Lithium ion battery and electrical device

Abstract

A lithium ion battery and an electrical device. The lithium ion battery comprises: a positive electrode, a negative electrode, and an electrolyte (05), the negative electrode comprising a negative electrode current collector (03) and at least one negative electrode active material layer (04), and the negative electrode active material layer (04) being coated on one side or two sides of the negative electrode current collector (03). The total thickness of the negative electrode active material layer (04) on the single side of the negative electrode current collector (03) is d μm, the ionic conductivity of the electrolyte (05) is C mS / cm, and the viscosity of the electrolyte (05) is δ mPa•s, wherein the following relational expression is satisfied: 3≤d / (C*δ)≤6. Matching the electrolyte (05) with different ionic conductivity and viscosity can improve the wettability of the electrolyte (05) to electrode sheets effectively, thus improving the cycle performance of lithium ion batteries in a wide temperature range.

Description

Lithium-ion batteries and electrical equipment

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on March 28, 2024, with application number 202410377218.2 and application name “Lithium-ion Batteries and Electrical Equipment”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the technical field of lithium-ion batteries, and in particular to a lithium-ion battery and an electrical device. Background Art

[0003] Lithium-ion batteries are widely used in portable electronic devices, electric vehicles, smart grids, etc. due to their advantages such as high energy density, long cycle life, and no memory effect. In recent years, the requirements for the mass and / or volume energy density of lithium-ion batteries have been increasing year by year.

[0004] A common method to increase lithium-ion energy density is to load more active materials on electrodes of the same size. However, loading more active materials will increase the thickness and / or bulk density of the electrode, making it more difficult for the electrolyte to infiltrate and increase the transmission impedance of lithium ions in the electrode. Uneven infiltration will make the formed SEI film irregular, which will affect the battery's cycle performance over a wide temperature range during subsequent cycles.

[0005] Application Contents

[0006] In view of this, the present application provides a lithium-ion battery and electrical equipment, which can effectively improve the wetting of the electrolyte into the electrode by matching electrolytes with different ionic conductivities and viscosities, thereby improving the energy density of the lithium-ion battery while ensuring the wettability of the electrode and the transmission dynamics of lithium ions in the electrode, thereby improving the cycle performance of the lithium-ion battery in a wide temperature range.

[0007] In a first aspect, an embodiment of the present application provides a lithium-ion battery, the lithium-ion battery comprising:

[0008] A positive electrode comprising a positive electrode current collector and at least one positive electrode active material layer, wherein the positive electrode active material layer is coated on one side or both sides of the positive electrode current collector;

[0009] A negative electrode comprising a negative electrode current collector and at least one negative electrode active material layer, wherein the negative electrode active material layer is coated on one side or both sides of the negative electrode current collector, and the total thickness of the negative electrode active material layer on a single side of the negative electrode current collector is d μm;

[0010] The electrolyte has an ionic conductivity of C mS / cm and a viscosity of δ mPa·s.

[0011] Lithium-ion batteries satisfy the following relationship: 3≦d / (C*δ)≦6, where ionic conductivity C refers to the ionic conductivity at 25°C and viscosity δ refers to the shear rate of 50s at 25°C. -1 The corresponding viscosity.

[0012] In one embodiment, 6≦C≦12.

[0013] In one embodiment, 3≦δ≦5.

[0014] In one embodiment, 100≦d≦250.

[0015] In one embodiment, 70≦d'≦170.

[0016] In one embodiment, the vertical resistivity of the negative electrode sheet is R1Ω·cm, and the vertical resistivity of the positive electrode sheet is R2Ω·cm, satisfying the following relationship: 0.1≦R2 / R1≦0.5, 0.1≤d'*R2 / (d*R1)≤0.3.

[0017] In one embodiment, 5000≦R1≦6000.

[0018] In one embodiment, 1500≦R2≦2500.

[0019] In one embodiment, the electrolyte includes a solvent, and the solvent includes one or more of a cyclic carbonate, a linear carbonate, and a carboxylate compound;

[0020] The carboxylate compound comprises at least one of ethyl formate, methyl acetate, ethyl acetate, propyl acetate, ethyl propionate, propyl propionate, butyl propionate, pentyl propionate, ethyl haloacetate, ethyl halopropionate, propyl halopropionate, butyl halopropionate or pentyl halopropionate;

[0021] The linear carbonate comprises at least one of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, halogenated dimethyl carbonate, ethyl methyl carbonate, and halogenated diethyl carbonate;

[0022] The cyclic carbonate includes at least one of cyclic ethylene carbonate, cyclic propylene carbonate, halogenated cyclic ethylene carbonate, and halogenated cyclic propylene carbonate.

[0023] In one embodiment, the electrolyte further includes a lithium salt, and the lithium salt includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium trifluoromethanesulfonate, lithium perchlorate, lithium difluorooxalatoborate, and lithium dioxalatoborate.

[0024] In one embodiment, based on the total mass of the electrolyte, the lithium salt concentration is W%, and the following condition is met: 10≦W≦16.

[0025] In one embodiment, the negative electrode active material layer comprises a negative electrode active material, and the negative electrode active material comprises at least one of soft carbon, hard carbon, carbon fiber, graphitized carbon microbeads, artificial graphite, natural graphite, silicon, silicon carbide, and silicon-carbon composite materials.

[0026] In one embodiment, the positive electrode active material layer comprises a positive electrode active material, and the positive electrode active material comprises at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide.

[0027] In one embodiment, a lithium-ion battery includes a separator, which is disposed between a positive electrode and a negative electrode, and an electrolyte infiltrates the separator.

[0028] By matching electrolytes with different ionic conductivities and viscosities, the present application can effectively improve the wetting of the electrolyte into the electrode, reduce the transmission resistance of lithium ions in the electrode, and enable the high-energy-density lithium-ion battery to take into account the normal temperature cycle performance, high temperature cycle performance and low temperature discharge performance.

[0029] In a second aspect, embodiments of the present application further provide an electrical device, comprising the lithium-ion battery of the first aspect. The electrical device provided by embodiments of the present application, comprising the lithium-ion battery of the second aspect, exhibits excellent cycle performance over a wide temperature range, enabling the electrical device to be used stably for extended periods of time, thereby improving the performance of the electrical device under various operating conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] FIG1 is a schematic structural diagram of a lithium-ion battery according to a specific embodiment of the present invention;

[0031] In the figure, 01-positive electrode current collector, 02-positive electrode active material layer, 03-negative electrode current collector, 04-negative electrode active material layer, 05-electrolyte. DETAILED DESCRIPTION

[0032] The following is a clear and complete description of the technical solutions in the embodiments of this application. Obviously, the described embodiments are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which this application belongs. The terms used in this specification are for the purpose of describing specific embodiments only and are not intended to limit this application. The term "and / or" as used herein includes any and all combinations of one or more of the relevant listed items.

[0034] The following describes some embodiments of the present application in detail. In the absence of conflict, the following embodiments and features in the embodiments may be combined with each other.

[0035] Lithium-ion batteries, due to their high energy density, long cycle life, and lack of memory effect, are widely used in portable electronic devices, electric vehicles, and smart grids. Since the commercialization of lithium-ion batteries in 2000, the requirements for their mass and / or volumetric energy density have steadily increased. Besides using higher-capacity cathode or anode active materials to increase energy density, another simple and feasible approach is to increase the upper cutoff voltage for charging.

[0036] The above methods mainly improve energy density by improving materials. In addition, it is also a common method to increase energy density by loading more active materials on the same size of electrode through reasonable design. However, loading more active materials will increase the thickness and / or volume density of the electrode, which will make the electrolyte 05 infiltration more difficult and increase the transmission impedance of lithium ions in the electrode. Uneven infiltration will make the formed SEI irregular. In the subsequent cycle process, the solvent and / or additives continue to obtain electrons at the negative electrode interface and are reduced, resulting in gas production. The increase in the transmission impedance of lithium ions in the electrode leads to increased polarization of the battery cell during charging and discharging and a significant increase in the risk of lithium plating during the cycle, affecting the cycle performance of lithium-ion batteries under a wide temperature range.

[0037] Based on this, the present application provides a lithium-ion battery, which includes:

[0038] Positive electrode, the positive electrode includes a positive electrode collector 01 and at least one positive electrode active material layer 02, and the positive electrode active material layer 02 is coated on one side or both sides of the positive electrode collector 01; negative electrode, the negative electrode includes a negative electrode collector 03 and at least one negative electrode active material layer 04, and the negative electrode active material layer 04 is coated on one side or both sides of the negative electrode collector 03, and the total thickness of the negative electrode active material layer 04 on a single side of the negative electrode collector 03 is dμm; electrolyte 05, the ionic conductivity of the electrolyte 05 is C mS / cm, and the viscosity of the electrolyte 05 is δmPa·s. The lithium-ion battery satisfies the following relationship: 3≦d / (C*δ)≦6, wherein the ionic conductivity C refers to the ionic conductivity at 25°C, and the viscosity δ refers to the shear rate of 50s at 25°C. -1 The corresponding viscosity.

[0039] The value of d / (C*δ) indicates the relationship between the thickness of the negative electrode active material and the conductivity and viscosity of the electrolyte 05. When d / (C*δ)>6, the thickness of the corresponding lithium-ion battery negative electrode active material is too large, and the electrolyte 05 is difficult to fully infiltrate the pole piece, resulting in black spots in the infiltrated area during the normal temperature cycle of the battery, and then lithium precipitation, affecting the normal temperature cycle performance of the battery. When d / (C*δ)<3, the C*δ value of the corresponding lithium-ion battery electrolyte 05 is large. At this time, it contains more low-boiling point and low-viscosity solvents, and the oxidation resistance of the electrolyte 05 is poor, resulting in side reactions such as solvent oxidation that are prone to occur during the high-temperature cycle of the battery, which in turn causes the battery to swell and affect the high-temperature cycle performance. When 3≦d / (C*δ)≦6, the electrolyte 05 fully infiltrates the pole piece, and the oxidation resistance of the electrolyte 05 is good, so that the battery can have good cycle performance in a wide temperature range.

[0040] In one embodiment, the total thickness of the negative electrode active material layer 04 is d, which satisfies the following relationship: 100≦d≦250. Optionally, the negative electrode active material layer 04 can be a single layer, a double layer, or a multilayer. When the negative electrode active material layer 04 is a multilayer, the negative electrode active material layer 04 includes a first active material layer, a second active material layer, ..., an nth active material layer. The thickness of the first active material layer on a single side of the current collector is d1 μm, the thickness of the second active material layer is d2 μm, ..., and the thickness of the nth active material layer is d n μm, d1+d2+......+d n =d, satisfying 100≦d≦250. When the thickness of the negative electrode active material layer 04 is within this range, it ensures sufficient active material in the electrode, resulting in a high battery energy density, while also preventing excessive resistance to lithium ion transfer and thus battery performance degradation. Alternatively, the total thickness d of the negative electrode active material layer 04 can be 100, 102, 105, 110, 114, 120, 136, 143, 160, 188, 190, 200, 220, 250, or any value in between.

[0041] In one embodiment, the total thickness of the positive active material layer 02 on a single side of the positive current collector 01 is d'μm, satisfying the following condition: 70 ≤ d' ≤ 170. When the thickness of the positive active material layer 02 is within this range, it ensures a sufficient amount of active material in the electrode, resulting in a high battery energy density, while also minimizing the resistance to lithium ion transfer and preventing battery performance degradation. Alternatively, the total thickness d of the negative active material layer 04 can be 80, 85, 97, 100, 115, 124, 138, 150, 170, or any value in between.

[0042] In one embodiment, the vertical resistivity of the negative electrode sheet is R1Ω·cm, and the vertical resistivity of the positive electrode sheet is R2Ω·cm, satisfying the following relationship: 0.1≦R2 / R1≦0.5, 0.1≤d'*R2 / (d*R1)≤0.3. The vertical resistivity reflects the degree of obstruction of the electrode material to the current in the vertical direction. The resistivity of the positive / negative electrode is affected by many factors such as its material type, microstructure, doping conditions, particle size and distribution, porosity, and interface characteristics. When d', R1 and R2 meet the above relationship, the electronic conductance of the positive and negative electrodes is relatively balanced, and the lithium insertion / delithiation kinetics of the positive and negative electrodes are relatively matched, thereby avoiding increased polarization of the battery cell and increased risk of lithium plating at the negative electrode, thereby improving the energy density of the battery.

[0043] In one embodiment, the conductivity of the electrolyte 05 is C mS / cm, satisfying the following condition: 6≦C≦12. The magnitude of the conductivity depends on factors such as the ion concentration, ion mobility, and temperature of the electrolyte 05. Here, the ionic conductivity C refers to the ionic conductivity at 25°C. When the ionic conductivity of the electrolyte 05 is within this range, the ion concentration and mobility in the electrolyte 05 reach a balance point, making the electrolyte 05 neither too thin (low ion concentration) nor too viscous (ion migration is hindered), thereby promoting rapid ion conduction. Optionally, C is 6, 7, 7.5, 8, 9.6, 10.2, 11, 12, or any value in between these values.

[0044] In one embodiment, the viscosity of the electrolyte 05 is δmPa·s, which satisfies the following conditions: 3≦δ≦5, where the viscosity δ refers to the shear rate of 50s at 25°C. -1 The viscosity corresponding to the time. When the viscosity of electrolyte 05 falls within this range, electrolyte 05 typically contains a low content of low-boiling-point, low-viscosity solvents or a high content of lithium salts. This results in better oxidation resistance and makes side reactions such as solvent oxidation less likely to occur during high-temperature cycling. Furthermore, electrolyte 05 exhibits good fluidity, which facilitates electrolyte 05 wetting of the electrode and the transfer of lithium ions within the electrolyte 05, thereby improving the low-temperature discharge performance of the battery. Optionally, δ is 3, 3.4, 3.6, 4.0, 4.3, 4.8, 5.0, or any value in between.

[0045] In one embodiment, the vertical resistivity of the negative electrode is R1 Ω·cm, which satisfies the following condition: 5000 ≤ R1 ≤ 6000. When the vertical resistivity of the negative electrode is within this range, polarization of the battery during charge and discharge can be reduced, thereby improving the cycle life of the battery. Optionally, R1 is 5050, 5170, 5260, 5390, 5480, 5530, 5670, 5750, 5860, 5920, 6000, or any value in between.

[0046] In one embodiment, the vertical resistivity of the positive electrode is R2Ω·cm, which satisfies the following condition: 1500≦R2≦2500.

[0047] When the vertical resistivity of the positive electrode is within the above range, heat accumulation inside the battery can be avoided and the risk of thermal runaway can be reduced. Optionally, R2 is 1500, 1580, 1640, 1800, 1950, 2100, 2250, 2410, 2500 or any value in between.

[0048] In one embodiment, the electrolyte 05 includes a solvent, and the solvent includes one or more of a cyclic carbonate, a linear carbonate and a carboxylate compound; the carboxylate compound includes at least one of ethyl formate, methyl acetate, ethyl acetate, propyl acetate, ethyl propionate, propyl propionate, butyl propionate, pentyl propionate, ethyl haloacetate, ethyl halopropionate, propyl halopropionate, butyl halopropionate or pentyl halopropionate; the linear carbonate includes at least one of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, halogenated dimethyl carbonate, halogenated methyl ethyl carbonate and halogenated diethyl carbonate; the cyclic carbonate includes at least one of cyclic ethylene carbonate, cyclic propylene carbonate, halogenated cyclic ethylene carbonate and halogenated cyclic propylene carbonate. Cyclic carbonates have a high dielectric constant, which helps enhance the ionic conductivity of the electrolyte 05, thereby improving the battery's charge and discharge performance. Linear carbonates have a low viscosity and a high flash point, which helps improve the fluidity of the electrolyte 05, reduce internal resistance in the battery, and improve battery safety. Carboxylate compounds also have good chemical stability and wettability, and can form good interfacial contact with electrode materials, thereby improving battery performance. In summary, selecting one or more of cyclic carbonates, linear carbonates, and carboxylate compounds as the electrolyte 05 solvent, through reasonable combination and ratio, can comprehensively optimize battery performance.

[0049] In one embodiment, the electrolyte 05 further includes a lithium salt, which includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium trifluoromethanesulfonate, lithium perchlorate, lithium difluorooxalatoborate, and lithium dioxalatoborate. These lithium salts have high ionic conductivity and can effectively transfer lithium ions within the electrolyte 05, thereby improving the charge and discharge efficiency and performance of the battery. Furthermore, these lithium salts generally have good chemical stability within the operating voltage range of the battery and are not susceptible to decomposition or adverse chemical reactions with other battery components, thereby helping to ensure the long life and safety of the battery.

[0050] In one embodiment, the lithium salt concentration is W% based on the total mass of the electrolyte 05, satisfying the following condition: 10 ≤ W ≤ 16. When the lithium salt concentration is within this range, the electrolyte 05 has good wettability with the electrode and separator, the carrier concentration used for charge transport in the electrolyte 05 is moderate, the resistance during lithium ion transport is low, and the electrolyte 05 has good oxidation resistance.

[0051] In one embodiment, the electrolyte 05 further includes additives, including one or more of fluoroethylene carbonate, vinylene carbonate, 1,3-propane sultone, 1,3,6-hexane trinitrile, glycerol trinitrile, 1,2-bis(cyanoethoxy)ethane, 1,4-dicyano-2-butene, fumaronitrile, succinonitrile, and adiponitrile. Some additives (such as fluoroethylene carbonate and vinylene carbonate) can form a stable solid electrolyte interface (SEI) film on the surface of the positive and negative electrodes of the battery. This film helps prevent further reaction between the electrolyte 05 and the electrode material, reduces interfacial resistance, improves the stability of the electrolyte 05, and improves lithium ion transmission. At the same time, additives such as 1,3,6-hexane trinitrile and glycerol trinitrile can adjust the physical properties of the electrolyte 05, such as viscosity and density, to better meet the working requirements of the battery.

[0052] In one embodiment, the negative electrode active material layer 04 comprises a negative electrode active material, which includes at least one of soft carbon, hard carbon, carbon fiber, graphitized carbon microspheres, artificial graphite, natural graphite, silicon, silicon carbide, and a silicon-carbon composite material. Materials such as silicon and silicon carbide have high theoretical capacities. Materials such as soft carbon, hard carbon, and graphitized carbon microspheres exhibit minimal structural changes after multiple charge and discharge cycles, maintaining high capacity and efficiency. These materials also exhibit good wettability with the electrolyte 05, facilitating rapid lithium ion transport between the electrode and the electrolyte 05.

[0053] In one embodiment, the positive electrode active material layer 02 comprises a positive electrode active material, which includes at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide. These materials exhibit excellent electrochemical properties during charge and discharge, including high lithium ion diffusion coefficients, low polarization resistance, and stable crystal structures, helping the battery achieve rapid charge and discharge, high rate performance, and long cycle life.

[0054] In one embodiment, the lithium-ion battery further includes a diaphragm, which is disposed between the positive electrode and the negative electrode, and the electrolyte 05 infiltrates the diaphragm. The diaphragm can prevent the positive and negative electrodes of the battery from contacting each other and causing a short circuit, and can also regulate the fluidity and uniformity of the electrolyte 05, thereby improving battery performance and life.

[0055] The present application also provides an electrical device comprising a lithium-ion battery according to any of the above embodiments. Specifically, the electrical device may be an electric car, an electric motorcycle, an electric bicycle, a power bank, an unmanned aerial vehicle, a mobile phone, a computer, a camera, a power tool, a smart home device, or a wearable device.

[0056] The electrical equipment provided in the embodiment of the present application includes a lithium-ion battery, which has a long cycle life and good rate performance in a wide temperature range, so that the electrical equipment can be used stably for a long time, which is beneficial to improving the performance of the electrical equipment.

[0057] The technical solution of the present application is further illustrated below through specific examples and comparative examples.

[0058] Example 1

[0059] (1) Preparation of electrolyte 05

[0060] In an argon atmosphere glove box with a water content of <1ppm and an oxygen content of <1ppm, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), propyl propionate (PP), and ethyl propionate (EP) solvents were uniformly mixed in a certain mass ratio, and then fluoroethylene carbonate (FEC), 1,3-propane sultone (PS), 1,3,6-hexanetrionitrile, and adiponitrile (ADN) were added to the solvent in a certain mass ratio and uniformly mixed, and finally LiPF6 was added.

[0061] (2) Preparation of positive electrode sheet

[0062] The positive electrode active material, lithium cobalt oxide (LiCoO2), the conductive agent, carbon nanotubes (CNT), and the specific binder, polyvinylidene fluoride, were mixed in a mass ratio of 95:2:3. N-methylpyrrolidone (NMP) was added and stirred in a vacuum mixer until the system formed a uniform positive electrode slurry. The positive electrode slurry was then evenly coated on the positive electrode current collector, 0.1Al foil. After drying at 85°C, the product was cold pressed, slit, and cut into pieces, and then dried under vacuum conditions at 85°C for 4 hours to obtain the positive electrode sheet.

[0063] (3) Negative electrode preparation

[0064] The negative electrode active material graphite, the binder styrene-butadiene rubber (SBR), and the thickener sodium carboxymethyl cellulose (CMC) were thoroughly mixed in a suitable amount of deionized water at a mass ratio of 95:2:3 to form a uniform negative electrode slurry. This slurry was applied to the negative electrode current collector (Cu foil) to form the first negative electrode active material layer (4). The negative electrode active material graphite, the binder styrene-butadiene rubber (SBR), and the thickener sodium carboxymethyl cellulose (CMC) were thoroughly mixed in a suitable amount of deionized water at a mass ratio of 96:1.5:2.5 to form a uniform negative electrode slurry. This was applied to the first negative electrode active material layer (4) to form the second negative electrode active material layer (4). After drying, cold pressing, slitting, and cutting, the negative electrode sheet was obtained.

[0065] (4) Diaphragm preparation

[0066] The diaphragm is made of polypropylene.

[0067] (5) Preparation of lithium-ion batteries

[0068] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator placed between the positive and negative electrode sheets to act as an isolate. Then they are wound and placed in outer packaging foil. The prepared electrolyte 05 is injected into the dried battery. After vacuum packaging, standing, formation, shaping and other processes, the preparation of the lithium-ion battery is completed.

[0069] Examples 2 to 13

[0070] By adjusting the ratio of solvent, additive and lithium salt in electrolyte 05 and the thickness of the active material layer of the positive and negative electrodes, the ionic conductivity and viscosity of electrolyte 05, the thickness and vertical conductivity of the active material layer of the positive and negative electrodes are shown in Table 1. The remaining steps are the same as those in Example 1.

[0071] Comparative Examples 1 to 4

[0072] By adjusting the ratio of solvent, additive and lithium salt in electrolyte 05 and the thickness of the active material layer of the positive and negative electrodes, the ionic conductivity and viscosity of electrolyte 05, the thickness and vertical conductivity of the active material layer of the positive and negative electrodes are shown in Table 1. The remaining steps are the same as those in Example 1.

[0073] Table 1 Physical parameters of the electrode and electrolyte 05 of the embodiment and comparative example

[0074] Test method:

[0075] (1) Viscosity test

[0076] Anton Paar MCR92 rheometer was used at a constant temperature of 25°C and a shear rate of 0.1 to 300 s -1Shearing was performed to obtain the viscosity curve at different shear rates, and the shear rate was read as 50±3s -1 The viscosity at 5°C is taken as the viscosity of electrolyte 05.

[0077] (2) High temperature cycle test

[0078] Take the prepared lithium-ion battery and charge it to 4.45V at a constant current of 1C rate at high temperature (45±3℃), then charge it to 0.05C at a constant voltage at 4.45V, let it sit for 5 minutes, and then discharge it to 3.0V at a constant current of 1C rate, let it sit for 5 minutes. This is one cycle. Record the capacity retention rate and thickness expansion rate (1000 full-charge thickness / first full-charge thickness) after 1000 high-temperature cycles. The cycle uses a NEWARE test cabinet (model CTE-4080D-5V30A). In order to ensure that the battery temperature is constant during the cycle test, the battery is placed in a high and low temperature test chamber (model CH1000T). The battery thickness test uses a PPG tester (model ATMPPGSH200).

[0079] (3) 20 cycles at 0℃

[0080] After the prepared lithium-ion battery was placed at 0°C for 2 hours, it was charged to 4.45V at a constant current rate of 0.5C. It was then charged to a current of 0.05C at 4.45V and allowed to stand for 5 minutes. It was then discharged to 3.0V at a constant current rate of 0.5C and allowed to stand for 5 minutes. This constituted one cycle. After 20 cycles, the battery was fully charged according to the above conditions and disassembled in an inert gas-protected glove box. The lithium deposition on the surface of the negative electrode was recorded. If there was obvious silvery-white metallic product deposited on the large surface of the negative electrode, the tabs, or the folds, it was considered lithium deposition. In severe cases, the lithium metal will react with the electrolyte 05, causing the lithium metal to gradually change from silvery-white to yellow-brown and eventually to black.

[0081] (4) -20℃ discharge test

[0082] Take the prepared lithium-ion battery and charge it to 4.45V at a constant current rate of 0.2C at room temperature (25±3℃), then charge it to a current of 0.05C at a constant voltage at 4.45V, let it sit for 5 minutes, and then discharge it to 3.0V at a constant current rate of 0.2C, let it sit for 5 minutes. Record the 0.2C discharge capacity at room temperature as the initial capacity of the battery. Then charge the lithium-ion battery to 4.45V at a constant current rate of 0.2C, then charge it to a current of 0.05C at 4.45V, let it sit for 5 minutes, and then place the lithium-ion battery at -20℃ and let it sit for 2 hours, then discharge it to 3.0V at a constant current rate of 0.2C. Record the 0.2C discharge capacity at -20℃. (Discharge retention rate at -20℃ = 0.2C discharge capacity at -20℃ / initial capacity of battery

[0083] *100%)

[0084] (5) Ionic conductivity test

[0085] Ionic conductivity is tested using a conductivity meter (Model: S230) and a constant temperature water bath (Model: CBC5CS025). Before each test, calibration is performed using a standard solution with an ionic conductivity of 12.88 mS / cm. After calibration, the electrodes are cleaned and then directly inserted into the electrolyte solution (0.5%) for testing. The results are read and recorded directly on the conductivity meter. The constant temperature water bath controls the temperature of the electrolyte solution (0.5%) and is typically maintained at room temperature (25°C).

[0086] (6) Vertical resistivity test

[0087] The vertical resistivity test is carried out using a pole piece resistance meter (model: IEST BSR2500). A pole piece sample of a certain size is placed on the cutting table and placed in the test cavity of the resistance meter. The resistance reading in the instrument software is read. According to the resistance meter probe diameter, pole piece thickness, and resistivity calculation formula (ρ=R*S / L, R in Ω, S in cm) 2 , L is in cm) calculate the vertical resistivity of the electrode to be tested.

[0088] Table 2 Cyclic test and lithium deposition test results

[0089] From the results in Table 1 and Table 2, it can be seen from the comparison of Examples 1-13 and Comparative Examples 1-4 that when the value of d / (C*δ) is greater than 6, the lithium-ion battery undergoes significant lithium plating after low-temperature cycling, and the low-temperature discharge retention rate is low. This is because the negative electrode active material layer is relatively thick, the electrolyte 05 is insufficient to completely infiltrate the negative electrode sheet, the battery impedance increases, and thus lithium plating occurs at the negative electrode. When the value of d / (C*δ) is less than 3, a high proportion of low-viscosity solvents are present in the electrolyte 05, so the low-temperature discharge and low-temperature cycling performance will be improved. However, since low-viscosity solvents generally have a low boiling point and poor oxidative stability, the electrolyte 05 will oxidize during high-temperature cycling, resulting in gas production inside the battery cell, a larger thickness expansion rate, and a significant decrease in capacity retention. When 0.1≤d'*R2 / (d*R1)≤0.3 is further satisfied, the negative electrode lithium insertion kinetics and the positive electrode lithium removal kinetics remain relatively balanced during charging, improving negative electrode lithium plating and increasing the low-temperature discharge rate at -20°C.

[0090] The above are preferred embodiments of the present application, but they should not be construed as limiting the scope of the present application. It should be noted that those skilled in the art may make improvements and modifications without departing from the principles of the present application, and such improvements and modifications are also considered to be within the scope of protection of the present application.

Claims

1. A lithium-ion battery, characterized in that: The lithium-ion battery comprises: A positive electrode, the positive electrode comprising a positive electrode current collector (01) and at least one positive electrode active material layer (02), wherein the positive electrode active material layer (02) is coated on one side or both sides of the positive electrode current collector (01); A negative electrode, the negative electrode comprising a negative electrode current collector (03) and at least one negative electrode active material layer (04), the negative electrode active material layer (04) being coated on one side or both sides of the negative electrode current collector (03), and the total thickness of the negative electrode active material layer (04) on one side of the negative electrode current collector (03) being d μm; An electrolyte (05), wherein the ionic conductivity of the electrolyte (05) is C mS / cm, the viscosity of the electrolyte (05) is δ mPa·s, The lithium ion battery satisfies the following relationship: 3≦d / (C*δ)≦6, wherein the ionic conductivity C refers to the ionic conductivity at 25°C, and the viscosity δ refers to the shear rate of 50s at 25°C. -1 The corresponding viscosity.

2. The lithium-ion battery according to claim 1, wherein 6≦C≦12。 3. The lithium-ion battery according to claim 1, wherein 3≦δ≦5.

4. The lithium-ion battery according to claim 1, wherein 100≦d≦250。 5. The lithium-ion battery according to claim 1, wherein The total thickness of the positive electrode active material layer (02) on one side of the positive electrode current collector (01) is d'μm, which satisfies the following condition: 70≦d'≦170.

6. The lithium-ion battery according to claim 1, wherein The vertical resistivity of the negative electrode is R1Ω·cm, and the vertical resistivity of the positive electrode is R2Ω·cm, satisfying the following relationship: 0.1≦R2 / R1≦0.5, 0.1≦d'*R2 / (d*R1)≦0.

3.

7. The lithium-ion battery according to claim 6, characterized in that 5000≦R1≦6000。 8. The lithium-ion battery according to claim 6, wherein 1500≦R2≦2500。 9. The lithium-ion battery according to any one of claims 1 to 8, characterized in that: The electrolyte (05) includes a solvent, and the solvent includes one or more of cyclic carbonate, linear carbonate and carboxylic acid ester compounds; The carboxylate compound comprises at least one of ethyl formate, methyl acetate, ethyl acetate, propyl acetate, ethyl propionate, propyl propionate, butyl propionate, pentyl propionate, ethyl haloacetate, ethyl halopropionate, propyl halopropionate, butyl halopropionate or pentyl halopropionate; The linear carbonate comprises at least one of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, halogenated dimethyl carbonate, halogenated ethyl methyl carbonate, and halogenated diethyl carbonate; The cyclic carbonate includes at least one of cyclic ethylene carbonate, cyclic propylene carbonate, halogenated cyclic ethylene carbonate, and halogenated cyclic propylene carbonate.

10. The lithium-ion battery according to claim 9, characterized in that The electrolyte (05) further comprises a lithium salt, wherein the lithium salt comprises one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium trifluoromethanesulfonate, lithium perchlorate, lithium difluorooxalatoborate, and lithium dioxalatoborate.

11. The lithium-ion battery according to claim 10, wherein: Based on the total mass of the electrolyte (05), the lithium salt concentration is W%, satisfying the following condition: 10≦W≦16.

12. The lithium-ion battery according to claim 9, characterized in that The electrolyte (05) also includes additives, which include one or more of fluoroethylene carbonate, vinylene carbonate, 1,3-propane sultone, 1,3,6-hexane trinitrile, glycerol trinitrile, 1,2-bis(cyanoethoxy)ethane, 1,4-dicyano-2-butene, fumaronitrile, succinonitrile, and adiponitrile.

13. The lithium-ion battery according to any one of claims 1 to 12, characterized in that: The negative electrode active material layer (04) contains a negative electrode active material, and the negative electrode active material contains at least one of soft carbon, hard carbon, carbon fiber, graphitized carbon microspheres, artificial graphite, natural graphite, silicon, silicon carbide, and silicon-carbon composite materials.

14. The lithium-ion battery according to any one of claims 1 to 12, characterized in that: The positive electrode active material layer (02) contains a positive electrode active material, and the positive electrode active material contains at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide.

15. The lithium-ion battery according to any one of claims 1 to 12, characterized in that: It also includes a diaphragm, which is arranged between the positive electrode and the negative electrode, and the electrolyte (05) infiltrates the diaphragm.

16. An electrical device, characterized in that: A lithium-ion battery comprising the lithium-ion battery according to any one of claims 1 to 15.

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