Lithium ion battery and electric device

Abstract

The invention belongs to the technical field of batteries, and particularly relates to a lithium ion battery and an electric device. The lithium ion battery comprises a positive plate, a negative plate and an electrolyte, and meets the following conditions: 0.67 < = K = A / B < = 0.8; rho is smaller than or equal to-20.5 * (A + B) + 84.8, A is the compaction density of the positive plate, B is the compaction density of the negative plate, and rho is the viscosity of the electrolyte. According to the lithium ion battery, on the premise of ensuring high energy density, rapid and complete infiltration of the electrolyte is realized, the cycle life of the battery is remarkably prolonged, and the rate capability of the battery is remarkably improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of batteries, and particularly relates to a lithium ion battery and a power utilization device. BACKGROUND

[0002] With the rapid development of new energy vehicles and portable electronic devices, the market puts forward higher requirements for the energy density and cycle life of lithium ion batteries. Increasing the compaction density of electrode sheets is an effective means to improve the energy density, because it can fill more active materials in the same volume and directly increase the battery capacity. However, simply pursuing high compaction density will cause a series of problems: first, the electrolyte is difficult to infiltrate, and the over-dense electrode structure will hinder the infiltration and diffusion of the electrolyte, resulting in that the active material inside the electrode cannot be fully infiltrated, and the lithium ion migration impedance is significantly increased; second, the cycle performance is deteriorated, during the cycle process, the active material that is not fully infiltrated cannot participate in the electrochemical reaction and is disabled, and the local current density is too high, which will accelerate the destruction of the electrode structure and the growth of the solid electrolyte interface film, eventually causing the rapid decay of the battery capacity, the rapid increase of the internal resistance, and the significant shortening of the cycle life. Therefore, the related technology of lithium ion batteries still needs to be further improved. SUMMARY

[0003] The present application aims to at least solve one of the technical problems in the related art. To this end, the present application proposes a lithium ion battery and a power utilization device with higher cycle performance or rate performance.

[0004] In a first aspect of the present application, a lithium ion battery is provided, comprising a positive electrode sheet, a negative electrode sheet and an electrolyte, the lithium ion battery satisfies: 0.67≤K=B / A≤0.8; p≤-20.5×(A+B)+84.8; wherein A is the compaction density of the positive electrode sheet, unit g / cm 3 , B is the compaction density of the negative electrode sheet, unit g / cm 3 , and p is the viscosity of the electrolyte, unit mPa·s.

[0005] The present application systematically constructs a relatively optimal "electrode-electrolyte" system, thereby realizing the rapid and complete infiltration of the electrolyte under the premise of ensuring high energy density, and significantly improving the cycle life and rate performance of the battery.

[0006] According to the embodiments of the present application, the above lithium ion battery satisfies at least one of the following conditions: 0.7≤K≤0.75; p is 2.5 mPa·s ~ 4.5 mPa·s.

[0007] According to the embodiments of the present application, the above lithium ion battery satisfies at least one of the following conditions: The compaction density A of the positive electrode sheet is 2.2 g / cm 3 2.5 g / cm 3 ; The compaction density B of the negative electrode sheet is 1.4 g / cm 3 1.8 g / cm 3 , specifically 1.5 g / cm 3 1.8 g / cm 3 .

[0008] According to an embodiment of the present application, the positive electrode sheet comprises a positive electrode active material, the positive electrode active material comprises Li x Mn y Fe 1-y PO4, wherein 0.95≤x≤1.05, 0.05≤y≤0.95, the compaction density A of the positive electrode sheet decreases with the increase of the value of y in the positive electrode material, specifically A≤0.78y+1.96.

[0009] According to an embodiment of the present application, the positive electrode sheet further comprises a positive electrode current collector, and at least one of the following conditions is satisfied: The material of the positive electrode current collector comprises carbon-coated aluminum foil, light aluminum foil, PET composite aluminum foil; The thickness of the positive electrode current collector is 8 µm-20 µm.

[0010] According to an embodiment of the present application, the above lithium ion battery satisfies at least one of the following conditions: The area density SD1 of the positive electrode sheet is 150 g / m 2 250 g / m 2 ; The area density SD2 of the negative electrode sheet is 60 g / m 2 150 g / m 2 .

[0011] According to an embodiment of the present application, the negative electrode sheet comprises a negative electrode active material and a negative electrode current collector, and at least one of the following conditions is satisfied: The negative electrode active material of the negative electrode sheet comprises graphite, silicon-based material, titanium-based material; The material of the negative electrode current collector comprises copper foil; The thickness of the negative electrode current collector is 4 µm-20 µm.

[0012] According to an embodiment of the present application, the electrolyte comprises a solvent, an additive and an electrolyte salt, and at least one of the following conditions is satisfied: The solvent comprises at least one of dimethyl carbonate, ethylene carbonate, propylene carbonate, methyl ethyl carbonate, ethyl acetate, fluorobenzene; The additive includes at least one of cyclic carbonates, linear carboxylate, mixed solvents of sulfates and sulfites, phosphates / phosphites, borates, silanes / siloxanes, aromatic hydrocarbons; The electrolyte salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis-trifluoromethylsulfonylimide, lithium bis-oxalate-borate, lithium bis-fluoro-oxalate-borate, lithium bis-fluorosulfonylimide, lithium perchlorate.

[0013] According to the embodiment of the present application, the injection coefficient of the electrolyte is 2 g / Ah~4 g / Ah, specifically 2.5 g / Ah~3.5 g / Ah.

[0014] According to the embodiment of the present application, the NP ratio of the lithium ion battery is 1.05~1.25, specifically 1.10~1.15.

[0015] The second aspect of the present application proposes a power device, which includes the lithium ion battery of the first aspect. The power device includes all the features and advantages of the battery of the second aspect, which will not be described here. DETAILED DESCRIPTION

[0016] The embodiments of the present application are described in detail below, which are intended to explain the present application and cannot be understood as the limitation of the present application.

[0017] The first aspect of the present application proposes a lithium ion battery, which includes a positive electrode sheet, a negative electrode sheet and an electrolyte, and the lithium ion battery satisfies: 0.67≤K=B / A≤0.8; ρ≤-20.5×(A+B)+84.8; Wherein, A is the compaction density of the positive electrode sheet, unit g / cm 3 B is the compaction density of the negative electrode sheet, unit g / cm 3 ρ is the viscosity of the electrolyte, unit mPa·s.

[0018] The present application controls the ratio K of the compaction densities of the positive and negative electrodes and the viscosity p of the electrolyte in coordination, taking into account both high volumetric energy density and excellent cycle performance, and the specific advantages are as follows: on the one hand, by controlling the ratio K of the compaction densities of the positive and negative electrodes within a certain range, the positive electrode is kept in a relatively dense state, effectively improving the volumetric energy density of the battery; at the same time, the negative electrode is maintained in a relatively loose structure, providing sufficient space for electrolyte storage and building efficient channels for ion rapid migration, ensuring that the electrolyte rapidly and uniformly infiltrates the entire electrode system, and achieving synergistic improvement of energy density and cycle performance from the structural design level. On the other hand, by designing the relationship between the viscosity p of the electrolyte and the compaction densities of the positive and negative electrodes, an adaptation mechanism of electrolyte properties and electrode structure is established. When the compaction degree of the positive and negative electrodes is relatively high, the electrolyte with lower viscosity can quickly penetrate into the electrode, ensuring the ion transmission efficiency; when the compaction degree of the positive and negative electrodes is relatively low, the electrolyte with slightly higher viscosity and better electrochemical stability can be selected, which improves the cycle stability of the battery without affecting the infiltration effect. This matching relationship ensures that the electrolyte can achieve optimal infiltration and transmission effect under different compaction designs, further strengthening the reliability of the long cycle performance of the battery. In summary, the present application systematically constructs a relatively optimal "electrode-electrolyte" system, thereby realizing rapid and complete infiltration of the electrolyte under the premise of ensuring high energy density, and significantly improving the cycle life and rate performance of the battery.

[0019] According to embodiments of the present application, 0.7≤K≤0.75, specifically 0.7, 0.71, 0.72, 0.73, 0.74, 0.75 or any range between any two of them. Within the above range, the energy density and cycle performance of the lithium ion battery can be synergistically improved.

[0020] According to embodiments of the present application, p is 2.5 mPa·s ~4.5 mPa·s, specifically 2.5 mPa·s, 3 mPa·s, 3.5 mPa·s, 4 mPa·s, 4.5 mPa·s or any range between any two of them. Within the above range, the electrolyte can have both high conductivity and interface stability, and also provide excellent permeation fluidity.

[0021] The viscosity of the electrolyte refers to the measure of the difficulty of the electrolyte solution to flow. The interaction between positive and negative ions in the electrolyte solution and the interaction between solvent molecules and ions will affect the viscosity of the electrolyte. Generally, the test is carried out at 25°C by a rotary viscometer.

[0022] According to embodiments of the present application, the compaction density A of the positive electrode sheet is 2.2 g / cm 3 ~ 2.5 g / cm 3 , specifically 2.2 g / cm 3 , 2.3 g / cm3 2.4 g / cm 3 2.5 g / cm 3 or any range between any two of the above ranges. Within the above ranges, the battery can be guaranteed to have a high volumetric energy density and improved cycle performance.

[0023] According to an embodiment of the present application, the positive electrode sheet comprises a positive electrode active material layer comprising a positive electrode active material, the positive electrode active material comprising Li x Mn y Fe 1-y PO4 (LMFP), wherein 0.95≤x≤1.05, 0.05≤y≤0.95, the compaction density A of the positive electrode sheet decreases as the value of y in the positive electrode material increases, specifically A≤0.78y + 1.96. The above positive electrode active material has a high energy density, excellent structural stability and cycle life; the compaction density A of the positive electrode sheet satisfies the above condition, which can balance the energy density and electrolyte infiltration efficiency, and take into account high capacity and long cycle.

[0024] According to an embodiment of the present application, the areal density SD1 of the positive electrode sheet is 150 g / m 2 ~250 g / m 2 , specifically 150 g / m 2 , 170 g / m 2 , 190 g / m 2 , 210 g / m 2 , 230 g / m 2 , 250 g / m 2 or any range between any two of the above ranges. Within the above ranges, the mass of the positive electrode active material per unit area can be guaranteed, taking into account a high energy density and a moderate positive electrode sheet thickness.

[0025] According to an embodiment of the present application, the positive electrode sheet further comprises a positive electrode current collector, the material of the positive electrode current collector comprising a carbon-coated aluminum foil, an aluminum foil, a PET composite aluminum foil; the thickness of the positive electrode current collector is 8 μm ~ 20 μm. The above positive electrode current collector can provide support for the positive electrode active material, and at the same time has electrical conductivity, which can uniformly conduct electrons from an external circuit to the positive electrode active material, thereby significantly reducing the positive electrode interface impedance and ensuring the charging and discharging efficiency of the battery.

[0026] According to an embodiment of the present application, the positive electrode active material layer further comprises a positive electrode conductive agent, the positive electrode conductive agent comprising at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes (CNT), graphene.

[0027] According to embodiments of the present application, the positive active material layer further comprises a positive electrode binder, and the positive electrode binder comprises at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and a vinylidene-fluoride-tetrafluoroethylene-propylene terpolymer.

[0028] According to embodiments of the present application, the positive active material layer further comprises a positive electrode dispersant, and the positive electrode dispersant comprises, but is not limited to, polyvinylpyrrolidone (PVP), and the like.

[0029] According to embodiments of the present application, the negative sheet comprises a negative current collector, and a material of the negative current collector comprises a copper foil, including but not limited to a composite copper foil, a porous copper foil, and a copper foil commonly used in the art. The negative current collector can provide support for the negative active material, and has conductivity, so that electrons of an external circuit can be uniformly conducted to the negative active material, thereby significantly reducing the positive interface impedance and ensuring the battery charging and discharging efficiency.

[0030] According to embodiments of the present application, the thickness of the negative current collector is 4 mm-20 mm, specifically 4 mm, 6 mm, 8 mm, 10 mm, 12 mm, 14 mm, 16 mm, 18 mm, 20 mm, or a range between any two of them. Within the above range, the lithium ion battery has a higher energy density, so that it has a longer battery working time.

[0031] According to embodiments of the present application, the negative sheet further comprises a negative active material layer, and the negative active material layer comprises the negative active material. The negative active material comprises graphite, a silicon-based material, and a titanium-based material. Specifically, the silicon-based material comprises, but is not limited to, silicon-carbon material, and the titanium-based material comprises, but is not limited to, lithium titanate. The negative active material has high capacity and high energy density, and the preparation process is mature and the cost is low.

[0032] According to embodiments of the present application, the compaction density B of the negative sheet is 1.4 g / cm 3 ~ 1.8 g / cm 3 , specifically 1.5 g / cm 3 ~ 1.8 g / cm 3 . For example, the compaction density B of the negative sheet is specifically 1.4 g / cm 3 , 1.5 g / cm 3 , 1.55 g / cm 3 , 1.6 g / cm 3 , 1.65 g / cm 3 , 1.7 g / cm 3 , 1.75 g / cm 3 , 1.8 g / cm 3or a range between any two of them. Within the above range, the battery can be guaranteed to have a high volumetric energy density, and its cycle performance can be improved; meanwhile, the negative electrode sheet can maintain a relatively loose structure, providing sufficient space for electrolyte storage and building efficient channels for ion rapid migration, ensuring that the electrolyte rapidly and uniformly infiltrates the entire electrode system.

[0033] According to an embodiment of the present application, the surface density SD2 of the negative electrode sheet is 60 g / m 2 150 g / m 2 , specifically 60 g / m 2 , 70 g / m 2 , 80 g / m 2 , 90 g / m 2 , 100 g / m 2 , 110 g / m 2 , 120 g / m 2 , 130 g / m 2 , 140 g / m 2 , 150 g / m 2 , or a range between any two of them. Within the above range, the mass of the negative electrode active material per unit area can be guaranteed, and both a high energy density and a moderate negative electrode sheet thickness can be considered.

[0034] According to an embodiment of the present application, the negative electrode sheet further comprises a negative electrode binder, a negative electrode conductive agent, and a thickening agent.

[0035] According to an embodiment of the present application, the negative electrode binder comprises at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), and polyacrylamide (PAM).

[0036] According to an embodiment of the present application, the negative electrode conductive agent comprises at least one of superconducting carbon, acetylene black, carbon black, and graphene.

[0037] According to an embodiment of the present application, the thickening agent comprises sodium carboxymethyl cellulose (CMC-Na).

[0038] According to an embodiment of the present application, the electrolyte comprises a solvent, an additive, and an electrolyte salt. The above components synergistically act to guarantee ion transmission, interface stability, and cycle performance of the lithium ion battery.

[0039] According to an embodiment of the present application, the solvent comprises at least one of dimethyl carbonate, ethylene carbonate, propylene carbonate, methyl ethyl carbonate, ethyl acetate, and fluorobenzene. The above solvent helps to dissolve the electrolyte salt, so that the electrolyte has a relatively high ionic conductivity, which is conducive to long-term stable operation of the lithium ion battery.

[0040] According to the embodiment of the present application, the mass percentage of the solvent is 80% to 90% based on the total mass of the electrolyte, which is within the above range, is helpful to dissolve the electrolyte salt while reducing the viscosity of the system, and can make the electrolyte have a higher ionic conductivity after dissolving the electrolyte salt.

[0041] According to the embodiment of the present application, the additive includes at least one of cyclic carbonate, linear carboxylate, mixed solvent of sulfate and sulfite, phosphate / phosphite, borate, silane / siloxane, and aromatic hydrocarbon. The above additive is helpful to improve the cycle performance and rate performance of the lithium ion battery.

[0042] According to the embodiment of the present application, the cyclic carbonate includes fluoroethylene carbonate (FEC) and vinylene carbonate (VC).

[0043] According to the embodiment of the present application, the linear carboxylate includes methyl formate (MF), ethyl acetate (EA), methyl acetate (MA), methyl propionate (MP), and ethyl propionate (EP).

[0044] According to the embodiment of the present application, the mixed solvent of sulfate and sulfite includes vinyl sulfate (DTD), ethylene sulfite (ES), and propylene sulfite (PS).

[0045] According to the embodiment of the present application, the phosphate / phosphite includes tris(trimethylsilyl)phosphite (TMSP), trimethyl phosphite (TMP), and tris(2,2,2-trifluoroethyl)phosphite (TFEP).

[0046] According to the embodiment of the present application, the borate includes lithium bis(oxalato)borate (LiBOB), lithium bis(fluorooxalato)borate (LiFOB), tetramethyl borate (TMB), and tris(trimethylsilyl)borate (TMSB).

[0047] According to the embodiment of the present application, the silane / siloxane includes vinyltrimethoxysilane (VTMS), vinyltriethoxysilane (VTES), and hexamethyldisiloxane (HMDSO).

[0048] According to the embodiment of the present application, the aromatic hydrocarbon includes biphenyl (BP), fluoro-biphenyl (FBP), and fluorobenzene (FB).

[0049] According to the embodiment of the present application, the mass percentage of the additive is 2% to 10% based on the total mass of the electrolyte. Within the above range, it is helpful to improve the cycle performance and rate performance of the lithium ion battery.

[0050] According to embodiments of the present application, the electrolyte salt includes at least one of lithium hexafluorophosphate (LiFP6), lithium tetrafluoroborate (LiBF4), lithium bis-trifluoromethanesulfonylimide (LiTFSI), lithium bis(oxalato)borate (LiBOB), lithium bis(fluorosulfonyl)imide (LiFSI), lithium perchlorate (LiClO4). The above electrolyte salt has high ionic conductivity, low resistance and good chemical stability, so that the lithium ion battery using the electrolyte has the advantages of high energy density and long cycle life.

[0051] According to embodiments of the present application, the mass percentage of the electrolyte salt is 5% to 15% based on the total mass of the electrolyte. Within the above range, the electrolyte can have better conductivity and electrochemical stability.

[0052] According to embodiments of the present application, the injection coefficient of the electrolyte is 2 g / Ah to 4 g / Ah, specifically 2.5 g / Ah to 3.5 g / Ah. As an example, the injection coefficient of the electrolyte is 2 g / Ah, 2.5 g / Ah, 3 g / Ah, 3.5 g / Ah, 4 g / Ah or any range between any two of them. Within the above range, it can ensure that the electrolyte fills all the pores in the cell (including positive and negative electrode sheet pores, separator pores) and meets the liquid absorption demand of the active material surface, realizing uniform and deep infiltration of the electrode system.

[0053] The injection coefficient of the electrolyte refers to the ratio of the actual injected electrolyte mass (or volume) to the theoretically calculated required electrolyte mass (or volume) (the theoretical value is calculated based on the internal pore volume of the cell, the active material liquid absorption amount, etc.).

[0054] According to embodiments of the present application, the NP ratio of the lithium ion battery is 1.05 to 1.25, specifically 1.10 to 1.15. As an example, the NP ratio of the lithium ion battery can be 1.05, 1.10, 1.15, 1.20, 1.25 or any range between any two of them. Within the above range, the negative electrode reaction can be more uniform, reducing the interface side reaction, thereby reducing the impedance growth rate during the cycle process of the lithium ion battery and improving the capacity retention rate.

[0055] The N / P ratio refers to the ratio of the negative electrode capacity to the positive electrode capacity of the lithium ion battery, and the calculation formula is: N / P ratio = (negative electrode surface density x negative electrode material gram capacity) / (positive electrode surface density x positive electrode material gram capacity). Wherein, the "gram capacity" is the maximum capacity of the positive and negative active materials when completely deintercalating Li +

[0056] ​According to the embodiments of the present application, the lithium ion battery further comprises a separator, which can adopt various porous structure separators with good stability, such as polyethylene separator, polypropylene separator, PE ceramic coated separator, etc.

[0057] In the second aspect of the present application, a power consuming device is provided, which comprises the lithium ion battery of the first aspect. The power consuming device comprises all the features and advantages of the battery of the second aspect, which will not be repeated here.

[0058] It can be understood that the specific type of the power consuming device is not particularly limited, which can be any device using a battery as a power source or energy storage unit. As an example, the power consuming device includes but is not limited to 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.), mobile terminals (such as mobile phones, laptops, game consoles, wearable devices, etc.), drones, aerospace equipment, satellites, ships, energy storage systems, etc.

[0059] It can be understood that in addition to the above-mentioned battery, the power consuming device further comprises necessary structures and components, which can be referred to conventional technology, for example, an electric vehicle can comprise a vehicle body, a chassis, tires, a navigation system, a radar system, a steering system, a braking system, a lubrication system, a cooling system, a driving system, etc., which will not be repeated here.

[0060] The embodiments of the present application will be described in detail below.

[0061] Embodiment 1 (1) Preparation of the positive electrode sheet: the positive electrode active material LiMn 0.5 Fe 0.5 PO4, the positive electrode conductive agent acetylene black, the positive electrode binder PVDF and the positive electrode dispersant PVP are mixed in a mass ratio of 96:2:1.5:0.5, then added into N-methyl pyrrolidone solvent, stirred uniformly to obtain a positive electrode slurry with a solid content of 61%, and then the positive electrode slurry is uniformly coated on an aluminum foil, dried and rolled to obtain a positive electrode sheet; (2) Preparation of the negative electrode sheet: the graphite, the negative electrode conductive agent carbon black, carboxymethyl cellulose and butadiene rubber are mixed in a mass ratio of 8:1:0.5:0.5, then added into deionized water, mixed uniformly to obtain a negative electrode slurry with a solid content of 55%, and then the negative electrode slurry is uniformly coated on a copper foil, dried and rolled to obtain a negative electrode sheet; (3) Preparation of the electrolyte: the solvents are ethylene carbonate, propylene carbonate, methyl ethyl carbonate and dimethyl carbonate in a mass ratio of 30:5:25:40, the mass of the solvents accounts for 85% of the total mass of the electrolyte, the electrolyte salt is 1 mol / L lithium hexafluorophosphate, and the electrolyte additive is 2% VC; (4) Preparation of the separator: a commercially available 10 pm polyethylene separator was used; (5) Preparation of the battery: the positive electrode sheet, the negative electrode sheet and the separator were assembled in a laminated form, and then the electrolyte was injected, after formation and capacity distribution, the battery was obtained.

[0062] The specific parameters of Examples 2-16 and Comparative Examples 1-3 are shown in Table 1, and other parameters are the same as those of Example 1.

[0063] Performance test: (1) Compaction density: Compaction density = Area density / (thickness of the electrode sheet after compaction of the coating), first measure the thickness of the positive electrode sheet, use a laser thickness gauge to measure the total thickness T1 of the positive electrode sheet after compaction (unit: cm); then measure the thickness of the positive electrode current collector, use a laser thickness gauge to measure the thickness T2 of the current collector in the uncoated area of the positive electrode sheet; calculate the compaction density = area density / (T1-T2). The test method of the compaction density of the negative electrode sheet is the same as above.

[0064] (2) Area density: Area density = Coating mass / Coating area. Use a standard square cutter to cut a 10 cm x 10 cm square sample in the coating area of the positive electrode sheet; weigh the sample using a precision electronic balance (accuracy 0.1 mg), record as M1 (unit: mg); for the uncoated positive electrode current collector, take a 10 cm x 10 cm square sample, weigh it, record as M2; calculate the area density (mg / cm²) = (M1-M2) / 100. The test method of the area density of the negative electrode sheet is the same as above.

[0065] (3) K: K = B / A, where A is the compaction density of the positive electrode sheet, and B is the compaction density of the negative electrode sheet.

[0066] (4) NP ratio: the ratio of the negative electrode capacity to the positive electrode capacity, the calculation formula is N / P = (negative electrode area density x negative electrode material gram capacity) / (positive electrode area density x positive electrode material gram capacity).

[0067] (5) Viscosity p: at 25°C, slowly immerse the rotary viscometer into the electrolyte for testing, after the reading is stable, read the viscosity value.

[0068] (6) Energy density test Charge the battery at 25°C with 1 / 3C constant current, cut off at 4.2V, then charge at 4.2V constant voltage, cut off at 0.05C, rest for 0.5h, then discharge at 0.33C, cut off at 2.5V, get the discharge energy Q, energy density E = Q / V, where V represents the volume of the battery.

[0069] (7) Cycle test The battery was tested at 25℃ under 1C / 1C full charge and full discharge, with a cut-off voltage of 4.2V, and the capacity retention rate was recorded for 1000 cycles. The calculation formula of cycle retention rate: capacity retention rate = capacity after cycle / initial capacity x 100%.

[0070]

[0071] Conclusion: From the above examples, it can be seen that by accurately designing the ratio between the compaction densities of the positive and negative electrode sheets and matching the electrolyte of a specific viscosity, the electrolyte can be quickly and completely infiltrated under the premise of ensuring high energy density, significantly improving the performance of lithium ion batteries.

[0072] In the present application, the terms "first", "second" are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined with "first", "second" can explicitly or implicitly include at least one of the features. In the description of the present application, the meaning of "a plurality of" is at least two, for example, two, three, etc., unless otherwise specifically limited.

[0073] In the description of the present application, the description of the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In the present application, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. In addition, the skilled in the art can combine and combine the different embodiments or examples described in the present application and the features of the different embodiments or examples without contradiction.

[0074] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limiting the present application, and those skilled in the art can make changes, modifications, replacements and variations to the above embodiments within the scope of the present application.

Claims

1. A lithium-ion battery, characterized in that, The lithium-ion battery comprises a positive electrode, a negative electrode, and an electrolyte, and satisfies the following: 0.67 ≤ K = B / A ≤ 0.8; ρ≤-20.5×(A+B)+84.8; Where A is the compaction density of the positive electrode sheet, in g / cm³. 3 B is the compaction density of the negative electrode sheet, in g / cm³. 3 ρ is the viscosity of the electrolyte, in mPa·s.

2. The lithium-ion battery according to claim 1, characterized in that, At least one of the following conditions must be met: 0.7≤K≤0.75； ρ is 2.5 mPa·s ~ 4.5 mPa·s.

3. The lithium-ion battery according to claim 1, characterized in that, At least one of the following conditions must be met: The compaction density A of the positive electrode is 2.2 g / cm³. 3 ~ 2.5 g / cm 3 ; The compaction density B of the negative electrode is 1.4 g / cm³. 3 ~ 1.8 g / cm 3 1.5 g / cm 3 ~ 1.8 g / cm 3 .

4. The lithium-ion battery according to claim 1, characterized in that, The positive electrode sheet includes a positive electrode active material, which includes Li. x Mn y Fe 1-y PO4, wherein 0.95≤x≤1.05, 0.05≤y≤0.95, and the compaction density A of the positive electrode sheet decreases as the value of y in the positive electrode material increases, preferably A≤0.78y + 1.

96.

5. The lithium-ion battery according to claim 1, characterized in that, The positive electrode further includes a positive current collector, and satisfies at least one of the following conditions: The positive electrode current collector is made of materials including carbon-coated aluminum foil, plain aluminum foil, and PET composite aluminum foil; The thickness of the positive current collector is 8 μm to 20 μm.

6. The lithium-ion battery according to claim 1, characterized in that, At least one of the following conditions must be met: The areal density SD1 of the positive electrode is 150 g / m². 2 ~250 g / m 2 ; The areal density SD2 of the negative electrode is 60 g / m². 2 ~ 150 g / m 2 .

7. The lithium-ion battery according to claim 1, characterized in that, The negative electrode sheet includes a negative electrode active material and a negative electrode current collector, and satisfies at least one of the following conditions: The negative electrode active material of the negative electrode sheet includes graphite, silicon-based materials, and titanium-based materials; The negative electrode current collector is made of copper foil; The thickness of the negative electrode current collector is 4µm-20µm.

8. The lithium-ion battery according to claim 1, characterized in that, The electrolyte comprises a solvent, additives, and an electrolyte salt, and satisfies at least one of the following conditions: The solvent includes at least one of dimethyl carbonate, ethylene carbonate, propylene carbonate, ethyl methyl carbonate, ethyl acetate, and fluorobenzene. The additives include at least one of the following: cyclic carbonates, linear carboxylic acid esters, sulfate esters and sulfites, phosphate esters / phosphites, borate esters, silanes / siloxanes, and aromatic hydrocarbons; The electrolyte salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalateborate), lithium bis(fluorooxalateborate), lithium bis(fluorosulfonyl)imide, and lithium perchlorate.

9. The lithium-ion battery according to claim 1, characterized in that, The electrolyte injection coefficient is 2 g / Ah to 4 g / Ah, preferably 2.5 g / Ah to 3.5 g / Ah.

10. The lithium-ion battery according to claim 1, characterized in that, The lithium-ion battery has an NP ratio of 1.05 to 1.25, preferably 1.10 to 1.

15.

11. An electrical appliance, characterized in that, Including the lithium-ion battery according to any one of claims 1-10.

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