Battery

Abstract

The invention relates to the technical field of batteries, in particular to a battery. Comprising a positive plate and electrolyte, the positive plate comprises a positive current collector and a coating positioned on the surface edge of at least one side of the positive current collector along the length direction; the coating comprises filling particles, and the filling particles comprise at least one of inorganic particles and nitrogen-containing particles; the electrolyte comprises non-fluorinated cyclic carbonate and fluorinated ethyl acetate; the non-fluorinated cyclic carbonate comprises propylene carbonate and optional ethylene carbonate; on the basis of the total mass of the electrolyte, the content ratio C1 of the non-fluorinated cyclic carbonate is smaller than or equal to 25%, the content ratio C11 of the propylene carbonate is 3.1%-24.9%, the content ratio C12 of the ethylene carbonate is 0%-5%, and the content ratio C2 of the fluorinated ethyl acetate is 20.2%-70%. The battery provided by the invention can improve the problem of lithium precipitation under low-temperature discharge, and has relatively good short-circuit safety performance and relatively low high-temperature gas production rate.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a battery. BACKGROUND

[0002] With the current vigorous development of lithium ion batteries, there are many application scenarios, such as electric vehicles, electric motorcycles, unmanned aerial vehicles, and the requirements for lithium ion batteries are gradually extreme. Coating a safety coating on the edge of the positive plate can inhibit the short circuit caused by the burr of the active material layer on the edge of the positive plate piercing the separator, thereby improving the safety performance of the battery. However, it is found in actual use that under the condition of low-temperature discharge of the battery, purple lithium precipitation occurs on the edge and middle part of the negative plate, especially in the edge area.

[0003] Therefore, it is very important to invent a battery with short-circuit safety performance and improved lithium precipitation problem on the edge and middle part of the negative plate during low-temperature discharge. SUMMARY

[0004] The purpose of the present application is to overcome the problem of lithium precipitation on the edge and middle part of the negative plate during low-temperature discharge of the battery caused by setting a safety coating on the edge of the positive plate in the prior art, and to provide a battery. The battery of the present application has good short-circuit safety performance by cooperating with the positive plate and the electrolyte, significantly improves the problem of lithium precipitation on the edge and middle part of the negative plate during low-temperature discharge, and has less gas production under high-temperature conditions, further improving the safety performance of the battery.

[0005] In the related art, setting a safety coating on the edge of the positive plate can cause the problem of lithium precipitation on the edge and middle part of the negative plate during low-temperature discharge of the battery, especially in the edge area. The lithium precipitation phenomenon in the lithium ion battery refers to the phenomenon that during charging or low-temperature discharge, lithium ions cannot be normally embedded in the crystal lattice of the negative electrode material (such as graphite), but are deposited in the form of metallic lithium on the surface of the negative electrode. The inventors of the present application have found through a large number of studies that the cause of the above problem is that in a low-temperature environment, the lithium intercalation overpotential of the negative electrode increases significantly, and the risk of lithium precipitation increases sharply. In particular, after setting a safety coating on the edge of the positive plate, due to the edge effect, the current distribution is uneven, the local current density in the edge area is higher, and more lithium ions need to be accepted, further exacerbating the tendency of lithium precipitation; and the special structure of the edge area increases the interfacial impedance, and this polarization effect is more obvious at low temperature, making the local potential of the negative electrode more likely to drop below the lithium precipitation potential. The middle area causes lithium precipitation due to poor electrolyte wetting.

[0006] Based on the above reasons, the inventors of the present application have conducted a large amount of research and found that the problem of lithium precipitation at the edge and middle of the negative plate caused by the setting of the safety coating can be improved by starting with uniformizing the current distribution: through the optimization of the electrolyte composition, the wettability and charge transfer impedance of the electrode / electrolyte interface can be adjusted to make the current distribution more uniform. First, non-fluorinated cyclic carbonate can effectively dissociate lithium salt due to its high dielectric constant, providing sufficient free lithium ions. However, the coordination ability of non-fluorinated cyclic carbonate to lithium ions is strong, and if the content ratio is too high, it will cause the lithium ion solvation sheath to be too stable, increasing the desolvation energy barrier (especially under low temperature conditions), thereby delaying the desolvation process of lithium ions at the negative electrode interface, exacerbating polarization, and inducing lithium precipitation. Therefore, it is necessary to limit the total content ratio of non-fluorinated cyclic carbonate in the electrolyte. Second, under low temperature conditions, propylene carbonate (PC) has a lower melting point and viscosity than ethylene carbonate (EC), which can maintain good fluidity and improve the transport rate of lithium ions in the electrolyte. And because the antioxidant capacity of EC is limited, the mass content ratio of the two in the electrolyte needs to be adjusted. Third, fluoroethyl acetate has a low LUMO energy level and can be preferentially reduced on the negative electrode surface to form a SEI film rich in LiF. LiF has high interfacial energy and mechanical strength, which can effectively inhibit the growth of lithium dendrites; at the same time, the high ionic conductivity and low electronic conductivity of LiF ensure the uniform transmission of lithium ions and reduce the interfacial impedance. On the other hand, the addition of fluoroethyl acetate can lower the freezing point of the electrolyte and improve the ion conduction performance at low temperature. The specific components in the above electrolyte can not only ensure low viscosity and lithium salt solubility of the electrolyte, but also increase the conductivity of the electrolyte. It can also form a thin and dynamic SEI film near the surface of the negative plate corresponding to the positive plate coating, which can improve the lithium precipitation window of the battery while not deteriorating the high temperature performance of the battery.

[0007] In addition, it needs to be emphasized that the optimization of the above electrolyte also takes into account the composition of the coating, as follows: The surface of the brucite is rich in hydroxyl groups and Lewis acid sites Al 3+ The above hydroxyl groups can form a hydrogen bond network with the fluorine atoms in fluoroethyl acetate, reducing the interfacial energy; and the Lewis acid sites Al 3+ can coordinate with the fluorine atoms and carbonyl groups (-C=O-) in fluoroethyl acetate, further enhancing the interaction between fluoroethyl acetate. This interaction can induce the formation of an ordered lithium ion transport channel near the electrolyte interface, thereby reducing the lithium ion migration resistance and reducing the occurrence of lithium precipitation. The surface of aluminum oxide has a large number of Lewis acid sites Al 3+As mentioned above, the interaction with ethyl fluoroacetate can be enhanced, thereby reducing the occurrence of lithium precipitation. The nitrogen-containing group (e.g., -NH-) in the nitrogen-containing particle (e.g., melamine cyanurate) can form a hydrogen bond network with the carbonyl group or fluorine atom in ethyl fluoroacetate, and the nitrogen atom in the nitrogen-containing group can form a hydrogen bond network with the a-hydrogen (-CH2-) or -CF2H in the ester group of ethyl fluoroacetate, thereby reducing the interfacial energy and reducing the occurrence of lithium precipitation.

[0008] The inventors of the present application found that the above-mentioned combination not only improves the lithium precipitation problem of the negative electrode sheet during the low-temperature discharge process of the battery, but also enables the battery to have less gas production under high-temperature conditions, thereby improving the high-temperature safety performance of the battery. The reason is as follows: first, the Lewis acid sites Al 3+ on the surface of brucite and alumina can chemically adsorb HF generated by the decomposition of the electrolyte, thereby preventing the HF from corroding the positive / negative interfacial film. Moreover, ethyl fluoroacetate preferentially decomposes to generate LiF and fluorine-containing organic matter under high temperature, which can form a composite interfacial film with brucite or alumina that has higher thermal stability, thereby reducing the occurrence of gas production. Second, the nitrogen-containing group (e.g., -NH-, -NH2, etc.) in the nitrogen-containing particle can capture free radicals generated by the decomposition of the electrolyte under high temperature, interrupt the chain reaction, and inhibit the oxidative gas production of the carbonate solvent. In addition, the electron-rich nitrogen-containing group can temporarily store the oxidation holes released by the positive electrode, thereby delaying the oxidative decomposition of the electrolyte.

[0009] Based on this, the inventors of the present application propose the following solutions:

[0010] The present application provides a battery, comprising a positive electrode sheet and an electrolyte; the positive electrode sheet comprises a positive electrode current collector and a coating layer located on the surface edge of at least one side of the positive electrode current collector along the length direction; the coating layer comprises filler particles, and the filler particles comprise at least one of inorganic particles and nitrogen-containing particles; the inorganic particles comprise at least one of brucite, alumina, and magnesium oxide, and the nitrogen-containing particles comprise at least one of melamine, melamine cyanurate, melamine polyphosphate, melamine trithiocyanate, and melamine formaldehyde resin; the electrolyte comprises non-fluorinated cyclic carbonate and ethyl fluoroacetate; the non-fluorinated cyclic carbonate comprises propylene carbonate and optionally vinyl carbonate; based on the total mass of the electrolyte, the content ratio of the non-fluorinated cyclic carbonate is C1≤25%, the content ratio of propylene carbonate is C11 is 3.1%-24.9%, the content ratio of vinyl carbonate is C12 is 0%-5%, and the content ratio of the ethyl fluoroacetate is C2 is 20.2%-70%.

[0011] Compared with the prior art, the present application has at least the following advantages:

[0012] (1) The battery of the present application has higher short-circuit safety performance, and significantly improves the problem of lithium precipitation at the edge and middle of the negative electrode sheet during low-temperature discharge.

[0013] (2) The battery of the present application has lower high-temperature gas production.

[0014] The endpoints of the ranges and any values disclosed herein are not limited to the precise values recited as the exact dimensions are not critical to the present application. Any numerical value, however, can be expressed as a range to include any and all expressed values falling within the indicated ranges. The endpoints of the ranges and any values are provided as a separate value from but within the indicated range. All individual values and subranges from the stated ranges are specifically included as if explicitly written out. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 The structure of the positive electrode sheet in an example of the present application is shown. DETAILED DESCRIPTION

[0016] The specific embodiments of the present application are described in detail below. It should be understood that the specific embodiments described herein are merely illustrative and explanatory of the present application and are not intended to limit the present application.

[0017] The present application provides a battery, which comprises a positive electrode sheet and an electrolyte. The positive electrode sheet comprises a positive electrode current collector and a coating layer located at the edge of the surface of at least one side of the positive electrode current collector in the length direction; the coating layer comprises filler particles, and the filler particles comprise at least one of inorganic particles and nitrogen-containing particles. Figure 1 The structure of the positive electrode sheet in an example of the present application is shown. As can be seen from the figure, the positive electrode sheet comprises a positive electrode current collector 1 and a coating layer 2 located at the edge of the surface of one side of the positive electrode current collector 1 in the length direction. It can be understood that, Figure 1 The present application only gives the case of setting the coating layer at the edge of the surface of one side of the positive electrode current collector in the length direction, which does not mean that the coating layer can only be set at the edge of the surface of one side of the positive electrode current collector in the length direction. The coating layer can also be set at the edge of the surface of both sides of the positive electrode current collector in the length direction.

[0018] In the present application, the inorganic particles comprise at least one of bormite, aluminum oxide and magnesium oxide. The nitrogen-containing particles comprise at least one of melamine, melamine cyanurate, melamine polyphosphate, melamine trithiocyanate and melamine formaldehyde resin.

[0019] In the present application, the electrolyte includes a non-fluorinated cyclic carbonate and a fluoroethyl acetate. The non-fluorinated cyclic carbonate includes propylene carbonate and optionally vinyl carbonate. The "optionally" means that the electrolyte can include vinyl carbonate or can not include vinyl carbonate. The fluoroethyl acetate means a substance in which a fluorine atom is substituted at any position of ethyl acetate.

[0020] In the present application, the content ratio of the non-fluorinated cyclic carbonate is C1≤25% based on the total mass of the electrolyte, for example, 25%, 24%, 23%, 22%, 21%, 20%, 19%, 18%, 17%, 16%, 15%, 14%, 13%, 12%, 11%, 10%, 9%, 8%, 7%, 6%, or 5%.

[0021] In an example, C1≤20.1%.

[0022] In the present application, the content ratio of propylene carbonate is C11 of 3.1%-24.9% (for example, 3.1%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, or 24.9%) and the content ratio of vinyl carbonate is C12 of 0%-5% (for example, 0%, 1%, 2%, 3%, 4%, or 5%) based on the total mass of the electrolyte.

[0023] In an example, C11 is 5.1%-17.4%.

[0024] In an example, the mass content ratio of propylene carbonate is greater than the mass content ratio of vinyl carbonate in the electrolyte.

[0025] In the present application, the content ratio of the fluoroethyl acetate is C2 of 20.2%-70%, for example, 20.2%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, or 70%.

[0026] In an example, C2 is 25.1%-65%.

[0027] In an example, C2 is 29.3%-60%.

[0028] In the present application, the mass content ratio C1 of the non-fluorinated cyclic carbonate, the mass content ratio C11 of propylene carbonate, the mass content ratio C12 of vinyl carbonate, and the mass content ratio C2 of the fluoroethyl acetate in the electrolyte can be obtained by a method conventional in the art, for example, gas chromatography (GC).

[0029] In the present application, the fluoroacetic acid ethyl ester includes 2,2-difluoroacetic acid ethyl ester (DFEA) and / or 2,2-difluoroacetic acid ethyl ester.

[0030] In an example, the fluoroacetic acid ethyl ester includes 2,2-difluoroacetic acid ethyl ester.

[0031] In the present application, the average thickness of the coating layer is 3 μm-20 μm, for example, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm or 20 μm. The size of the coating layer in the width direction of the positive electrode sheet is 0.1 mm-10 mm, for example, 0.1 mm, 0.5 mm, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm or 10 mm.

[0032] In an example, the average thickness of the coating layer is 5 μm-20 μm.

[0033] In an example, the size of the coating layer in the width direction of the positive electrode sheet is 0.2 mm-5 mm.

[0034] In the present application, the average thickness of the coating layer and the size of the coating layer in the width direction of the positive electrode sheet can be tested by conventional methods in the art, for example, randomly selecting at least 10 points on the coating layer, measuring the thickness of the coating layer and the size in the width direction at each point, and taking the average value.

[0035] In the present application, the average particle size D of the filler particles is 0.05 μm-5 μm, for example, 0.05 μm, 0.1 μm, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm or 5 μm. The average particle size D of the filler particles can be tested by conventional methods in the art, for example, after discharging the battery to 0% SOC, disassembling and taking out the positive electrode sheet, soaking in dimethyl carbonate (DMC) solvent for 12 h, then rinsing with DMC solvent to remove the lithium salt attached to the positive electrode sheet, cutting the positive electrode sheet using argon ion grinder CP, and then observing using a scanning electron microscope (SEM). In the electron microscope image, randomly select at least 10 filler particles, measure the particle size of each particle, and take the average value. If the number of particles in the electron microscope image is less than 10, take another image until 10 particles are measured. When the particles in the image are regular circles, the particle size is the diameter of the regular circle. When the particles in the image are not "regular circles", connect any two points on the edge of the particle to form a straight line segment inside the particle, and select the longest straight line segment inside the particle as the particle size.

[0036] In an example, D is 0.1 μm-3 μm.

[0037] In the present application, the average particle size D (in units of μm) of the filler particles and the mass content ratio C2 of the ethyl fluoroacetate in the electrolyte satisfy: 1≤D / C2≤18, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17 or 18.

[0038] In an example, 2.5≤D / C2≤8.5.

[0039] The average particle size of the filler particles not only reflects the number of active sites per unit area of the particles, but also affects the length of the lithium ion transmission path; and the mass content ratio of the ethyl fluoroacetate in the electrolyte affects the degree of chemical modification of the interface and the rate of desolvation. Therefore, when the two satisfy the above relationship, the transmission path of lithium ions can be optimized, and the occurrence of lithium precipitation can be further inhibited by regulating the solvation structure, as follows: As mentioned earlier, inorganic particles (such as bormite or alumina) can interact with ethyl fluoroacetate, thereby adsorbing ethyl fluoroacetate on the surface of inorganic particles. When the ratio of the two is within a certain range, the thickness of the ethyl fluoroacetate adsorbed on the inorganic particles matches the particle size, and a continuous high-speed channel for lithium ions can be formed. When the ratio of the two is too small (for example, less than 1), the inorganic particle surface is overloaded with ethyl fluoroacetate molecules, which blocks the pores and causes lithium ion transmission to be blocked, easily leading to lithium precipitation; and when the ratio of the two is too large (for example, greater than 18), the high-speed channel for lithium ions is discontinuous, and the local current is concentrated, also easily causing lithium precipitation. The nitrogen-containing group in the nitrogen-containing particle can form a hydrogen bond network with ethyl fluoroacetate, which destroys the solvation sheath of lithium ions. When the ratio of the two is within a certain range, the network formed by adsorbing ethyl fluoroacetate can just cover the active sites on the surface of the particles, thereby reducing the desolvation energy barrier. When the ratio of the two is too small (for example, less than 1), too much ethyl fluoroacetate exceeds the coordination ability of the nitrogen-containing group, resulting in a dense hydrogen bond network that blocks the lithium ion transmission channel; and when the ratio of the two is too large (for example, greater than 18), the coordination ability of the nitrogen-containing group is not fully activated, and the lithium ion is still strongly bound by the carbonate solvent, the desolvation energy barrier is high, and lithium precipitation is easily caused.

[0040] In the present application, the electrolyte further comprises a first lithium salt. The first lithium salt comprises lithium bisfluorosulfonylimide (LiFSI) and / or lithium bis(trifluoromethylsulfonyl)imide (LiTFSI). LiFSI and LiTFSI have strong thermal stability and are not easy to hydrolyze to generate HF; and have a high lithium ion transference number, which can reduce the risk of lithium precipitation of the battery under high-rate cycling.

[0041] In the present application, the content ratio C3 of the first lithium salt is 0.5%-12.3% based on the total mass of the electrolyte, for example, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12% or 12.3%.

[0042] In an example, C3 is 1.1%-9.5%.

[0043] In the present application, the electrolyte further comprises a second lithium salt. The second lithium salt comprises lithium difluorophosphate (LiPO2F2). LiPO2F2 can reduce the internal resistance of the battery, thereby improving the charge and discharge efficiency and inhibiting the problem of lithium precipitation at low temperature of the battery.

[0044] In the present application, the content ratio C4 of the second lithium salt is 0.01%-2.05% based on the total mass of the electrolyte, for example, 0.01%, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2% or 2.05%.

[0045] In the present application, the electrolyte further comprises a third lithium salt. The third lithium salt comprises lithium hexafluorophosphate (LiPF6).

[0046] In the present application, the content ratio C5 of the third lithium salt is 6%-18% based on the total mass of the electrolyte, for example, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17% or 18%.

[0047] In the present application, the content ratio C1 of the first lithium salt in the electrolyte, the content ratio C2 of the second lithium salt in the electrolyte and the content ratio C3 of the third lithium salt in the electrolyte can be tested by a method conventional in the art, for example, ion chromatography (IC).

[0048] In the present application, the electrolyte further comprises 1,3-propane sultone and / or tripropargyl phosphate (TPP). The addition of 1,3-propane sultone and / or TPP in the electrolyte can make the battery form films in different voltages in sequence or alternately with the solvent during the first formation, so that the interface film formed between the positive electrode and the negative electrode has high cross-linking degree, is dense and has good toughness and is not easy to break down and dissolve during the later cycle process, thereby further increasing the cycle stability of the battery at high temperature.

[0049] In this invention, based on the total mass of the electrolyte, the content percentage (C6) of 1,3-propanesulfonyl lactone is 0.82%-5.68%, for example, 0.82%, 1%, 2%, 3%, 4%, 5%, or 5.68%. Based on the total mass of the electrolyte, the content percentage (C7) of triargyl phosphate is 0.01%-1.99%, for example, 0.01%, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, or 1.99%.

[0050] In one instance, C7 is 0.1%–0.9%.

[0051] In this invention, the mass content ratio of 1,3-propanesulfonate lactone (C6) and the mass content ratio of triargyl phosphate (C7) in the electrolyte can be obtained by conventional methods in the art, such as GC.

[0052] In this invention, the electrolyte further includes fluoroethylene carbonate (FEC). Based on the total mass of the electrolyte, the FEC content is 5%-20%, for example, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, or 20%.

[0053] In this invention, the electrolyte further includes a fluorosulfonamide compound. The fluorosulfonamide compound includes...

[0054] At least one of them.

[0055] In this invention, based on the total mass of the electrolyte, the content of the fluorosulfonamide compound is 1%-30%, for example, 1%, 5%, 10%, 15%, 20%, 25% or 30%.

[0056] In one example, the content of the fluorosulfonamide compound is 2%-15% based on the total mass of the electrolyte.

[0057] In this invention, the electrolyte further includes Based on the total mass of the electrolyte, The content percentage is 0.1%-3%, for example, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5% or 3%.

[0058] In this invention, the mass percentage of the fluorosulfonamide compound in the electrolyte and The mass content ratio in the electrolyte can be tested by a method conventional in the art, for example, GC.

[0059] In the present application, the electrolyte can further include an organic solvent conventionally added in the art. The organic solvent includes at least one of propyl propionate (PP), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC), for example.

[0060] In the present application, the positive electrode sheet further includes a positive electrode active coating layer, which is disposed adjacent to the coating layer. The positive electrode active coating layer includes a positive electrode active material; the positive electrode active material includes a nickel-cobalt-manganese ternary material and / or a lithium iron phosphate.

[0061] In an example, the positive electrode active material includes a nickel-cobalt-manganese ternary material. The chemical formula of the nickel-cobalt-manganese ternary material is LiNi x Co y Mn z M a O2, wherein 0.8≤x≤0.95 (for example, 0.8, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.9, 0.91, 0.92, 0.93, 0.94, or 0.95), 0.01≤y≤0.2 (for example, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, or 0.2), 0.01≤z≤0.18 (for example, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, or 0.18), 0<a≤0.1 (for example, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, or 0.1); M includes at least one of Al, Mg, Y, W, B, Zr, Ti, Sr, La, and Nb.

[0062] In an example, 0.85≤x≤0.93.

[0063] In an example, the outer surface of the nickel-cobalt-manganese ternary material has a cladding layer. The cladding layer includes at least one of the elements Al, Zr, B, Nb, and W.

[0064] In the present application, the thickness of the coating layer is 1 nm-40 nm, for example, 1 nm, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm or 40 nm.

[0065] In an example, the thickness of the coating layer is 2 nm-25 nm.

[0066] The coating layer has a great influence on the gas production of the battery under high temperature conditions. Therefore, when the thickness of the coating layer is too thin (for example, less than 1 nm), the effect of the coating layer may not be effectively exerted, resulting in an increase in the gas production of the battery under high temperature conditions; and when the thickness of the coating layer is too thick (for example, greater than 40 nm), although the effect of the coating layer can be effectively exerted, the too thick coating layer will result in a low energy density of the battery; and the too thick coating layer will weaken the deintercalation speed of lithium ions, thereby exacerbating the lithium precipitation problem of the negative plate under low temperature discharge of the battery.

[0067] In the present application, the thickness of the coating layer can be tested by conventional methods in the art, for example, after discharging the battery to 0% SOC, disassembling and taking out the positive plate, soaking in DMC solvent for 12 h, then rinsing with DMC solvent to remove the lithium salt attached to the positive plate, cutting the positive plate using an argon ion grinder CP, and then observing using a transmission electron microscope (TEM); in the electron microscope image, at least 20 point positions on the coating layer are selected (the coating layer of the same particle can be selected, or the coating layers of different particles can be selected), the thickness of the coating layer at each point position is measured, and the average value is taken.

[0068] In the present application, the nickel-cobalt-manganese ternary material includes single crystal particles and / or polycrystalline particles.

[0069] In an example, the nickel-cobalt-manganese ternary material is single crystal particles. Since the gas production of single crystal particles is lower than that of polycrystalline particles under high temperature conditions, when the nickel-cobalt-manganese ternary material is single crystal particles, the gas production of the battery under high temperature conditions can be further reduced. And the transmission speed of lithium ions in single crystal particles is significantly higher than that in polycrystalline particles, so when the nickel-cobalt-manganese ternary material is single crystal particles, the deintercalation speed of lithium ions can be reduced during low temperature discharge, thereby further improving the lithium precipitation problem.

[0070] In the present application, the average particle size of the nickel-cobalt-manganese ternary material is 0.5-15 μm, for example, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm or 15 μm. Under the interface protection of the coating layer, when the average particle size of the nickel-cobalt-manganese ternary material is within a certain range, the nickel-cobalt-manganese ternary material has a higher specific surface area, so that the material can better contact with the electrolyte, reduce the internal resistance of the battery during rapid charging and discharging, improve the charging and discharging rate, and further reduce the risk of lithium precipitation on the negative electrode during low-temperature discharging.

[0071] In the present application, the average particle size of the nickel-cobalt-manganese ternary material can be tested by conventional methods in the art, for example, after discharging the battery to 0% SOC, disassembling and taking out the positive electrode sheet, soaking in DMC solvent for 12 h, then rinsing with DMC solvent to remove the lithium salt attached to the positive electrode sheet, cutting the positive electrode sheet using an argon ion grinder CP, and then observing using a scanning electron microscope (SEM). In the electron micrograph, at least 10 nickel-cobalt-manganese ternary material particles are randomly selected, the particle size of each particle is measured, and the average value is taken. If the number of particles in the electron micrograph is less than 10, another electron micrograph is taken until 10 particles are measured. When the particles in the electron micrograph are regular circles, the particle size of the particles is the diameter of the regular circles. When the particles in the electron micrograph are not "regular circles", connecting any two points on the edge of the particle to form a straight line segment inside the particle, and selecting the longest straight line segment inside the particle as the particle size.

[0072] In an example, the positive electrode active material comprises lithium iron phosphate.

[0073] In the present application, the lithium iron phosphate contains at least one of the elements Ti, Al, Mg, Co, Zr, Mn, Sr, La and Nb. The lithium iron phosphate has a long service life and good thermal stability, which can effectively reduce the attenuation of the battery under harsh conditions such as high temperature and deep discharge. Especially when used in combination with the ternary nickel-cobalt-manganese material, it can improve the performance of the battery under high load or high temperature environment, and also balance high energy density and high safety.

[0074] In an example, the lithium iron phosphate comprises a single crystal.

[0075] In the present application, the average particle size of the lithium iron phosphate is 0.1 μm-2 μm, for example, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm or 2 μm. The testing method of the average particle size of the lithium iron phosphate refers to that of the nickel-cobalt-manganese ternary material, which is not described herein.

[0076] In the present application, the median particle size Dv50 of the lithium iron phosphate is 0.1 μm-2 μm, for example, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm or 2 μm. The particle size Dv90 of the lithium iron phosphate is ≤2.5 μm. The median particle sizes Dv50 and Dv90 of the lithium iron phosphate can be tested by the conventional method in the art, for example, using a laser particle size analyzer.

[0077] In the present application, the positive electrode active coating further comprises a positive electrode conductive agent and / or a positive electrode binder. The positive and negative electrode conductive agents comprise at least one of conductive carbon black, acetylene black, ketjen black, conductive graphite and carbon nanotubes (including at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes) and carbon fibers. The positive electrode binder comprises at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene butadiene rubber, polytetrafluoroethylene and polyethylene oxide.

[0078] In the present application, the content of the positive electrode active material accounts for 80%-99.8% (for example, 80%, 82%, 84%, 86%, 88%, 90%, 92%, 94%, 96%, 98%, 99% or 99.8%) of the total mass of the positive electrode active coating, the content of the positive electrode conductive agent accounts for 0.1%-10% (for example, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5% or 0.1%) of the total mass of the positive electrode active coating, and the content of the positive electrode binder accounts for 0.1%-10% (for example, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5% or 0.1%) of the total mass of the positive electrode active coating.

[0079] In the present application, the battery further comprises a negative electrode sheet. The negative electrode sheet comprises a negative electrode current collector and a negative electrode active coating located on at least one side surface of the negative electrode current collector, wherein the negative electrode active coating comprises a negative electrode active material, and the negative electrode active material comprises a silicon-based material.

[0080] In the present application, the silicon-based material includes at least one of silicon element, silicon-oxygen, silicon-carbon and silicon alloy. The silicon-oxygen refers to a material containing silicon element and oxygen element, and the silicon-carbon refers to a material containing silicon element and carbon element.

[0081] In the present application, the sphericity of the silicon-based material is 0.8-0.99, for example, 0.8, 0.85, 0.9, 0.95 or 0.99. The sphericity of the silicon-based material can be tested by a method conventional in the art, for example, discharging the battery to 0% SOC, disassembling to take out the negative electrode sheet, cutting the negative electrode sheet using an argon ion grinder CP, observing in a SEM device using backscattering imaging mode; finding a silicon-based material particle with a continuous and smooth contour, connecting any two points on the particle edge to form a straight line segment inside the particle, selecting the longest straight line segment in the particle, and recording its length as Z1; taking the midpoint of the longest straight line segment, drawing a straight line through the midpoint to form a straight line segment with endpoints on the particle edge, selecting the shortest straight line segment, and recording its length as Z2. The sphericity of the particle is Z2 / Z1. At least 5 silicon-based material particles are selected, and the sphericity is measured and averaged.

[0082] In an example, the silicon-based material includes silicon-carbon. The silicon-carbon material includes a porous carbon matrix and silicon particles in the pores of the porous carbon matrix.

[0083] In the present application, the silicon-based material contains Ca element. The content of Ca element accounts for 10-500 ppm, for example, 10 ppm, 20 ppm, 30 ppm, 40 ppm, 50 ppm, 60 ppm, 70 ppm, 80 ppm, 90 ppm, 100 ppm, 150 ppm, 200 ppm, 250 ppm, 300 ppm, 350 ppm, 400 ppm, 450 ppm or 500 ppm, based on the total mass of the silicon-based material. When the silicon-based material further contains Ca element, not only the conductivity of the negative electrode sheet can be improved, but also the diffusion channel of Li+ can be widened, thereby further improving the lithium precipitation problem of the edge and middle part of the negative electrode sheet. +

[0084] In an example, the content of Ca element accounts for 10-300 ppm, based on the total mass of the silicon-based material.

[0085] ​In the present application, the mass content of Ca element in the silicon-based material can be tested by conventional methods in the art, for example, discharging the battery to 0% SOC, disassembling and taking out the negative electrode sheet, soaking in DMC solvent for 12 h, then rinsing with DMC solvent to remove the lithium salt attached to the negative electrode sheet, drying, then high-temperature treatment of the negative electrode sheet at 400°C in an inert atmosphere for 2 h (for example, in a tube furnace, under nitrogen or argon atmosphere), the negative electrode active coating can be peeled off from the negative electrode current collector, and the negative electrode active coating is collected as a test sample. Using a thermal gravimetric analyzer (for example, TGA 550 thermal gravimetric analyzer), the sample amount is 5 mg-15 mg, under air or oxygen atmosphere, the temperature is raised from room temperature (25°C) to 900°C at a rate of 10°C / min, and the residual substance is tested using inductively coupled plasma (ICP), and the mass content of Ca element in the silicon-based material is calculated.

[0086] In an example, the mass content of silicon element in the silicon-carbon is 35%-75%, for example, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70% or 75%. The mass content of silicon element in the silicon-carbon can be tested by conventional methods in the art, for example, discharging the battery to 0% SOC, disassembling and taking out the negative electrode sheet, cutting the negative electrode sheet using argon ion grinder CP, observing the silicon-carbon material in the SEM device using backscattering imaging mode to maximize the magnification; using an energy dispersive spectrometer (EDS) to scan the cross-section of the silicon-carbon particles, the area of the scan should not be less than 50% of the cross-section of the particles, and the scanning range should be completely within the cross-section of the particles, and the mass content of silicon element is calculated. At least 10 particles are selected for measurement respectively, and the average value is taken.

[0087] In the present application, the average particle size of the silicon-carbon is 5 μm-15 μm, for example, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm or 15 μm. The specific surface area of the silicon-carbon is 1.5 m 2 / g-3 m 2 / g, for example, 1.5 m 2 / g, 2 m 2 / g, 2.5 m 2 / g or 3 m 2 / g. By adjusting the average particle size and specific surface area of the silicon-carbon, the size and morphology of the silicon-carbon particles can be limited, thereby reducing the swelling effect and further reducing the risk of high-temperature gas production.

[0088] In the present application, the average particle size of the silicon-carbon can be tested by a method conventional in the art, for example, after discharging the battery to 0% SOC, disassembling and taking out the negative electrode sheet, soaking in DMC solvent for 12 h, then rinsing with DMC solvent to remove the lithium salt attached to the negative electrode sheet, using an argon ion grinder CP to cut the negative electrode sheet, then using SEM to observe, in the electron microscope image, randomly selecting at least 10 silicon-carbon particles, measuring the particle size of each particle, and taking the average. If the number of particles in the electron microscope image is less than 10, then take another image until 10 particles are measured. When the particles in the image are regular circles, the particle size is the diameter of the regular circle. When the particles in the image are not "regular circles", connect any two points on the edge of the particle to form a straight line segment inside the particle, and select the longest straight line segment inside the particle as the particle size.

[0089] In the present application, the negative electrode active material further comprises a carbon-based material, which comprises at least one of artificial graphite, natural graphite, mesocarbon microbeads, soft carbon and hard carbon.

[0090] In the present application, the content of the silicon-based material accounts for 5%-80% of the total mass of the negative electrode active material, for example, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70% or 80%.

[0091] In the present application, the negative electrode active coating further comprises a negative electrode conductive agent and / or a negative electrode binder. The negative electrode conductive agent comprises at least one of conductive carbon black, acetylene black, Ketjen black, conductive graphite and carbon nanotubes (including at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes) and carbon fibers. The negative electrode binder comprises at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, butadiene rubber, polytetrafluoroethylene and polyethylene oxide.

[0092] In the present application, the content of the negative electrode active material accounts for 80%-99.8% (for example, 80%, 82%, 84%, 86%, 88%, 90%, 92%, 94%, 96%, 98%, 99% or 99.8%) of the total mass of the negative electrode active coating, the content of the negative electrode conductive agent accounts for 0.1%-10% (for example, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5% or 0.1%) and the content of the negative electrode binder accounts for 0.1%-10% (for example, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5% or 0.1%).

[0093] In the present application, the positive electrode tab further comprises a positive electrode ear, and the negative electrode tab further comprises a negative electrode ear. The positive electrode ear comprises at least one of nickel, nickel alloy and nickel-plated copper, for example. The positive electrode ear with the specific composition has higher conductivity and better corrosion resistance. The negative electrode ear comprises copper and / or nickel-plated copper, for example. The negative electrode ear with the specific composition has better conductivity and can effectively avoid side reactions between the negative electrode and the electrolyte.

[0094] In the present application, the thickness of the positive electrode ear and the thickness of the negative electrode ear are each independently 0.1 mm-0.3 mm, for example 0.1 mm, 0.2 mm or 0.3 mm. The width of the positive electrode ear and the width of the negative electrode ear are each independently 5 mm-10 mm, for example 5 mm, 6 mm, 7 mm, 8 mm, 9 mm or 10 mm. The length of the positive electrode ear and the length of the negative electrode ear are each independently 10 mm-50 mm, for example 10 mm, 20 mm, 30 mm, 40 mm or 50 mm.

[0095] In an example, the number of the positive electrode ear is greater than or equal to 2.

[0096] In an example, the number of the negative electrode ear is greater than or equal to 2.

[0097] In an example, the positive electrode ear is located on the same side as the coating layer.

[0098] When the number of the positive electrode ear and / or the number of the negative electrode ear is greater than or equal to 2, the battery has a multi-tab structure. At this time, the positive electrode ear and / or the negative electrode ear can more effectively conduct current, especially when the positive electrode ear is located on the side where the coating layer is arranged, which can improve the charge and discharge efficiency of the battery and further reduce the risk of lithium precipitation at the edge of the negative electrode tab at low temperature discharge. In addition, the mechanical strength of the positive electrode ear and / or the negative electrode ear as a whole can be enhanced to prevent problems such as tab breakage and welding failure, ensuring long-term reliable use of the battery. In addition, since the battery will come into contact with the electrolyte during use, when the number of the positive electrode ear and / or the number of the negative electrode ear is greater than or equal to 2, the positive electrode ear and / or the negative electrode ear can effectively resist corrosion by the electrolyte, prolong the service life of the battery and ensure the stability of the battery in different environments.

[0099] In the present application, the battery further comprises a separator.

[0100] In an example, the separator comprises a substrate layer and a glue layer located on at least one outer surface of the separator. The glue layer comprises polyvinylidene fluoride (PVDF) and / or polymethyl methacrylate (PMMA).

[0101] In the present application, the average particle size of the PVDF is 0.1 μm-3 μm, for example, 0.1 μm, 0.5 μm, 1 μm, 2 μm or 3 μm. The average particle size of the PVDF can be tested by a method conventional in the art, for example, after discharging the battery to 0% SOC, disassembling to take out the separator, soaking in DMC solvent for 12 h, then rinsing with DMC solvent to remove the lithium salt attached to the separator, cutting the separator using an argon ion grinder CP, then observing using SEM, in the electron microscope image, randomly selecting at least 10 PVDF particles, measuring the particle size of each particle, and taking the average. If the number of particles in the electron microscope image is less than 10, then another image is taken until 10 particles are measured. When the particles in the image are regular circles, the particle size is the diameter of the regular circle; when the particles in the image are not "regular circles", connecting any two points on the edge of the particle to form a straight line segment inside the particle, selecting the longest straight line segment inside the particle as the particle size.

[0102] In the present application, the coverage of the adhesive layer on the outer surface of the separator is 15%-75%, for example, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70% or 75%.

[0103] In an example, the coverage of the adhesive layer on the outer surface of the separator is 30%-70%.

[0104] In the present application, the coverage of the adhesive layer on the outer surface of the separator can be tested by a method conventional in the art, for example, calculating the coverage by SEM image, the specific steps being as follows: on the side surface of the separator coated with the adhesive layer, randomly taking an area of 100 μm x 100 μm, dividing this area into 100 x 100 uniform squares, calculating the total number of squares occupied by the adhesive layer X (when the area of the square occupied by the adhesive layer is greater than or equal to 50%, then it is considered to occupy 1 square; when the area of the square occupied by the adhesive layer is less than 50%, it is considered not to be occupied), then the coverage = X x 100% / (100 x 100), repeating the above operation 5 times, and taking the average as the coverage of the adhesive layer on the outer surface of the separator.

[0105] When the coverage of the adhesive layer on the outer surface of the separator is within a certain range, the adhesive layer with a certain composition not only can provide protection to prevent the separator from melting or being damaged at high temperature, but also can reduce the heat diffusion of the separator, improve heat dissipation, reduce the heat accumulation at the interface of the positive / negative electrode, reduce the side reaction at the interface of the positive / negative electrode, improve high-temperature gas production, and prevent thermal runaway of the battery by controlling the coverage of the adhesive layer. In addition, the separator of the present application has high compatibility with the electrolyte, because the swelling of ethyl fluoroacetate to PMMA and / or PVDF is smaller than that of EC, by controlling the content of EC in the electrolyte, the adhesion of the separator to the interface of the positive / negative electrode sheet can be ensured, the interface stability can be maintained, and the high-temperature gas production can be further reduced.

[0106] In an example, the separator further comprises a functional layer. The functional layer is located on at least one side surface of the substrate layer. The functional layer comprises at least one of aluminum oxide, barite, melamine, melamine cyanurate, melamine thiocyanate, zirconium oxide, and calcium carbonate.

[0107] In an example, the separator comprises the substrate layer, the functional layer located on one side surface of the substrate layer, the adhesive layer located on the other side surface of the substrate layer, and the adhesive layer located on the outer surface of the functional layer.

[0108] In an example, the functional layer faces the positive electrode sheet.

[0109] In the present application, the thickness of the functional layer is 0.5-8 μm, for example, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, or 8 μm. The thickness of the adhesive layer is 0.3-5 μm, for example, 0.3 μm, 1 μm, 2 μm, 3 μm, 4 μm, or 5 μm. The thickness of the functional layer and the thickness of the adhesive layer refer to the single-layer thickness of the thickness of the functional layer and the thickness of the adhesive layer.

[0110] In the present application, the thickness of the functional layer and the thickness of the adhesive layer can be obtained by conventional test methods in the art, for example, after discharging the battery to 0% SOC, disassembling and taking out the separator, soaking in DMC solvent for 12 h, then washing with DMC to remove the lithium salt attached to the separator, selecting the area of the separator beyond the negative electrode sheet in the battery, polishing the cross section of the separator with an argon ion polishing device, observing with SEM, and observing the interface between the functional layer and the adhesive layer in the SEM image, measuring the thickness of the functional layer and the adhesive layer according to the interface, respectively, and taking the average value after measuring 10 different sites.

[0111] In the present application, the battery can comprise a wound cell, i.e., the positive electrode sheet, the separator, and the negative electrode sheet are stacked and wound to form a wound cell; or a laminated cell, i.e., the positive electrode sheet, the separator, and the negative electrode sheet are stacked to form a laminated cell.

[0112] It should be noted that the "first", "second" and the like in the present application are only used to distinguish different substances or use methods, and do not represent the difference in order.

[0113] The present application will be described in detail by the following examples. The examples described in the present application are only a part of the examples of the present application, not all examples. Based on the examples in the present application, all other examples obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0114] In the following examples, the materials used are commercially available analytical pure without special instructions.

[0115] The following examples are used to illustrate the lithium ion secondary battery of the present application.

[0116] Example 1

[0117] The battery is prepared according to the following method:

[0118] (1) Preparation of positive electrode sheet

[0119] The nickel cobalt manganese ternary material (chemical formula LiNi 0.87 Co 0.04 Mn 0.05 Mg 0.04 O2), positive electrode conductive agent (conductive carbon black and carbon nanotube mixed in a mass ratio of 3:1) and polyvinylidene fluoride are mixed uniformly in a mass ratio of 97.6:1.35:1.05, placed in N-methyl pyrrolidone (NMP), stirred uniformly, and a positive electrode slurry is prepared; the barite (average particle size D is 2.5 μm) and polyvinylidene fluoride are mixed uniformly in a mass ratio of 95:5, placed in NMP, stirred uniformly, and a coating slurry is prepared; the positive electrode slurry is uniformly coated on both sides of the surface of the aluminum foil, dried; then the coating slurry is coated along the length direction of the aluminum foil in contact with the positive electrode active coating, and sequentially dried, rolled, and cut; a positive electrode sheet is obtained.

[0120] The average thickness of the coating is 12 μm, and the size of the coating along the width direction of the positive electrode sheet is 2.7 mm.

[0121] The outer surface of the nickel cobalt manganese ternary material has a coating layer, and the coating layer comprises element Al; the thickness of the coating layer is 15 nm.

[0122] The nickel cobalt manganese ternary material is a single crystal particle.

[0123] The number of positive electrode ears is greater than or equal to 2.

[0124] (2) Preparation of negative electrode sheet

[0125] The negative active material (artificial graphite and silicon carbon mixed in a mass ratio of 3:1), conductive carbon black, butadiene rubber, and sodium carboxymethyl cellulose are mixed uniformly in a mass ratio of 95:2:1.5:1.5, deionized water is added, and the mixture is fully stirred to form a uniform negative electrode slurry; the negative electrode slurry is coated on both sides of the copper foil surface, dried, rolled, cut, and a negative electrode sheet is obtained;

[0126] The silicon-carbon contains Ca elements, and the mass content of Ca elements in the silicon-carbon accounts for 196 ppm;

[0127] The number of negative tabs is greater than or equal to 2.

[0128] (3) Preparation of electrolyte

[0129] In the glove box (H2O<0.01 ppm, O2<0.01 ppm, Ar atmosphere), PC and DFEA are mixed uniformly in propyl propionate (PP), and the first lithium salt (LiFSI), the second lithium salt (LiPO2F2), and the third lithium salt (LiPF6) are added, and then PS, TPP, and 8% FEC based on the total mass of the electrolyte are added, and stirred uniformly, and after passing the water content and free acid detection, the electrolyte is obtained;

[0130] C11 is 11.8%, C12 is 0%, C1 is 11.8%; C2 is 43.8%, C3 is 5.3%, C4 is 1.02%, C5 is 18%, C6 is 3.4%, and C7 is 0.43%.

[0131] (4) Preparation of the separator

[0132] The bormite, butadiene rubber, and lithium polyacrylate are mixed uniformly in a mass ratio of 96:2:2, and NMP is added to obtain a functional layer slurry; the functional layer slurry is coated on one side of the polyethylene film surface, dried to obtain a functional layer; and a glue layer (including PVDF, and the solvent is deionized water) is coated on the outer surface of the functional layer and the other side of the polyethylene film to obtain a separator;

[0133] The average particle size of the PVDF is 1.5 μm;

[0134] The coverage of the glue layer on the outer surface of the separator is 55%;

[0135] The thickness of the glue layer is 2.2 μm, and the thickness of the functional layer is 4.5 μm.

[0136] (5) Preparation of the battery

[0137] The negative electrode sheet prepared in step (2), the positive electrode sheet prepared in step (1) and a separator (polyethylene film) are wound into a core in a predetermined procedure, the core is loaded into an aluminum plastic film shell, a PET film is attached outside the aluminum plastic film shell, the electrolyte prepared in step (3) is injected, and a battery is prepared through procedures such as vacuum sealing, standing, formation, sorting, and two-sealing;

[0138] D / C2 is 5.71.

[0139] Example 2

[0140] The battery is prepared according to the following method:

[0141] (1) Preparation of a positive electrode sheet

[0142] The nickel-cobalt-manganese ternary material (LiNi 0.85 Co 0.1 Mn 0.03 Al 0.02 O2), a positive electrode conductive agent (a mixture of conductive carbon black and carbon nanotubes in a mass ratio of 3:1) and polyvinylidene fluoride are mixed in a mass ratio of 97.6:1.35:1.05, and are uniformly placed in N-methyl pyrrolidone (NMP) and stirred uniformly to prepare a positive electrode slurry; melamine cyanurate (with an average particle size D of 0.8 μm) and polyvinylidene fluoride are uniformly mixed in a mass ratio of 95:5, and are uniformly placed in NMP and stirred to prepare a coating slurry; the positive electrode slurry is uniformly coated on both sides of the surface of an aluminum foil, and is dried; then the coating slurry is coated along the length direction of the aluminum foil and in contact with the positive electrode active coating, and is sequentially subjected to drying, rolling and slitting processes; and a positive electrode sheet is obtained.

[0143] The average thickness of the coating is 5 μm, and the size of the coating along the width direction of the positive electrode sheet is 5 mm.

[0144] The outer surface of the nickel-cobalt-manganese ternary material has a coating layer, and the coating layer comprises element B; the thickness of the coating layer is 2 nm.

[0145] The nickel-cobalt-manganese ternary material is a single crystal particle.

[0146] The number of positive electrode tabs is greater than or equal to 2.

[0147] (2) Preparation of a negative electrode sheet

[0148] The negative electrode active material (a mixture of artificial graphite and silicon carbon in a mass ratio of 3:1), conductive carbon black, butadiene rubber and sodium carboxymethyl cellulose are uniformly mixed in a mass ratio of 95:2:1.5:1.5, deionized water is added, and the mixture is fully stirred to form a uniform negative electrode slurry; the negative electrode slurry is coated on both sides of the surface of a copper foil, is dried, is rolled, is cut, and a negative electrode sheet is obtained.

[0149] The silicon-carbon contains Ca element, and the mass content of Ca element in the silicon-carbon is 53 ppm.

[0150] The number of negative tabs is greater than or equal to 2.

[0151] (3) Preparation of electrolyte

[0152] In a glove box (H2O < 0.01 ppm, O2 < 0.01 ppm, Ar atmosphere), PC, EC and DFEA were mixed uniformly in propyl propionate (PP), and the first lithium salt (LiTFSI), the second lithium salt (LiPO2F2) and the third lithium salt (LiPF6) were added thereto, and then PS, TPP and 12% FEC based on the total mass of the electrolyte were added and stirred uniformly. After passing the water and free acid detection, the electrolyte was obtained.

[0153] In the formula, C11 is 5.1%, C12 is 5%, C1 is 10.1%, C2 is 29.3%, C3 is 9.5%, C4 is 0.01%, C5 is 6%, C6 is 5.68%, and C7 is 0.99%.

[0154] (4) Preparation of separator

[0155] Aluminum oxide, butadiene rubber and lithium polyacrylate were mixed uniformly according to a mass ratio of 96:2:2, and NMP was added to obtain a functional layer slurry. The functional layer slurry was coated on one side surface of a polyethylene film, and dried to obtain a functional layer. A glue layer (containing PMMA, and deionized water as a solvent) was coated on the outer surface of the functional layer and the other side surface of the polyethylene film to obtain a separator.

[0156] In the formula, the average particle size of PVDF is 0.3 μm.

[0157] The coverage of the glue layer on the outer surface of the separator is 30%.

[0158] The thickness of the glue layer is 0.8 μm, and the thickness of the functional layer is 6.3 μm.

[0159] (5) Preparation of battery

[0160] The negative electrode sheet prepared in step (2), the positive electrode sheet prepared in step (1) and the separator (polyethylene film) were wound into a core according to a predetermined procedure, the core was loaded into an aluminum plastic film shell, and then a PET film was attached outside the aluminum plastic film shell. The electrolyte prepared in step (3) was injected, and the battery was prepared after vacuum sealing, standing, formation, sorting, and secondary sealing.

[0161] In the formula, D / C2 is 2.73.

[0162] Example 3

[0163] The battery was prepared according to the following method:

[0164] (1) Preparation of positive electrode sheet

[0165] The nickel-cobalt-manganese ternary material (chemical formula LiNi 0.93 Co 0.02 Mn 0.04 Ti 0.01 O2), a positive electrode conductive agent (a mixture of conductive carbon black and carbon nanotubes in a mass ratio of 3:1), and polyvinylidene fluoride are mixed in a mass ratio of 97.6:1.35:1.05 to obtain a positive electrode slurry; aluminum oxide (average particle size D of 5 μm) and polyvinylidene fluoride are mixed in a mass ratio of 95:5 to obtain a coating slurry; the positive electrode slurry is uniformly coated on both sides of the aluminum foil, and then dried; then the coating slurry is coated along the length direction of the aluminum foil and in contact with the positive electrode active coating, and then sequentially subjected to drying, rolling, and cutting to obtain a positive electrode sheet.

[0166] The average thickness of the coating is 20 μm, and the size of the coating along the width direction of the positive electrode sheet is 0.2 mm.

[0167] The outer surface of the nickel-cobalt-manganese ternary material has a coating layer, and the coating layer comprises element Zr; the thickness of the coating layer is 25 nm.

[0168] The nickel-cobalt-manganese ternary material is a single crystal particle.

[0169] The number of positive electrode tabs is greater than or equal to 2.

[0170] (2) Preparation of negative electrode sheet

[0171] The negative electrode active material (a mixture of artificial graphite and silicon carbon in a mass ratio of 3:1), conductive carbon black, butadiene rubber, and sodium carboxymethyl cellulose are mixed in a mass ratio of 95:2:1.5:1.5, and then deionized water is added to form a uniform negative electrode slurry; the negative electrode slurry is coated on both sides of the copper foil, and then subjected to drying, rolling, and cutting to obtain a negative electrode sheet.

[0172] The silicon carbon contains Ca element, and the mass content of the Ca element in the silicon carbon accounts for 274 ppm.

[0173] The number of negative electrode tabs is greater than or equal to 2.

[0174] (3) Preparation of electrolyte

[0175] In a glove box (H2O < 0.01 ppm, O2 < 0.01 ppm, Ar atmosphere), PC, EC and DFEA were mixed uniformly in propyl propionate (PP), and then a first lithium salt (LiFSI), a second lithium salt (LiPO2F2) and a third lithium salt (LiPF6) were added thereto, and then PS, TPP and 4% FEC based on the total mass of the electrolyte were added and stirred uniformly, and after passing the moisture and free acid detection, an electrolyte was obtained;

[0176] In the formula, C11 is 17.4%, C12 is 2.1%, C1 is 19.5%; C2 is 60%, C3 is 1.1%, C4 is 2.05%, C5 is 12%, C6 is 0.82%, and C7 is 0.1%.

[0177] (4) Preparation of the separator

[0178] Melamine cyanurate, butadiene styrene rubber and lithium polyacrylate were mixed uniformly according to a mass ratio of 96:2:2, and NMP was added to obtain a functional layer slurry; the functional layer slurry was coated on one side surface of a polyethylene film, and dried to obtain a functional layer; a glue layer (including PVDF and PMMA, wherein the mass ratio of PVDF to PMMA is 1:2, and the solvent is deionized water) was coated on the outer surface of the functional layer and the other side surface of the polyethylene film to obtain a separator;

[0179] In the formula, the average particle size of PVDF is 3 μm;

[0180] The coverage of the glue layer on the outer surface of the separator is 69%;

[0181] The thickness of the glue layer is 4.3 μm, and the thickness of the functional layer is 0.8 μm.

[0182] (5) Preparation of the battery

[0183] The negative electrode sheet prepared in step (2), the positive electrode sheet prepared in step (1) and the separator (polyethylene film) were stacked according to a predetermined procedure to form a core, the core was loaded into an aluminum plastic film shell, and then a PET film was attached outside the aluminum plastic film shell, the electrolyte prepared in step (3) was injected, and then the procedures of vacuum sealing, standing, formation, sorting, two-sealing and the like were performed to prepare a battery;

[0184] In the formula, D / C2 is 8.33.

[0185] Example 4 group

[0186] This group of examples is used to verify the influence of the change of "the mass content ratio C11 of propylene carbonate in the electrolyte".

[0187] This group of examples is carried out with reference to Example 1, except that C11 is changed, and the details are as follows:

[0188] Example 4a, C11 is 3.1%;

[0189] Example 4b, C11 is 24.9%.

[0190] Example 5

[0191] To verify the impact of the change of "the mass content ratio C2 of ethyl fluoroacetate in electrolyte".

[0192] Refer to Example 1, except that DFEA is replaced by the same mass of ethyl 2,2-difluoroacetate.

[0193] Example 6 group

[0194] The examples in this group are used to verify the impact of the change of "the mass content ratio C2 of ethyl fluoroacetate in electrolyte".

[0195] The examples in this group refer to Example 2, except that C2 is changed, specifically as follows:

[0196] Example 6a, C2 is 25.1%; wherein D / C2 is 3.19;

[0197] Example 6b, C2 is 65%; wherein D / C2 is 1.23;

[0198] Example 6c, C2 is 20.2%; wherein D / C2 is 3.96.

[0199] Example 7

[0200] To verify the impact of the change of "the average thickness of the coating".

[0201] Refer to Example 1, except that the average thickness of the coating is changed, specifically, the average thickness of the coating is 3 μm.

[0202] Example 8 group

[0203] The examples in this group are used to verify the impact of the change of "the size of the coating along the width direction of the positive plate".

[0204] The examples in this group refer to Example 1, except that the size of the coating along the width direction of the positive plate is changed, specifically as follows:

[0205] Example 8a, the size of the coating along the width direction of the positive plate is 0.1 mm;

[0206] Example 8b, the size of the coating along the width direction of the positive plate is 10 mm.

[0207] Example 9 group

[0208] This group of examples is used to verify the impact of the change of "D / C2".

[0209] This group of examples is carried out according to examples 2 and 3 respectively, except that D / C2 is regulated by changing C2, as follows:

[0210] Example 9a is carried out according to example 3, except that the electrolyte used in example 2, and D / C2 is 17.06.

[0211] Example 9b is carried out according to example 2, except that the electrolyte used in example 3, and D / C2 is 1.33.

[0212] Example 10 group

[0213] This group of examples is used to verify the impact of the change of "x in the chemical formula of the nickel-cobalt-manganese ternary material".

[0214] This group of examples is carried out according to example 1, except that x is regulated by changing the nickel-cobalt-manganese ternary material, as follows:

[0215] Example 10a, the chemical formula of the nickel-cobalt-manganese ternary material is LiNi 0.8 Co 0.08 Mn 0.08 Mg 0.04 O2, that is, x is 0.8.

[0216] Example 10b, the chemical formula of the nickel-cobalt-manganese ternary material is LiNi 0.95 Co 0.02 Mn 0.02 Mg 0.01 O2, that is, x is 0.95.

[0217] Example 11 group

[0218] This group of examples is used to verify the impact of the change of "the thickness of the coating layer".

[0219] This group of examples is carried out according to example 1, except that the thickness of the coating layer is changed, as follows:

[0220] Example 11a, the thickness of the coating layer is 1 nm.

[0221] Example 11b, the thickness of the coating layer is 40 nm.

[0222] Example 12

[0223] To verify the impact of "whether the nickel-cobalt-manganese ternary material includes polycrystalline particles".

[0224] The same as in Example 1 except that the nickel-cobalt-manganese ternary material comprises single-crystal particles and polycrystal particles, and the mass ratio of the two is 8:2, and the average particle size of the polycrystal particles is 12 μm.

[0225] Example 13 group

[0226] The examples in this group are used to verify the influence of the change of the "positive electrode active material".

[0227] The examples in this group are respectively performed according to Examples 1, 2 and 3 except that the positive electrode active material is changed, and the details are as follows:

[0228] Example 13a, performed according to Example 1 except that the positive electrode active material is a nickel-cobalt-manganese ternary material and lithium iron phosphate in a mass ratio of 85:15; wherein the lithium iron phosphate contains element Al and is a single-crystal particle;

[0229] Example 13b, performed according to Example 2 except that the positive electrode active material is a nickel-cobalt-manganese ternary material and lithium iron phosphate in a mass ratio of 85:15; wherein the lithium iron phosphate contains element Mg and is a single-crystal particle;

[0230] Example 13c, performed according to Example 3 except that the positive electrode active material is a nickel-cobalt-manganese ternary material and lithium iron phosphate in a mass ratio of 85:15; wherein the lithium iron phosphate contains element Mn and is a single-crystal particle;

[0231] In the examples, the lithium iron phosphate satisfies: the average particle size is 0.1 μm-2 μm, the median particle size Dv50 is 0.1 μm-2 μm, and the particle size Dv90 is ≤2.5 μm.

[0232] Example 14 group

[0233] The examples in this group are used to verify the influence of the change of "the mass content ratio C3 of the first lithium salt in the electrolyte".

[0234] The examples in this group are performed according to Example 1 except that C3 is changed, and the details are as follows:

[0235] Example 14a, C3 is 0%, i.e. no first lithium salt is added in the electrolyte;

[0236] Example 14b, C3 is 0.5%;

[0237] Example 14c, C3 is 12.3%.

[0238] Example 15

[0239] Used to verify the influence of "no second lithium salt is added in the electrolyte".

[0240] Refer to Example 1, except that no second lithium salt is added to the electrolyte.

[0241] Example 16

[0242] To verify the effect of "no 1,3-propane sultone is added to the electrolyte".

[0243] Refer to Example 1, except that no 1,3-propane sultone is added to the electrolyte.

[0244] Example 17 group

[0245] The examples in this group are used to verify the effect of the change of "the mass content ratio C7 of tripropargyl phosphate in the electrolyte".

[0246] The examples in this group refer to Example 1, except that C7 is changed, as follows:

[0247] Example 17a, C7 is 0%, that is, no tripropargyl phosphate is added to the electrolyte;

[0248] Example 17b, C7 is 0.01%;

[0249] Example 17c, C7 is 1.99%.

[0250] Example 18

[0251] To verify the effect of the change of "the number of positive electrode tabs and the number of negative electrode tabs".

[0252] Refer to Example 1, except that the number of positive electrode tabs and the number of negative electrode tabs are both 1.

[0253] Example 19 group

[0254] The examples in this group are used to verify the effect of the change of "the mass content ratio of Ca element in the silicon-based material".

[0255] The examples in this group refer to Example 1, except that the mass content ratio of Ca element in the silicon-carbon is changed, as follows:

[0256] Example 19a, the mass content ratio of Ca element in the silicon-carbon is 483ppm;

[0257] Example 19b, the mass content ratio of Ca element in the silicon-carbon is 0ppm.

[0258] Example 20 group

[0259] The examples in this group are used to verify the effect of the change of "the mass content ratio of Ca element in the silicon-carbon". ​

[0260] The present example is performed according to Example 1, except that ethylene carbonate is added to the electrolyte, and C12 is 5%. The specific process is as follows:

[0261] Example 20a, the mass content ratio is 1.5%;

[0262] Example 20b, the mass content ratio is 0.1%;

[0263] Example 20c, the mass content ratio is 3%.

[0264] Example 21

[0265] The effect of changing the mass content ratio of ethylene carbonate in the electrolyte is verified.

[0266] The present example is performed according to Example 1, except that ethylene carbonate is added to the electrolyte, and C12 is 5%.

[0267] The above examples all meet:

[0268] The average particle size of the nickel-cobalt-manganese ternary material is 0.5 μm-15 μm;

[0269] The mass content ratio of silicon in the silicon-carbon is 35%-75%, the silicon-carbon includes a porous carbon matrix and silicon particles in the pore channels of the porous carbon matrix, the average particle size is 5 μm-15 μm, the specific surface area is 1.5 m 2 / g-3m 2 / g, and the sphericity is 0.8-0.99;

[0270] The thickness of the positive electrode tab is 0.1 mm-0.3 mm, the width is 5 mm-10 mm, and the length is 10 mm-50 mm; the thickness of the negative electrode tab is 0.1 mm-0.3 mm, the width is 5 mm-10 mm, and the length is 10 mm-50 mm.

[0271] Comparative Example 1

[0272] The present example is performed according to Example 1, except that the positive electrode sheet is not provided with a coating.

[0273] Comparative Example 2

[0274] The present example is performed according to Example 1, except that PC is replaced by PP with the same mass.

[0275] Comparative Example 3

[0276] The present example is performed according to Example 1, except that the mass content ratio C11 of propylene carbonate in the electrolyte is changed, specifically, C11 is 27%.

[0277] Comparative Example 4

[0278] Example 1 was followed, except that the mass content ratio of ethylene carbonate in the electrolyte was changed to C12, specifically, C12 was 12%.

[0279] Comparative Example 5

[0280] Example 1 was followed, except that DFEA was replaced with ethyl acetate of the same mass.

[0281] Comparative Example 6

[0282] Example 1 was followed, except that the mass content ratio of ethylene fluoride acetate in the electrolyte was changed to C2, specifically, C2 was 15.3%.

[0283] Test Example

[0284] (1) Short circuit test

[0285] The batteries prepared in the examples and comparative examples were subjected to short circuit test, and the specific test method was as follows:

[0286] The battery was placed for 10 min, 0.2C was discharged to 3V, and was placed for 10 min; 0.5C was charged to full capacity, and the cutoff was 0.05C, and was placed for 10 min; it was placed in an environment of 25℃±5℃ for 30 min, and the positive and negative electrodes were short-circuited, and the short-circuit resistance was ≤50mΩ, if the battery did not catch fire and explode, it represented that the test passed; 20 groups of tests were performed for each example and comparative example, and the test results were recorded in Table 1, wherein 20 / 20 represented that 20 groups of tests were performed, and all the 20 groups passed the test; 10 / 20 represented that 20 groups of tests were performed, and all the 10 groups passed the test; and so on.

[0287] (2) High temperature cycle test

[0288] The batteries prepared in the examples and comparative examples were subjected to high temperature cycle test, and the specific test method was as follows:

[0289] The battery was placed in an environment of 45℃±3℃ for 30 min, and the initial thickness was measured and recorded as d1 (thickness under 50% SOC state); two temperature sensing lines were attached on the surface of the battery, and then the battery was completely wrapped with a layer of foam with a thickness of 1cm, 0.5C was discharged to 2.0V at 45℃, and was placed for 30 min; 2C constant current was charged to 4.3V, and the cutoff current was 0.05C, and was placed for 30 min; 3C was discharged to 2.0V, and was placed for 30 min, if the temperature of the battery exceeded 73℃, it was converted to 1C discharge; such cycle was repeated for 300 times, the thickness under full charge state was tested every 50 cycles, the thickness under full charge state was tested after 300 cycles, and was recorded as d2, and the thickness expansion rate was (d2-d1) / d1×100%, and the results were recorded in Table 1.

[0290] (3) Low-temperature discharge test

[0291] The batteries prepared from the examples and the comparative examples were subjected to low-temperature discharge test, and the specific test method was as follows:

[0292] The battery was placed in an environment of 0℃±2℃ for 30 min, discharged to 2.0V at 0.1C, and placed for 30 min; charged to 4.3V at 0.2C constant current, with a cutoff current of 0.05C, and placed for 30 min; discharged to 2.0V at 2C, and placed for 30 min; the capacity at this time was q1, and after 100 cycles, the capacity of the last cycle was recorded as q2, and the capacity retention rate was (q2-q1) / q1×100%; the battery after 100 cycles was disassembled, and whether lithium precipitation occurred in the negative plate was observed; if no lithium precipitation occurred in the negative plate, it was recorded as “no lithium precipitation”, if lithium precipitation occurred at the edge of the negative plate, it was recorded as “slight lithium precipitation”, and if lithium precipitation occurred at the edge and the middle of the negative plate, it was recorded as “lithium precipitation”, and the results were recorded in Table 1.

[0293] Table 1

[0294]

[0295]

[0296]

[0297] From Table 1, it can be seen that the battery of the present application can improve the problem of lithium precipitation under low-temperature discharge compared with the comparative examples, and has good short-circuit safety performance and low high-temperature gas production.

[0298] The preferred embodiments of the present application are described in detail above, but the present application is not limited thereto. Within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be considered as disclosed by the present application, and all fall within the protection scope of the present application.

Claims

1. A battery, characterized by, The positive electrode sheet and the electrolyte are included. The positive electrode sheet includes a positive electrode current collector and a coating layer located at the surface edge of the positive electrode current collector along the length direction; the coating layer includes filler particles, the filler particles include at least one of inorganic particles and nitrogen-containing particles; the inorganic particles include at least one of bormite, aluminum oxide and magnesium oxide, and the nitrogen-containing particles include at least one of melamine, melamine cyanurate, melamine polyphosphate, melamine trithiocyanate and melamine formaldehyde resin; The electrolyte includes non-fluorinated cyclic carbonate and fluorinated ethyl acetate; the non-fluorinated cyclic carbonate includes propylene carbonate and optional ethylene carbonate; the content ratio C1 of the non-fluorinated cyclic carbonate is less than or equal to 25% based on the total mass of the electrolyte, the content ratio C11 of propylene carbonate is 3.1%-24.9%, the content ratio C12 of ethylene carbonate is 0%-5%, and the content ratio C2 of the fluorinated ethyl acetate is 20.2%-70%.

2. The battery of claim 1, wherein, The fluorinated ethyl acetate includes 2,2-difluoroethyl acetate and / or ethyl 2,2-difluoroacetate; preferably, the fluorinated ethyl acetate includes 2,2-difluoroethyl acetate; And / or, C1 is less than or equal to 20.1%; And / or, C11 is 5.1%-17.4%; And / or, C2 is 25.1%-65%; preferably, 29.3%-60%.

3. The battery according to claim 1 or 2, wherein The average thickness of the coating layer is 3-20μm; preferably, 5-20μm; And / or, the size of the coating layer along the width direction of the positive electrode sheet is 0.1-10mm; preferably, 0.2-5mm; And / or, the average particle size D of the filler particles is 0.05-5μm; preferably, 0.1-3μm; Preferably, D (unit: μm) and C1 satisfy 1≤D / C2≤18; more preferably, 2.5≤D / C2≤8.

5.

4. The battery according to claim 1 or 2, wherein The electrolyte further includes a first lithium salt, the first lithium salt includes lithium bisfluorosulfonylimide and / or lithium bistrifluoromethylsulfonylimide; preferably, the content ratio C3 of the first lithium salt is 0.5%-12.3% based on the total mass of the electrolyte; more preferably, C3 is 1.1%-9.5%; And / or, the electrolyte further includes a second lithium salt, the second lithium salt includes lithium difluorophosphate; preferably, the content ratio C4 of the second lithium salt is 0.01%-2.05% based on the total mass of the electrolyte; And / or, the electrolyte further includes a third lithium salt, the third lithium salt includes lithium hexafluorophosphate; preferably, the content ratio C5 of the third lithium salt is 6%-18% based on the total mass of the electrolyte.

5. The battery of claim 1 or 2, wherein, The electrolyte further includes 1,3-propane sultone; preferably, the content ratio C6 of 1,3-propane sultone is 0.82%-5.68% based on the total mass of the electrolyte; And / or, the electrolyte further comprises tripropargyl phosphate; preferably, a content ratio C7 of tripropargyl phosphate is 0.01%-1.99% based on a total mass of the electrolyte; more preferably, C7 is 0.1%-0.9%.

6. The battery of claim 1 or 2, wherein, The positive electrode sheet further comprises a positive electrode active coating layer, the positive electrode active coating layer is arranged adjacent to the coating layer; the positive electrode active coating layer comprises a positive electrode active material; the positive electrode active material comprises a nickel-cobalt-manganese ternary material and / or a lithium iron phosphate.

7. The battery of claim 6, wherein, The chemical formula of the nickel-cobalt-manganese ternary material is LiNi x Co y Mn z M a O2, wherein 0.8≤x≤0.95, 0.01≤y≤0.2, 0.01≤z≤0.18, 0<a≤0.1, and M includes at least one of Al, Mg, Y, W, B, Zr, Ti, Sr, La, and Nb. Preferably, the outer surface of the nickel-cobalt-manganese ternary material has a coating layer, and the thickness of the coating layer is 1-40 nm; more preferably, 2-25 nm; Preferably, 0.85≤x≤0.93; Preferably, the nickel-cobalt-manganese ternary material comprises single crystal particles and / or polycrystal particles; more preferably, the single crystal particles; Preferably, the average particle size of the nickel-cobalt-manganese ternary material is 0.5-15 μm.

8. The battery of claim 6, wherein, The lithium iron phosphate contains at least one of elements Ti, Al, Mg, Co, Zr, Mn, Sr, La and Nb; Preferably, the lithium iron phosphate comprises single crystals; Preferably, the average particle size of the lithium iron phosphate is 0.1-2 μm.

9. The battery of claim 1 or 2, wherein, The battery further comprises a negative electrode sheet; the negative electrode sheet comprises a negative electrode current collector and a negative electrode active coating layer located on at least one side surface of the negative electrode current collector, the negative electrode active coating layer comprises a negative electrode active material, and the negative electrode active material comprises a silicon-based material; Preferably, the sphericity of the silicon-based material is 0.8-0.99; Preferably, the silicon-based material contains Ca element; more preferably, the content ratio of Ca element is 10-500 ppm based on the total mass of the silicon-based material; Preferably, the silicon-based material comprises at least one of silicon element, silicon-oxygen, silicon-carbon and silicon alloy; More preferably, the silicon-based material comprises the silicon-carbon; More preferably, the mass content ratio of silicon element in the silicon-carbon is 35%-75%; More preferably, the silicon-carbon comprises a porous carbon matrix and silicon particles in the pore channels of the porous carbon matrix; More preferably, the average particle size of the silicon-carbon is 5-15 μm; More preferably, the specific surface area of the silicon-carbon is 1.5 m 2 / g-3m 2 / g.

10. The battery of claim 1 or 2, wherein, The positive electrode sheet further comprises a positive electrode tab; the battery further comprises a negative electrode sheet, and the negative electrode sheet comprises a negative electrode tab; Preferably, the number of the positive electrode tabs is greater than or equal to 2; Preferably, the number of the negative electrode tabs is greater than or equal to 2.

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