivity, thereby increasing the liquid phase diffusion coefficient of the electrolyte, which is beneficial to reducing the liquid phase characteristic time constant of the electrolyte.

[0113] In some embodiments, the linear carboxylate solvent comprises one or two of ethyl acetate, methyl acetate, methyl formate, butyl acetate, methyl propionate, ethyl propionate, methyl butyrate, propyl butyrate, butyl butyrate, isopropyl acetate, and isoamyl acetate.

[0114] In some embodiments, based on the total mass of the electrolyte, the mass percentage of the linear carboxylate solvent is 5%-80%, optionally 10%-70%.

[0115] In some embodiments, based on the total mass of the electrolyte, the mass percentage of the linear carboxylate solvent can be selected as 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80% or any range therebetween.

[0116] In some embodiments, the thickness of the positive electrode film layer on the current collector side is 32 μm-122 μm.

[0117] In some embodiments, the thickness of the positive electrode film layer on the current collector side can be selected as 32 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, 122 μm or any numerical range therebetween.

[0118] In some embodiments, the porosity of the positive electrode film layer is 15%-50%.

[0119] In some embodiments, the porosity of the positive electrode film layer may be 15%, 20%, 30%, 40%, 50%, or any range of values ​​therebetween.

[0120] In some embodiments, the thickness of the negative electrode film layer on the current collector side is 29 μm-77 μm.

[0121] In some embodiments, the thickness of the negative electrode film layer on the current collector side may be 29 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 77 μm, or any range therebetween.

[0122] In some embodiments, the porosity of the negative electrode film layer is 20%-60%.

[0123] In some embodiments, the porosity of the negative electrode film layer may be 20%, 30%, 40%, 50%, 60%, or any range of values ​​therebetween.

[0124] It is understood that the porosity of the positive electrode film layer and the negative electrode film layer can be adjusted by any known method in the art, for example, the porosity of the film layer can be adjusted by adjusting the compaction density of the electrode sheet or the compaction density of the active material powder.

[0125] The electrode film with a thickness and porosity within the above range has a suitable liquid phase diffusion characteristic time constant Te, which is beneficial to taking into account both the dynamic performance and energy density of the secondary battery.

[0126] [Positive electrode]

[0127] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0128] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0129] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0130] In some embodiments, the positive electrode film layer may further include a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0131] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0132] [Negative electrode]

[0133] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0134] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0135] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0136] In some embodiments, the negative electrode film layer may further include a binder. For example, the binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0137] In some embodiments, the negative electrode film layer may further include a conductive agent. For example, the conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0138] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0139] In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0140] [Electrolyte]

[0141] In some embodiments, the electrolyte solution includes an electrolyte salt and a solvent.

[0142] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0143] In some embodiments, the solvent may also be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane sulfone, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0144] In some embodiments, the electrolyte may further include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0145] [Isolation film]

[0146] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0147] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0148] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0149] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0150] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the secondary battery can be a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0151] In this application, the shape of the secondary battery includes but is not limited to cylindrical, square or any other shape. For example, FIG1 shows a secondary battery 5 with a square structure as an example.

[0152] In some embodiments, referring to FIG2 , the outer package may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the separator can be formed into an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0153] In some embodiments, secondary batteries can be assembled into a battery module. The number of secondary batteries contained in the battery module can be one or more. The specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0154] Figure 3 shows an example battery module 4. Referring to Figure 3 , within the battery module 4, multiple secondary batteries 5 may be arranged sequentially along the length of the battery module 4. Of course, any other arrangement is also possible. Furthermore, the multiple secondary batteries 5 may be secured together using fasteners.

[0155] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of secondary batteries 5 are accommodated in the accommodation space.

[0156] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0157] Figures 4 and 5 illustrate an example battery pack 1. Referring to Figures 4 and 5 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be placed over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0158] In addition, the present application also provides an electric device, which includes at least one of the secondary battery, battery module, or battery pack provided in the present application. The secondary battery, battery module, or battery pack can be used as a power source for the electric device, and can also be used as an energy storage unit for the electric device. The electric device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited thereto.

[0159] As an electrical device, a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

[0160] Figure 6 shows an example of an electric device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery, a battery pack or battery module can be used.

[0161] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0162] Example

[0163] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0164] 1. Preparation method

[0165] Example 1:

[0166] 1) Preparation of positive electrode sheet

[0167] The positive electrode active material LiNi 0.6 Co 0.07 Mn 0.33O2, binder polyvinylidene fluoride, and conductive agent acetylene black are mixed in a weight ratio of 98:1:1 and dissolved in solvent N-methylpyrrolidone (NMP) to form a positive electrode slurry. The slurry is then coated on a current collector aluminum foil. After drying, it is cold pressed, trimmed, cut, and slit to form a positive electrode sheet for a lithium-ion battery. The Dv50 of the positive electrode active material is 3.5 μm, and the solid-phase lithium ion diffusion coefficient Dp of the positive electrode active material is 1.69×10 -3 μm 2 / s, and the characteristic time constant Tp of solid phase diffusion is 1.81×10 3 s, the film thickness of the positive electrode sheet is 50 μm, and the porosity of the film is 22%.

[0168] 2) Preparation of negative electrode sheet

[0169] The negative electrode active material graphite, conductive agent carbon black, thickener CMC, and binder styrene-butadiene rubber (SBR) were mixed in a weight ratio of 96:2:1:1 and dissolved in deionized water to form a negative electrode slurry. The negative electrode slurry was obtained under the action of a vacuum mixer. The slurry was then coated on a current collector copper foil, dried, and then cold pressed, trimmed, cut, and slit to form the negative electrode sheet of the lithium-ion battery. The Dv50 of the negative electrode active material was 15 μm, and the mass content of the amorphous carbon coated in the negative electrode active material was 4% based on the total mass of the negative electrode active material. The solid-phase lithium ion diffusion coefficient Dn was 1.59×10 -1 μm 2 / s, and the characteristic time constant Tn of solid phase diffusion is 3.54×10 2 s, the film thickness of the negative electrode sheet is 62μm, and the film porosity is 32%.

[0170] 3) Preparation of electrolyte

[0171] In an argon atmosphere glove box (H2O content <0.1ppm, O2 content <0.1ppm), the solvent was mixed in the following mass ratio: ethylene carbonate: dimethyl carbonate: methyl acetate (mass ratio of 3:4:3), lithium hexafluorophosphate LiPF6 was dissolved in the organic solvent, and stirred evenly to obtain an electrolyte with a lithium salt concentration of 1 mol / L. The electrolyte conductivity was 1.4S / m, and the liquid phase diffusion coefficient was 466μm 2 / s.

[0172] 4) Isolation film

[0173] A 9 μm polyethylene (PE) film was used as the separator.

[0174] 5) Battery Preparation

[0175] The positive electrode sheet, the separator, and the composite negative electrode sheet are stacked in order, with the separator placed between the positive and negative electrode sheets to isolate the positive and negative electrode sheets. The bare battery cell is wound, the tabs are welded, and the battery cell is placed in an aluminum shell. The electrolyte is then injected and sealed. After standing, cold pressing, formation, shaping, capacity testing and other processes, the lithium-ion secondary battery prepared in Example 1 is obtained.

[0176] The preparation methods of the batteries of Examples 2-5 are similar to those of Example 1, except that the solid-phase diffusion coefficients of the positive and negative electrode active materials are adjusted by adjusting the Dv50 values ​​of the positive and negative electrode active materials or adjusting the components of the positive and negative electrode active materials, as follows:

[0177] Example 2

[0178] The battery preparation method of Example 2 is basically the same as that of Example 1, except that the component of the positive electrode active material in Example 2 is LiNi 0.60 Co 0.12 Mn 0.28 O2, the volume distribution particle size Lp is 3 μm, and the solid phase lithium ion diffusion coefficient Dp is 9.38×10 -3 μm 2 / s. The negative electrode active material graphite is composed of graphite. Based on the total mass of the negative electrode active material, the mass content of the amorphous carbon coated in the negative electrode active material is 2%. The volume distribution particle size L of the negative electrode active material is 10 μm, and the solid phase lithium ion diffusion coefficient Dp is 3.03×10 -2 μm 2 / s.

[0179] Example 3

[0180] The battery preparation method of Example 3 is basically the same as that of Example 1, except that the positive electrode active material in Example 3 is lithium iron phosphate, the volume distribution particle size Lp is 1 μm, and the solid phase lithium ion diffusion coefficient Dp is 8.43×10 -5 μm 2 / s. The negative electrode active material graphite is composed of graphite. Based on the total mass of the negative electrode active material, the mass content of the amorphous carbon coated in the negative electrode active material is 1%. The volume distribution particle size L of the negative electrode active material is 15 μm, and the solid phase lithium ion diffusion coefficient Dp is 4.63×10 -3 μm 2 / s.

[0181] Example 4

[0182] The battery preparation methods of Example 4 and Example 3 are basically the same, except that the positive electrode active material components in Example 4 are the same as those in Example 1, and the solid phase lithium ion diffusion coefficient Dp is 1.69×10 -3 μm 2 / s.

[0183] Example 5

[0184] The battery preparation method of Example 5 is basically the same as that of Example 3, except that the positive electrode active material in Example 5 has the same components as those in Example 2, the volume distribution particle size L is 2.5 μm, and the solid phase lithium ion diffusion coefficient Dp is 9.38×10 -3 μm 2 / s; the composition of the negative electrode active material is the same as that in Example 3, and Dv50 is 20 μm.

[0185] The preparation method of the battery of Example 6 is similar to that of the battery of Example 1, except that the value of Tep / Tp is adjusted by adjusting the thickness and porosity of the positive electrode film.

[0186] The preparation method of the battery of Example 7 is similar to that of the battery of Example 1, except that the positive electrode uses the positive electrode active material of Example 5, and the Tep / Tp value is adjusted by adjusting the thickness and porosity of the positive electrode film.

[0187] The preparation method of the battery of Example 8 is similar to that of the battery of Example 1, except that the negative electrode uses the negative electrode active material of Example 3, and the Ten / Tn value is adjusted by adjusting the thickness and / or porosity of the negative electrode film.

[0188] The preparation method of the battery of Example 9 is similar to that of the battery of Example 1, except that the negative electrode uses the negative electrode active material of Example 3, and the Ten / Tn value is adjusted by adjusting the thickness and / or porosity of the negative electrode film.

[0189] The battery preparation method of Example 10 is basically the same as that of Example 1, except that the component of the positive electrode active material in Example 11 is LiNi 0.6 Co 0.20 Mn 0.20 O2, the volume distribution particle size Lp is 2.4 μm, and the solid phase lithium ion diffusion coefficient Dp is 3.2×10 -2 μm 2 / s, the solid phase diffusion characteristic time constant Tp is 4.5×10s, the film thickness of the positive electrode is 120μm, and the film porosity is 15%.

[0190] The Dv50 of the negative electrode active material is 8 μm. Based on the total mass of the negative electrode active material, the mass content of the amorphous carbon coated in the negative electrode active material is 6%; the solid phase lithium ion diffusion coefficient Dn is 1.98 μm 2 / s, the solid phase diffusion characteristic time constant Tn is 8.08s, the film thickness of the negative electrode is 77μm, and the film porosity is 20%.

[0191] In an argon atmosphere glove box (H2O content <0.1ppm, O2 content <0.1ppm), the solvent was mixed in the following mass ratio: ethylene carbonate: diethyl carbonate (mass ratio of 3:7), lithium hexafluorophosphate LiPF6 was dissolved in the organic solvent, and stirred evenly to obtain an electrolyte with a lithium salt concentration of 1 mol / L. The electrolyte conductivity was 0.8S / m, and the liquid phase diffusion coefficient was 266μm 2 / s.

[0192] Example 11

[0193] The battery preparation method of Example 11 is basically the same as that of Example 10, except that the electrolyte ratio in Example 10 is as follows: the mass ratio of ethylene carbonate: diethyl carbonate: dimethyl carbonate is 3:2:5; the conductivity of the electrolyte is 1 S / m, and the liquid phase diffusion coefficient is 333 μm 2 / s.

[0194] Comparative Example 1

[0195] The battery preparation method in Comparative Example 1 is basically the same as that in Example 5, except that the Dv50 of the positive electrode active material is 2.5 μm; the Dv50 of the negative electrode active material is 20 μm.

[0196] Comparative Example 2

[0197] The battery of Comparative Example 2 was prepared in a similar manner to the battery of Example 3, except that the negative electrode active material was the same as that of Example 1, and Dv50 was 15 μm.

[0198] 2. Test Method

[0199] Battery performance test:

[0200] 1. Rate performance test

[0201] At 25°C, the prepared battery was fully discharged to 2.5V at a constant current of 0.33C. After standing for 30 minutes, it was charged to 4.25V at a constant current of 0.33C. The charging capacity at this time was recorded as C1. After standing for 30 minutes, it was discharged to 2.5V at a constant current of 0.33C. After standing for 30 minutes, it was charged to 4.25V at a constant current of 4C. The charging capacity at this time was recorded as C2. C2 / C1 is the 4C rate performance.

[0202] 2. Fast charge cycle life test and lithium plating test

[0203] 1) First, test the fast charging capability: charge and discharge the battery cell for the first time at a current of 1C (i.e., the current value that completely discharges the theoretical capacity within 1 hour). Specifically, at 35°C, charge the battery cell at a constant current rate of 1C to a voltage of 4.4V, then charge it at a constant voltage to a current of ≤0.05C, let it stand for 5 minutes, and then discharge it at a constant current rate of 0.33C to a voltage of 2.8V. Record its actual capacity as C0.

[0204] Then the battery cell is charged with a constant current of 1.0C0, 1.3C0, 1.5C0, 1.8C0, 2.0C0, 2.3C0, 2.5C0, 3.0C0, 3.5C0, 4C0, 4.5C0, and 5C0 in sequence to the full cell charge cut-off voltage of 4.4V or the negative electrode cut-off potential of 0V (whichever is reached first). After each charge is completed, it is necessary to discharge with 1C0 to the full cell discharge cut-off voltage of 2.8V. Record the state of charge (SOC) at different charge rates to 10%, 20%, 30%, ..., 80%. Charge, state of charge, when "SOC = 0" means the battery cell is fully discharged, when "SOC = 100%" means the battery cell is fully charged) the corresponding negative electrode potential, draw the charge rate-negative electrode potential curve under different SOC states, and after linear fitting, obtain the charge rate corresponding to the negative electrode potential of 0V under different SOC states. The charge rate is the charging window under the SOC state, which is recorded as "C10% SOC", "C20% SOC", "C30% SOC", "C40% SOC", "C50% SOC", "C60% SOC", "C70% SOC", and "C80% SOC" respectively.

[0205] 2) Fast charge cycle life

[0206] Perform step-by-step charging at the charging rate at each SOC obtained from the fast charging capability test. After charging to 10% SOC at the charging rate of "C10% SOC", charge to 20% SOC at the charging rate of "C20% SOC", continue to charge to 30% SOC at the charging rate of "C30% SOC", charge to 40% SOC at the charging rate of "C40% SOC", charge to 50% SOC at the charging rate of "C50% SOC", and finally charge to 60% SOC at the charging rate of "C60% SOC". ; Then charge to 70% SOC at the charging rate of "C70% SOC", then charge to 80% SOC at the charging rate of "C80% SOC", then charge to 100% SOC at 0.33C, and then discharge to 2.5V at a constant current of 0.33C. Record the discharge capacity at this time as the discharge capacity of the first cycle. After 100 cycles according to the above process, the discharge capacity of the 100th cycle is obtained. The capacity retention rate of the 100th cycle = the discharge capacity of the 100th cycle / the discharge capacity of the first cycle. Record the capacity retention rate of the 100th cycle as the fast charge cycle life.

[0207] Disassemble the battery and observe the lithium deposition on the negative electrode surface. If the lithium deposition area on the negative electrode surface is less than 5%, it is considered mild lithium deposition. If the lithium deposition area on the negative electrode surface is 5%-40%, it is considered moderate lithium deposition. If the lithium deposition area on the negative electrode surface is greater than 40%, it is considered severe lithium deposition.

[0208] 3. Analysis of test results of various embodiments and comparative examples

[0209] Batteries of various examples and comparative examples were prepared according to the above methods, and various performance parameters were measured. The results are shown in the table below.

[0210] Table 1

[0211] Table 2

[0212] As shown in Tables 1 and 2, 0.01≤Tp / Tn≤6 can effectively improve the rate performance of the battery. When 0.1≤Tp / Tn≤5.5, the rate performance of the battery is further improved.

[0213] Table 3

[0214] As can be seen from Table 3, 0.01≤Tep / Tp≤50 can further effectively improve the battery rate performance, while reducing lithium plating in the secondary battery and improving the battery quality.

[0215] Table 4

[0216] As can be seen from Table 4, 0.001≤Ten / Tn≤60 can further effectively improve the battery rate performance, while reducing lithium plating in the secondary battery and improving the battery quality.

[0217] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A lithium-ion battery, characterized in that: The lithium-ion battery comprises a positive electrode sheet and a negative electrode sheet; wherein the positive electrode sheet comprises a positive electrode active material, and the lithium ion solid phase diffusion characteristic time constant of the positive electrode active material is Tp, The negative electrode plate includes a negative electrode active material, and the lithium ion solid phase diffusion characteristic time constant of the negative electrode active material is Tn. And Tp and Tn satisfy: 0.01≤Tp / Tn≤6, Among them, the characteristic time constant of lithium ion solid phase diffusion of active material is T = (L / 2) 2 / D, in seconds, where L is the volume distribution particle size Dv50 of the active material, in μm, and D is the lithium ion solid phase diffusion coefficient of the active material, in μm 2 / s.

2. The lithium-ion battery according to claim 1, wherein 0.1≤Tp / Tn≤5.

5.

3. The lithium-ion battery according to claim 1 or 2, characterized in that 1×10s≤Tp≤5×10 3 s, in seconds; and / or, 2s≤Tn≤3×10 4 s, the unit is seconds.

4. The lithium-ion battery according to any one of claims 1 to 3, characterized in that The lithium ion solid phase diffusion coefficient of the positive electrode active material is Dp, the lithium ion solid phase diffusion coefficient of the negative electrode active material is Dn, and Dp and Dn satisfy: Dn>Dp.

5. The lithium-ion battery according to any one of claims 1 to 4, characterized in that The volume distribution particle size Dv50 of the positive electrode active material is Lp, the volume distribution particle size Dv50 of the negative electrode active material is Ln, and Lp and Ln satisfy: Ln>Lp.

6. The lithium-ion battery according to claim 5, characterized in that 5μm≤Ln≤20μm.

7. The lithium-ion battery according to claim 5, characterized in that 7μm≤Ln≤15μm.

8. The lithium-ion battery according to claim 5, characterized in that The positive electrode active material includes a lithium-containing phosphate material, and the volume distribution particle size Dv50 of the positive electrode active material satisfies: 0.3 μm≤Lp≤2 μm.

9. The lithium-ion battery according to claim 5, characterized in that The positive electrode active material includes a lithium-containing transition metal oxide, and the volume distribution particle size Dv50 of the positive electrode active material satisfies: 2 μm≤Lp≤10 μm.

10. The lithium-ion battery according to any one of claims 1 to 6, characterized in that The liquid phase diffusion characteristic time constant of the positive electrode plate is Tep, And Tep and Tp satisfy: 0.0001≤Tep / Tp≤60, which can be 0.01≤Tep / Tp≤50; The characteristic time constant of the liquid phase diffusion of the electrode is Where Le is the thickness of the film on one side of the current collector, in μm; De is the liquid phase diffusion coefficient at room temperature, in μm 2 / s; ε is the porosity of the membrane layer.

11. The lithium-ion battery according to claim 10, wherein: Tep satisfies: 3s≤Tep≤3×10 5 s, the unit is seconds.

12. The lithium-ion battery according to claim 10 or 11, characterized in that The liquid phase diffusion characteristic time constant of the negative electrode plate is Ten, Ten and Tn satisfy: 0.0004≤Ten / Tn≤70, and can be optionally 0.001≤Ten / Tn≤60.

13. The lithium-ion battery according to claim 12, wherein: Ten satisfies: 4s≤Ten≤2×10 5 s, the unit is seconds.

14. The lithium-ion battery according to any one of claims 10 to 13, characterized in that The conductivity of the electrolyte at room temperature is 0.6S / m-2S / m, and can be optionally 1.0S / m-1.8S / m.

15. The lithium-ion battery according to any one of claims 10 to 14, characterized in that The secondary battery includes an electrolyte, the electrolyte includes a linear carboxylate solvent, and the linear carboxylate solvent includes one or two of ethyl acetate, methyl acetate, methyl formate, butyl acetate, methyl propionate, ethyl propionate, methyl butyrate, propyl butyrate, butyl butyrate, isopropyl acetate, and isoamyl acetate.

16. The lithium-ion battery according to claim 15, characterized in that Based on the total mass of the electrolyte, the mass percentage of the linear carboxylate solvent is 5%-80%, and optionally 10%-70%.

17. The lithium-ion battery according to any one of claims 1 to 16, characterized in that The thickness of the positive electrode film layer on the current collector side is 32 μm-122 μm; and / or The porosity of the positive electrode film layer is 15%-50%.

18. The lithium-ion battery according to any one of claims 1 to 17, characterized in that The thickness of the negative electrode film layer on the current collector side is 29 μm-77 μm; and / or The porosity of the negative electrode film layer is 20%-60%.

19. An electrical device, characterized in that: A lithium ion battery comprising the lithium ion battery according to any one of claims 1 to 18.

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