Battery cell and electrochemical device comprising same

Abstract

The invention relates to the field of battery materials, in particular to a battery cell and an electrochemical device comprising the battery cell, the battery cell comprises a positive pole piece, a negative pole piece, electrolyte and a diaphragm located between the positive pole piece and the negative pole piece; the single-crystal nickel-cobalt-manganese ternary positive electrode material and the polycrystal nickel-cobalt-manganese ternary positive electrode material are used in a combined manner; the width A1 of the first heat-resistant strip layer and the interval width A2 are mutually correlated; due to the strict control of the mutual relation between the ratio C of the two positive electrode materials and the width A1 and the interval width A2 of the first heat-resistant strip layer and the strict control of the thickness difference between the first heat-resistant strip layer and the second heat-resistant strip layer, the cycling stability of a battery system of the ternary positive electrode material is remarkably improved on the basis of maintaining relatively high heat safety; and the battery can still have high cycle performance and excellent rate capability in a high-rate rapid charging and discharging scene.

Description

Technical Field

[0001] The present application relates to the field of battery materials, and particularly to an electric core and an electrochemical device including the electric core. Background Art

[0002] Lithium-ion batteries are widely used in many fields such as 3C consumer products and electric vehicles. In the increasingly competitive market environment, battery technology is continuously moving towards larger capacity and higher charging power, especially ternary lithium-ion batteries.

[0003] Nickel-cobalt-manganese ternary cathode material (chemical formula Li(Ni x Co y Mn 1-x-y )O2, abbreviated as NCM), due to its excellent high energy density characteristics, has been extremely widely used in many key fields such as electric vehicles, mobile devices, and energy storage systems. However, the capacity attenuation rate of the electric core made of nickel-cobalt-manganese ternary cathode material is relatively fast, and frequent charge and discharge cycles will accelerate the attenuation of the battery capacity. Especially in the scenario of high-rate fast charge and discharge, the high-nickel ternary cathode material is extremely prone to cation mixing and microcracks caused by lattice stress, which makes the internal structure of the battery become more fragile, and the problem of cycle stability needs to be solved urgently, which has become the key bottleneck restricting its further development. Summary of the Invention

[0004] The present application provides an electric core and an electrochemical device including the electric core, aiming to solve to a certain extent the problem that the existing lithium-ion battery has poor cycle stability, resulting in rapid capacity attenuation under frequent charge and discharge cycles, especially under high-rate fast charge and discharge conditions.

[0005] In a first aspect, the present application provides an electric core, including a positive electrode plate, a negative electrode plate, an electrolyte, and a separator located between the positive electrode plate and the negative electrode plate. The separator includes a base film and a heat-resistant layer located on at least one surface of the base film. The heat-resistant layer includes a plurality of first heat-resistant strip layers spaced apart from each other and a second heat-resistant strip layer disposed between two adjacent first heat-resistant strip layers. The thickness H1 of the first heat-resistant strip layer and the thickness H2 of the second heat-resistant strip layer satisfy: 0μm < H1 - H2 ≤ H1, where the units of H1 and H2 are both μm;

[0006] The positive electrode plate includes a current collector and a positive electrode active material layer disposed on at least one surface of the current collector. The positive electrode active material layer includes a positive electrode active material, and the positive electrode active material includes a single crystal nickel-cobalt-manganese ternary cathode material and a polycrystal nickel-cobalt-manganese ternary cathode material;

[0007] The width A1 of the first heat-resistant strip layer, the spacing width A2 between two adjacent first heat-resistant strip layers, and the weight ratio C of the single-crystalline nickel cobalt manganese ternary cathode material to the polycrystalline nickel cobalt manganese ternary cathode material in the cathode active material layer satisfy the following relationship: 2.5 ≤ (A1 / A2) × C ≤ 20; where the units of A1 and A2 are both μm.

[0008] In an alternative embodiment, the distance D mm between the edges of the negative electrode tab and the positive electrode tab on the same side in the width direction of the battery cell and the tab edge distance L mm satisfy the following relationship: 10 ≤ D × L ≤ 100; where D is 0.1 to 3 and L is 6 to 50.

[0009] In an alternative embodiment, 4.5 ≤ (A1 / A2) × C ≤ 15; and / or, 1 μm ≤ H1 - H2 ≤ 5 μm.

[0010] In an alternative embodiment, A1 is 30 μm - 100 μm; and / or, A2 is 6.7 μm - 20 μm; and / or, 1.5 ≤ A1 / A2 ≤ 4.5; and / or, C is 1 - 4; and / or, 0.5 μm ≤ H1 ≤ 10 μm; and / or, 0.5 μm ≤ H2 ≤ 8 μm.

[0011] In an alternative embodiment, the battery cell satisfies one or more of the following conditions:

[0012] A. The first heat-resistant strip layer includes first heat-resistant particles;

[0013] B. The second heat-resistant strip layer includes second heat-resistant particles;

[0014] C. The separator further includes an adhesive layer, and the adhesive layer is located on the surface of the base film and / or the heat-resistant layer.

[0015] In an alternative embodiment, the battery cell satisfies one or more of the following conditions:

[0016] A. The particle size Dv50 of the first heat-resistant particles is 0.1 μm to 2.5 μm;

[0017] B. The composition of the first heat-resistant particles includes at least one of boehmite (γ-AlOOH), alumina (Al2O3), barium sulfate (BaSO4), magnesia (MgO), magnesium hydroxide (Mg(OH)2), silica (SiO2), tin dioxide (SnO2), titanium dioxide (TiO2), calcium oxide (CaO), zinc oxide (ZnO), zirconium oxide (ZrO2), yttrium oxide (Y2O3), nickel oxide (NiO), cerium oxide (CeO2), strontium titanate (SrTiO3), barium titanate (BaTiO3), magnesium fluoride (MgF2), melamine cyanurate, melamine polyphosphate, melamine trithiocyanate, aluminum diethylphosphite, pentaerythritol, and triazine charring agent;

[0018] C. Based on the total mass of the first heat-resistant strip layer, the first heat-resistant strip layer includes 40wt% - 96wt% of the first heat-resistant particles, 3wt% - 59.3wt% of the binder, and 0.7wt% - 3wt% of the dispersant;

[0019] D. The particle size Dv50 of the second heat-resistant particles is 0.1μm - 2.5μm;

[0020] E. The composition of the second heat-resistant particles includes at least one of boehmite (γ-AlOOH), alumina (Al2O3), barium sulfate (BaSO4), magnesia (MgO), magnesium hydroxide (Mg(OH)2), silica (SiO2), tin dioxide (SnO2), titanium dioxide (TiO2), calcium oxide (CaO), zinc oxide (ZnO), zirconium oxide (ZrO2), yttrium oxide (Y2O3), nickel oxide (NiO), cerium oxide (CeO2), strontium titanate (SrTiO3), barium titanate (BaTiO3), magnesium fluoride (MgF2), melamine cyanurate, melamine polyphosphate, melamine trithiocyanate, aluminum diethylphosphite, pentaerythritol, and triazine charring agent;

[0021] F. Based on the total mass of the second heat-resistant strip layer, the second heat-resistant strip layer includes 40wt% - 96wt% of the second heat-resistant particles, 3wt% - 59.3wt% of the binder, and 0.7wt% - 3wt% of the dispersant;

[0022] G. The thickness of the glue coating layer is 0.5 - 3μm;

[0023] H. The glue coating layer includes a polymer.

[0024] In an alternative embodiment, the particle size Dv10 of the single-crystal nickel cobalt manganese ternary cathode material is 0.8μm - 4μm, Dv50 is 1μm - 6μm, and Dv90 is 3μm - 10μm.

[0025] In an alternative embodiment, the BET of the single-crystal nickel cobalt manganese ternary cathode material is 0.5 m 2 / g - 1.4 m 2 / g.

[0026] In an alternative embodiment, the particle size Dv10 of the polycrystalline nickel cobalt manganese ternary cathode material is 3 μm - 13 μm, Dv50 is 6 μm - 15 μm, and Dv90 is 12 μm - 25 μm.

[0027] In an alternative embodiment, the BET of the polycrystalline nickel cobalt manganese ternary cathode material is 0.3 m 2 / g - 1.0 m 2 / g.

[0028] In an alternative embodiment, the molar content of nickel element in the single-crystal nickel cobalt manganese ternary cathode material accounts for 85% - 98% of the total nickel cobalt manganese metal elements.

[0029] In an alternative embodiment, the molar content of nickel element in the polycrystalline nickel cobalt manganese ternary cathode material accounts for 80% - 95% of the total nickel cobalt manganese metal elements.

[0030] In an alternative embodiment, the molar content of cobalt element in the single-crystal nickel cobalt manganese ternary cathode material accounts for 1% - 14% of the total nickel cobalt manganese metal elements.

[0031] In an alternative embodiment, the molar content of cobalt element in the polycrystalline nickel cobalt manganese ternary cathode material accounts for 1% - 19% of the total nickel cobalt manganese metal elements.

[0032] In an alternative embodiment, the molar content of manganese element in the single-crystal nickel cobalt manganese ternary cathode material accounts for 1% - 10% of the total nickel cobalt manganese metal elements.

[0033] In an alternative embodiment, the molar content of manganese element in the polycrystalline nickel cobalt manganese ternary cathode material accounts for 1% - 10% of the total nickel cobalt manganese metal elements.

[0034] In an alternative embodiment, in the single-crystal nickel cobalt manganese ternary cathode material, the molar content of nickel element accounts for 90% - 95% of the total nickel cobalt manganese metal elements.

[0035] In an alternative embodiment, the molar content of nickel element in the polycrystalline nickel cobalt manganese ternary cathode material accounts for 87% - 92% of the total nickel cobalt manganese metal elements.

[0036] In an alternative embodiment, the molar content of cobalt element in the single-crystal nickel cobalt manganese ternary cathode material accounts for 2% - 10% of the total nickel cobalt manganese metal elements.

[0037] In an alternative embodiment, the molar content of cobalt element in the polycrystalline nickel cobalt manganese ternary cathode material accounts for 2%-10% of the total metal elements of nickel, cobalt and manganese.

[0038] In an alternative embodiment, the molar content of manganese element in the single crystal nickel cobalt manganese ternary cathode material accounts for 2%-7% of the total metal elements of nickel, cobalt and manganese.

[0039] In an alternative embodiment, the molar content of manganese element in the polycrystalline nickel cobalt manganese ternary cathode material accounts for 2%-7% of the total metal elements of nickel, cobalt and manganese.

[0040] The technical solution of this application has the following advantages:

[0041] The battery cell provided by the present application includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator located between the positive electrode sheet and the negative electrode sheet. The separator includes a base film and a heat-resistant layer located on at least one surface of the base film. The heat-resistant layer includes a plurality of first heat-resistant strip layers arranged at intervals and a second heat-resistant strip layer arranged between two adjacent first heat-resistant strip layers. The thickness H1 of the first heat-resistant strip layer and the thickness H2 of the second heat-resistant strip layer satisfy: 0μm < H1 - H2 ≤ H1, where the units of H1 and H2 are both μm. The positive electrode sheet includes a current collector and a positive electrode active material layer provided on at least one surface of the current collector. The positive electrode active material layer includes a positive electrode active material, and the positive electrode active material includes a single-crystalline nickel cobalt manganese ternary positive electrode material and a polycrystalline nickel cobalt manganese ternary positive electrode material. The width A1 of the first heat-resistant strip layer, the interval width A2 between two adjacent first heat-resistant strip layers, and the weight ratio C of the single-crystalline nickel cobalt manganese ternary positive electrode material to the polycrystalline nickel cobalt manganese ternary positive electrode material in the positive electrode active material layer satisfy the following relational expression: 2.5 ≤ (A1 / A2) × C ≤ 20; where the units of A1 and A2 are both μm. By controlling the thickness difference between the first heat-resistant strip layer and the second heat-resistant strip layer and ensuring that the relational expression of the width A1 of the first heat-resistant strip layer, the interval width A2, and the ratio C of the two positive electrode active materials satisfies the above range, it is possible to avoid the depression formed by the heat-resistant layer on the base film being too shallow when the thickness difference is too small or (A1 / A2) × C is too large, which may cause the positive electrode active material to be unable to maintain the stability of the interface in the later stage of battery cycle expansion. It can also avoid the depression formed by the heat-resistant layer on the base film being too deep when the thickness difference is too large or (A1 / A2) × C is too small, resulting in a reduction in the rate performance, cycle life, and thermal safety of the battery. In summary, by jointly using the single-crystalline nickel cobalt manganese ternary positive electrode material and the polycrystalline nickel cobalt manganese ternary positive electrode material and strictly controlling the mutual relationship between the width A1 of the first heat-resistant strip layer and the interval width A2, the mutual relationship between the ratio C of the two materials and the width A1 of the first heat-resistant strip layer and the interval width A2, and the thickness difference between the first heat-resistant strip layer and the second heat-resistant strip layer, the cycle stability of the battery system with the ternary positive electrode material is significantly improved on the basis of maintaining high thermal safety, enabling the battery to still achieve high cycle performance and excellent rate performance in the scenario of high-rate fast charging and discharging.

[0042] Additional aspects and advantages of embodiments of the present application will be described and shown in part in the following description, or will be explained through the implementation of embodiments of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] To more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0044] Figure 1 It is a schematic structural diagram of the separator in Example 1;

[0045] Figure 2 It is a schematic structural diagram of the separator in Example 10;

[0046] Figure 3 It is a schematic structural diagram of the separator in Example 15;

[0047] Figure 4 It is a schematic structural diagram of the separator in Example 16;

[0048] Figure 5 It is a schematic structural diagram of the separator in Example 17;

[0049] Reference numerals:

[0050] 1. Base film; 2. First heat-resistant strip layer; 3. Second heat-resistant strip layer; 4. First adhesive coating layer; 5. First adhesive strip layer; 6. Second adhesive strip layer. Specific embodiments

[0051] The following embodiments are provided to better further understand the present application, which is not limited to the best embodiment, and does not limit the content and protection scope of the present application. Any product identical or similar to the present application obtained by anyone under the inspiration of the present application or by combining the features of the present application with those of other prior arts falls within the protection scope of the present application.

[0052] For those embodiments where specific experimental steps or conditions are not indicated, the operations or conditions of the conventional experimental steps described in the literature in this field can be followed. For reagents or instruments without indicating the manufacturer, they are all conventional reagent products that can be obtained through commercial purchase.

[0053] In addition, the technical features involved in different embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0054] The capacity attenuation rate of the battery cell made of nickel-cobalt-manganese ternary cathode material is relatively fast. Frequent charge and discharge cycles will accelerate the attenuation of the battery capacity. Especially in the scenario of fast charge and discharge at high rates, the high-nickel ternary cathode material is extremely prone to cation mixing and microcracks caused by lattice stress, resulting in rapid capacity attenuation. This application provides a battery cell, aiming to solve to a certain extent the problem of rapid capacity attenuation caused by the poor cycle stability of existing lithium-ion batteries during frequent charge and discharge cycles, especially the problem of rapid capacity attenuation during fast charge and discharge at high rates. The technical solution adopted in this application is described as follows.

[0055] In a first aspect, this application provides a battery cell including a positive electrode tab, a negative electrode tab, an electrolyte, and a separator located between the positive electrode tab and the negative electrode tab. The separator includes a base film and a heat-resistant layer located on at least one surface of the base film. The heat-resistant layer includes a plurality of first heat-resistant strip layers spaced apart from each other and a second heat-resistant strip layer disposed between two adjacent first heat-resistant strip layers. The thickness H1 of the first heat-resistant strip layer and the thickness H2 of the second heat-resistant strip layer satisfy: 0μm < H1 - H2 ≤ H1, where the units of H1 and H2 are both μm; the positive electrode tab includes a current collector and a positive electrode active material layer disposed on at least one surface of the current collector. The positive electrode active material layer includes a positive electrode active material, and the positive electrode active material includes a single-crystal nickel-cobalt-manganese ternary cathode material and a polycrystalline nickel-cobalt-manganese ternary cathode material; the width A1 of the first heat-resistant strip layer, the spacing width A2 between two adjacent first heat-resistant strip layers, and the weight ratio C of the single-crystal nickel-cobalt-manganese ternary cathode material to the polycrystalline nickel-cobalt-manganese ternary cathode material in the positive electrode active material layer satisfy the following relational expression: 2.5 ≤ (A1 / A2) × C ≤ 20; where the units of A1 and A2 are both μm.

[0056] In this application, the setting of the first heat-resistant strip layer significantly improves the heat resistance of the separator and enhances the thermal safety of the battery cell. The thickness control between the first heat-resistant strip layer and the second heat-resistant strip layer creates intervals between adjacent first ceramic strip layers, providing more ion transport channels for the charge and discharge process of the battery, effectively enhancing the migration rate of active ions, thereby improving the charge and discharge efficiency of the battery, effectively improving the available discharge depth of the battery, reducing the minimum remaining charge (SOC) level at which the battery can effectively supply power, increasing the performance and reliability of the battery under high-rate working conditions, and enhancing the cycle service life of the battery system using ternary cathode materials. A second heat-resistant strip layer may or may not be provided between two adjacent first heat-resistant strip layers. When a second heat-resistant strip layer is provided between two adjacent first heat-resistant strip layers, it can not only further improve the heat resistance of the separator, thus significantly enhancing the thermal safety of the battery, but also provide more ion transport channels for the charge and discharge process of the battery by controlling the thickness of the second heat-resistant strip layer to be less than that of the first heat-resistant strip layer, effectively enhancing the migration rate of active ions, and enhancing the cycle service life of the battery system using ternary cathode materials.

[0057] The cathode active materials on the cathode active material layer include single-crystal nickel cobalt manganese ternary cathode materials and polycrystalline nickel cobalt manganese ternary cathode materials. Single-crystal nickel cobalt manganese ternary cathode materials have excellent structural stability and cycle performance, especially good cycle performance under high voltage and high temperature conditions, but have poor specific capacity and rate performance. Polycrystalline nickel cobalt manganese ternary cathode materials are prone to lattice rupture during the charge and discharge cycle process, with poor cycle performance, but better performance in terms of specific capacity and rate performance. The combined use of single-crystal nickel cobalt manganese ternary cathode materials and polycrystalline nickel cobalt manganese ternary cathode materials in a reasonable ratio can integrate the advantages of both to meet different battery performance requirements. However, during the battery cycle process, the polycrystalline ternary is prone to lattice rupture, resulting in a short time for high-rate discharge under low SOC conditions, thus leading to a short cycle life of the battery cell under high-rate charge and discharge conditions.

[0058] By using single-crystal nickel cobalt manganese ternary cathode material and polycrystalline nickel cobalt manganese ternary cathode material in combination, and through strict control of the mutual relationship between the width A1 of the first heat-resistant strip layer and the interval width A2, the mutual relationship between the ratio C of the two materials and the width A1 of the first heat-resistant strip layer and the interval width A2, as well as strict control of the thickness difference between the first heat-resistant strip layer and the second heat-resistant strip layer, the cycle stability of the battery system of the ternary cathode material is significantly improved on the basis of maintaining high thermal safety, enabling the battery to still balance high cycle performance and excellent rate performance in the scenario of fast charge and discharge at high rates. Specifically, by controlling the thickness difference between the first heat-resistant strip layer and the second heat-resistant strip layer to satisfy the range of 0μm < H1 - H2 ≤ H1, it can be avoided that when the thickness difference is too small, the depression formed by the heat-resistant layer on the base film is too shallow, the electrolyte storage is reduced, and the optimization of the electrolyte infiltration on the electrode sheet cannot be achieved, resulting in insufficient electrolyte infiltration of the single-crystal nickel cobalt manganese ternary cathode material and the polycrystalline nickel cobalt manganese ternary cathode material in the electrode sheet, and the formed interfacial film is too thin to maintain the rapid capacity decay under the conditions of fast charge and discharge at high rates of the battery, thus shortening the cycle life of the battery. It can also be avoided that when the thickness difference is too large, the depression formed by the heat-resistant layer on the base film is too deep. On the one hand, it exacerbates the uneven charge distribution on the electrode surface, reduces the lithium ion insertion and extraction speed, and thus reduces the rate performance of the battery; on the other hand, the continuity of the heat-resistant layer is reduced, the bonding force between the separator and the electrode sheet is weakened, the stress at the contact interface between the separator and the electrode sheet is too concentrated, deteriorating the interface problem, and easily causing the problem of lithium deposition, thus shortening the cycle life of the battery. In addition, the decrease in the coating amount of the ceramic material leads to a decrease in the thermal safety of the separator.

[0059] By controlling the battery cell to meet the condition of the relational expression 2.5 ≤ A1 / A2 × C ≤ 20, not only can the electrolyte content between the interfaces be made appropriate, a CEI film with a uniform thickness be formed, the interface impedance be reduced, the interface performance between the separator and the positive electrode be improved, the problem that grain boundary cracks are likely to occur in polycrystalline ternary materials during charge and discharge be improved, the structural stability of the ternary positive electrode material be enhanced, and the capacity decay of the ternary positive electrode material be slowed down. Moreover, the rate performance of the battery can be effectively improved, the minimum remaining power (SOC) level at which the battery can effectively supply power be reduced, the available discharge depth of the battery be improved, and excellent cycle performance be exhibited at the same time. The relational expression A1 / A2 × C should not be too large. If it exceeds 20, the storage amount of the electrolyte will decrease due to the too wide first heat-resistant strip layer, resulting in a reduction in the contact area between the free electrolyte and the positive electrode material and / or a longer lithium-ion diffusion path due to the excessive proportion of the single-crystal nickel cobalt manganese ternary positive electrode material. The combined effect leads to a reduction in the rate performance of the battery cell, and the cycle life of the battery is shortened under high-rate charge and discharge conditions. The relational expression A1 / A2 × C should not be too small. If it is less than 2.5, the excessive electrolyte storage caused by the too small width of the first heat-resistant strip layer reacts with the highly active surface (especially the grain boundaries after rupture) of the excessive nickel cobalt manganese ternary positive electrode material, generating more gases (such as CO2, CH4) and a thick and unstable CEI film (positive electrode electrolyte interface film), resulting in an increase in internal resistance and capacity decay. In addition, on the one hand, the thermal safety of the separator will decrease due to the too wide second heat-resistant strip layer, or the side reactions will increase due to the relatively high proportion of the polycrystalline nickel cobalt manganese ternary positive electrode material, the risk of gas production will increase or the gas production amount will increase, and the internal pressure difference will be too large, resulting in an increased risk of short circuit of the electrode sheet, which will also lead to a decrease in the thermal safety of the battery. For example, H1 - H2 is 0.1 μm, 0.5 μm, 2 μm, 5 μm, 10 μm, H1 or within the range composed of any two of the above values. Among them, when "H1 - H2 = H1", it means that the second heat-resistant strip layer does not exist. The value of A1 / A2 × C can be 2.5, 4.5, 5, 6, 8, 10, 12, 15, 20 or within the range composed of any two of the above values.

[0060] In an alternative embodiment, the distance D mm between the edges of the negative electrode tab and the positive electrode tab on the same side in the width direction of the battery cell and the tab edge distance L mm satisfy the following relationship: 10 ≤ D × L ≤ 100. By controlling D × L within the range of 10 to 100, the tab edge distance and the size of the negative excess region can be matched. On the one hand, the rate performance of the battery is effectively improved, and at the same time, excellent cycle performance is achieved; on the other hand, the tab distance and the overhang region of the negative electrode can be made appropriate, avoiding unreasonable tab edge distance or overhang design. The BMS may need to increase the minimum SOC (for example, from 5% to 10%) to prevent lithium plating or over-discharge, thereby sacrificing some available capacity to ensure safety. For example, D × L is 10, 20, 50, 60, 80, 100 or within the range composed of any two of the above values.

[0061] When D × L < 10, the tab edge distance or the negative excess region will be too small, resulting in difficult preparation and hard-to-achieve engineering precision. Even if the manufacturing difficulty is overcome, during the charge and discharge process of the battery, the position of the positive electrode tab edge relative to the negative electrode often causes lithium accumulation in the corresponding negative electrode due to high-rate charge and discharge, and lithium intercalation cannot be quickly completed on the negative electrode side. Instead, lithium plating is likely to occur at this edge position, thus shortening the battery life; or it may lead to an increase in the internal resistance of the battery, thereby increasing the voltage drop of the battery, reducing the discharge performance of the battery, increasing energy loss, and shortening the battery life; and too small a tab edge distance may cause too high a local current density, especially at the end of charge and discharge (low SOC), which may trigger the precipitation of lithium ions on the negative electrode surface (lithium plating), resulting in the loss of active lithium and capacity attenuation. This will force the battery management system (BMS) to cut off the discharge in advance to protect the battery, thereby indirectly increasing the minimum SOC value. When D × L > 100, the first efficiency (first charge and discharge efficiency) of the battery will decrease, and the capacity of the battery will also gradually decrease. The tab edge distance or the negative excess region will be too large. The too large overhang region may generate uneven stress during the cyclic expansion / contraction process of the battery, resulting in electrode deformation or delamination; too large a tab edge distance will cause an increase in the transmission distance of the current on the current collector, resulting in an increase in local resistance (especially in the edge region), triggering uneven current distribution. The increase in internal resistance and uneven current distribution will aggravate battery polarization, especially at low SOC (remaining power), which may trigger the voltage cut-off condition in advance, shortening the available capacity range.

[0062] Among them, the negative overhang region (Overhang region) refers to the distance Dmm in the width direction of the battery cell between the edges of the negative electrode tab and the positive electrode tab on the same side in the design of lithium-ion batteries. The increase of this distance will lead to the increase of the Overhang region. As the Overhang region on the width direction of the negative electrode tab increases, the first efficiency (first charge-discharge efficiency) of the battery will decrease, and the capacity of the battery will also gradually decrease. This is because during the charging process, some lithium ions will diffuse into the negative overhang region, resulting in the decrease of the first efficiency and capacity. Therefore, a reasonable Overhang design is crucial for optimizing battery performance and extending battery life. In the present invention, the distance Dmm between the edges of the negative electrode tab and the positive electrode tab on the same side in the width direction of the battery cell is between 0.1 and 3 mm, that is, D is 0.1 to 3. For example, D is 0.1, 0.2, 0.5, 1, 2, 3 or within the range composed of any two of the above values. When the D values on both sides of the negative electrode tab are inconsistent, the minimum value is taken.

[0063] The ear margin is the distance from the ear to the edge of the battery cell. The change of the ear position can significantly affect the internal resistance of the battery. If the ear margin is too small, the distance between the positive and negative ears is too large, which may lead to an increase in the internal resistance of the battery, thereby increasing the voltage drop of the battery and reducing the discharge performance of the battery. Increase energy loss, thereby shortening the service life of the battery. If the ear margin is too large, the distance between the positive and negative ears is too small, which may cause electrode short circuit, trigger the battery cell to catch fire, and may also cause poor heat dissipation and imbalance inside the battery, directly affecting the service life of the battery. In the present invention, the ear margin range is in the range of 6 mm - 50 mm, that is, L is 6 to 50. For example, L is 6, 10, 20, 30, 40, 60 or within the range composed of any two of the above values.

[0064] In an alternative embodiment, A1 is 30 μm - 100 μm; and / or, A2 is 6.7 μm - 20 μm. As an example, A1 can be 30 μm, 50 μm, 80 μm, 100 μm or within the range composed of any two of the above values. As an example, A2 can be 6.7 μm, 8 μm, 10 μm, 15 μm, 20 μm or within the range composed of any two of the above values.

[0065] In an alternative embodiment, when controlling A1 / A2 in the range of 1.5 - 4.5, the spacer region between the first heat-resistant strip layers provides more ion transport channels, effectively improving the migration rate of active ions. For example, the value of A1 / A2 can be 1.5, 1.8, 2, 2.5, 3, 3.5, 4, 4.5 or within the range composed of any two of the above values.

[0066] In an alternative embodiment, 0.5 μm ≤ H1 ≤ 10 μm. With the separator configured in this way, it can not only enhance the affinity with the electrolyte, promote the uniform distribution of the electrolyte, and reduce the interfacial resistance, but also prevent the separator from severely shrinking at high temperatures. For example, the thickness H1 of the first heat-resistant strip layer is 0.5 μm, 2 μm, 5 μm, 10 μm, or within the range formed by any two of the above values. In an alternative embodiment, 0.5 μm ≤ H2 ≤ 8 μm; for example, H2 is 0 μm, 5 μm, 8 μm, or within the range formed by any two of the above values.

[0067] In an alternative embodiment, C is 1 - 4. As an example, C can be 1, 2, 3, 4, or within the range formed by any two of the above values. In this application, the weight ratio C of the single-crystalline nickel cobalt manganese ternary cathode material to the polycrystalline nickel cobalt manganese ternary cathode material in the positive electrode active material layer is controlled to be 1 - 4. That is to say, based on the total mass of the positive electrode active material, the mass proportion of the single-crystalline nickel cobalt manganese ternary cathode material is 50% - 80%, and the mass proportion of the polycrystalline nickel cobalt manganese ternary cathode material is 20% - 50%. For example, the mass proportion of the single-crystalline nickel cobalt manganese ternary cathode material is 50%, 60%, 70%, 80%, or within the range formed by any two of the above values, and the mass proportion of the polycrystalline nickel cobalt manganese ternary cathode material is 20%, 30%, 40%, 50%, or within the range formed by any two of the above values.

[0068] In an alternative embodiment, the first heat-resistant strip layer includes first heat-resistant particles; specifically, the particle size of the first heat-resistant particles is 0.1 μm - 2.5 μm. By controlling the particle size of the first heat-resistant particles within the above range, it is not only beneficial to control the separator with an appropriate porosity range, thereby improving the migration efficiency of lithium ions, but also beneficial to improving the heat resistance of the separator, thereby improving the thermal safety of the battery. For example, the particle size of the first heat-resistant particles is 0.1 μm, 0.5 μm, 1 μm, 2 μm, 2.5 μm, or within the range formed by any two of the above values. For example, the composition of the first heat-resistant particles includes at least one of boehmite (γ - AlOOH), alumina (Al2O3), barium sulfate (BaSO4), magnesium oxide (MgO), magnesium hydroxide (Mg(OH)2), silicon dioxide (SiO2), tin dioxide (SnO2), titanium dioxide (TiO2), calcium oxide (CaO), zinc oxide (ZnO), zirconium oxide (ZrO2), yttrium oxide (Y2O3), nickel oxide (NiO), cerium oxide (CeO2), strontium titanate (SrTiO3), barium titanate (BaTiO3), magnesium fluoride (MgF2), melamine cyanurate, melamine polyphosphate, melamine trithiocyanate, aluminum diethyl phosphite, pentaerythritol, and triazine charring agent.

[0069] In an alternative embodiment, when a second heat-resistant strip layer is disposed between two adjacent first heat-resistant strip layers, the second heat-resistant strip layer includes second heat-resistant particles; specifically, the particle size of the second heat-resistant particles is 0.1 μm to 2.5 μm. By controlling the particle size of the second heat-resistant particles within the above range, it is not only beneficial to control the diaphragm with a suitable porosity range, thereby improving the migration efficiency of lithium ions, but also beneficial to improving the heat resistance of the diaphragm, thereby improving the thermal safety of the battery. Exemplarily, the particle size of the second heat-resistant particles is 0.1 μm, 0.5 μm, 1 μm, 2 μm, 2.5 μm or within the range composed of any two of the above values. Exemplarily, the composition of the second heat-resistant particles includes at least one of boehmite (γ-AlOOH), alumina (Al2O3), barium sulfate (BaSO4), magnesium oxide (MgO), magnesium hydroxide (Mg(OH)2), silicon dioxide (SiO2), tin dioxide (SnO2), titanium dioxide (TiO2), calcium oxide (CaO), zinc oxide (ZnO), zirconium oxide (ZrO2), yttrium oxide (Y2O3), nickel oxide (NiO), cerium oxide (CeO2), strontium titanate (SrTiO3), barium titanate (BaTiO3), magnesium fluoride (MgF2), melamine cyanurate, melamine polyphosphate, melamine trithiocyanate, aluminum diethylphosphite, pentaerythritol and triazine charring agent.

[0070] In an alternative embodiment, based on the total mass of the first heat-resistant strip layer, the first heat-resistant strip layer includes 40 wt% to 96 wt% of first heat-resistant particles, 3 wt% to 59.3 wt% of a binder, and 0.7 wt% to 3 wt% of a dispersant. By controlling the first heat-resistant particles, the binder and the dispersant within the above range, the diaphragm can have good wettability and low impedance. Applying the diaphragm to the battery cell is beneficial to making the battery cell have good charge and discharge performance. Exemplarily, in the first heat-resistant strip layer, it includes 40 wt% of first heat-resistant particles, 59.3 wt% of a binder and 0.7 wt% of a dispersant, includes 60 wt% of first heat-resistant particles, 37 wt% of a binder and 3 wt% of a dispersant or includes 96 wt% of first heat-resistant particles, 3 wt% of a binder and 1 wt% of a dispersant.

[0071] In an alternative embodiment, based on the total mass of the second heat-resistant strip layer, the second heat-resistant strip layer comprises 40 wt% to 96 wt% of second heat-resistant particles, 3 wt% to 59.3 wt% of a binder, and 0.7 wt% to 3 wt% of a dispersant. By controlling the second heat-resistant particles, the binder, and the dispersant within the above ranges, the separator can have good wettability and low impedance. Applying the separator to an electric core is beneficial for the electric core to have good charge and discharge performance. For example, in the second heat-resistant strip layer, it includes 40 wt% of second heat-resistant particles, 59.3 wt% of a binder, and 0.7 wt% of a dispersant, or includes 60 wt% of second heat-resistant particles, 37 wt% of a binder, and 3 wt% of a dispersant, or includes 96 wt% of second heat-resistant particles, 3 wt% of a binder, and 1 wt% of a dispersant. For example, the binder includes at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, a copolymer of vinylidene fluoride and trichloroethylene, polyvinyl acetate, polyvinyl alcohol, polyethylene oxide, polyamide, polyacrylonitrile, an acrylate polymer (such as polymethyl methacrylate), polyacrylic acid, polyacrylate, polyvinyl pyrrolidone, polyethylene ether, styrene-butadiene rubber, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, polytetrafluoroethylene, or polyhexafluoropropylene. The dispersant includes at least one of ethylene oxide, polyamide, polyvinyl alcohol, polyurethane, and polyvinyl pyrrolidone.

[0072] In an alternative embodiment, the thickness of the base film is 4 to 20 μm. For example, the thickness of the base film is 4 μm, 5 μm, 10 μm, 16 μm, 20 μm, or within the range composed of any two of the above values. Among them, in the present application, the base film can be at least one of a woven film, a non-woven film, a polyolefin film, and separator paper. The polyolefin film can be one or more of polyethylene, polypropylene, and a composite material of polyethylene and polypropylene. The elongation at break TD of the substrate is 20% to 200%, and the elongation at break MD is 50% to 300%; the puncture strength is 100 gf to 600 gf; the peel strength between the heat-resistant layer and the substrate layer is 30 to 200 N / m.

[0073] In an alternative embodiment, the separator further includes an adhesive layer, and the adhesive layer is located on the surface of the base film and / or the heat-resistant layer. The setting of the adhesive layer can improve the adhesion between the separator and the electrode sheet, shorten the migration path of lithium ions, thereby improving the high-rate performance; and during the cycling process, the active material on the electrode sheet may generate microcracks due to volume expansion. The adhesion of the adhesive layer can effectively fix the active particles and reduce the capacity attenuation caused by shedding.

[0074] In an alternative embodiment, the thickness of the glue coating layer is 0.5 - 3 μm. The glue coating layer with such a thickness range can effectively improve the adhesion between the separator and the electrode, prevent short circuits caused by contact between the positive and negative electrodes, and enhance the battery safety. For example, the thickness of the glue coating layer is 0.5 μm, 1 μm, 2 μm, 3 μm, or within the range formed by any two of the above values.

[0075] In an alternative embodiment, the glue coating layer comprises a polymer. For example, the polymer includes polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride - hexafluoropropylene, polyimide, polyacrylonitrile, poly(methyl)acrylate, aramid resin, poly(methyl)acrylic acid, styrene - butadiene rubber (SBR), polyvinyl alcohol, polyvinyl acetate, carboxymethyl cellulose (CMC), sodium carboxymethyl cellulose (CMC - Na), carboxyethyl cellulose, polyacrylamide, phenolic resin, epoxy resin, water - based polyurethane, ethylene - vinyl acetate copolymer, polyacrylic acid copolymer, lithium polystyrenesulfonate, water - based silicone resin, nitrile - polyvinyl chloride blend, styrene - acrylic latex, pure benzene latex, etc., and one or more combinations of blends and copolymers derived from the modification of the aforementioned polymers.

[0076] In an alternative embodiment, the particle size Dv10 of the single - crystal nickel - cobalt - manganese ternary cathode material is 0.8 μm - 4 μm, Dv50 is 1 μm - 6 μm, and Dv90 is 3 μm - 10 μm. By controlling the particle size distribution of the single - crystal nickel - cobalt - manganese ternary cathode material within the above range, the battery performance of the battery cell is improved. In particular, Dv10 ≥ 0.8 μm avoids an excessive proportion of ultra - fine particles, and Dv90 ≤ 10 μm inhibits the agglomeration of large particles, making the particle size distribution more concentrated and the packing more compact, thereby increasing the volumetric energy density. For example, the particle size Dv10 of the single - crystal nickel - cobalt - manganese ternary cathode material is 0.8 μm, 1.0 μm, 2.0 μm, 3.0 μm, 4 μm, or within the range formed by any two of the above values, Dv50 is 1 μm, 2 μm, 3 μm, 4 μm, 6 μm, or within the range formed by any two of the above values, and Dv90 is 3 μm, 4 μm, 5 μm, 6 μm, 10 μm, or within the range formed by any two of the above values.

[0077] In an alternative embodiment, the BET of the single - crystal nickel - cobalt - manganese ternary cathode material is 0.5 m 2 / g - 1.4 m 2 / g. The BET is controlled within 0.5 - 1.4 m 2 / g, which not only ensures that a sufficient active surface of the single-crystal nickel cobalt manganese ternary cathode material participates in the reaction (avoiding insufficient reaction activity caused by too low BET), but also avoids side reactions (such as electrolyte decomposition and gas generation) caused by too high BET, thereby improving the cycle performance of the battery cell. For example, the BET of the single-crystal nickel cobalt manganese ternary cathode material is 0.5 m 2 / g, 0.8 m 2 / g, 1.0 m 2 / g, 1.4 m 2 / g or within the range composed of any two of the above values.

[0078] In an alternative embodiment, the particle size Dv10 of the polycrystalline nickel cobalt manganese ternary cathode material is 3 - 13 μm, Dv50 is 6 - 15 μm, and Dv90 is 12 - 25 μm. By controlling the particle size distribution of the polycrystalline nickel cobalt manganese ternary cathode material within the above range, the battery performance of the battery cell is improved. In particular, by controlling Dv90 ≤ 25 μm, it is possible to avoid stress concentration at grain boundaries caused by volume expansion of too large polycrystalline particles during cycling, reduce the generation of microcracks, lower the risk of transition metal (such as Ni, Co) dissolution, and enhance the high-temperature cycle stability. For example, the particle size Dv10 of the polycrystalline nickel cobalt manganese ternary cathode material is 3 μm, 4 μm, 6 μm, 10 μm, 13 μm or within the range composed of any two of the above values, Dv50 is 6 μm, 8 μm, 10 μm, 12 μm, 15 μm or within the range composed of any two of the above values, and Dv90 is 12 μm, 15 μm, 20 μm, 22 μm, 25 μm or within the range composed of any two of the above values.

[0079] In an alternative embodiment, the BET of the polycrystalline nickel cobalt manganese ternary cathode material is 0.3 m 2 / g - 1.0 m 2 / g. By controlling the BET of the polycrystalline nickel cobalt manganese ternary cathode material ≥ 0.3 m 2 / g, it is ensured that the polycrystalline nickel cobalt manganese ternary cathode material has sufficient reaction activity, while BET ≤ 1.0 m 2 / g avoids excessive exposure of the active surface, reduces the continuous decomposition of the electrolyte at the grain boundaries, inhibits gas generation and the thickening of the SEI film, thereby improving the cycle performance of the battery cell. For example, the BET of the polycrystalline nickel cobalt manganese ternary cathode material is 0.3 m 2 / g, 0.5 m 2 / g, 0.8 m 2 / g, 1.0 m 2 / g or within the range composed of any two of the above values.

[0080] In an alternative embodiment, the molar content of nickel element in the single-crystal nickel cobalt manganese ternary cathode material accounts for 85%-98% of the total metal elements of nickel, cobalt and manganese; preferably 90%-95%. The molar content of nickel element in the polycrystalline nickel cobalt manganese ternary cathode material accounts for 80%-95% of the total metal elements of nickel, cobalt and manganese; preferably 87%-92%. On the basis of controlling the weight ratio C of the single-crystal nickel cobalt manganese ternary cathode material to the polycrystalline nickel cobalt manganese ternary cathode material, by controlling the nickel element in the single-crystal and / or polycrystalline nickel cobalt manganese ternary cathode material within the above range, especially within the preferred range, the specific capacity of the material can be significantly improved while maintaining the structural stability and thermal safety of the material, thereby increasing the energy density of the battery. Excessive proportion of nickel element content will lead to an increase in gas production risk and then a decrease in thermal safety. For example, the molar content of nickel element in the single-crystal nickel cobalt manganese ternary cathode material is 85%, 90%, 95%, 97%, 98% or within the range composed of any two of the above values. The molar content of nickel element in the polycrystalline nickel cobalt manganese ternary cathode material is 80%, 85%, 89%, 92%, 95% or within the range composed of any two of the above values.

[0081] In an alternative embodiment, the molar content of cobalt element in the single-crystal nickel cobalt manganese ternary cathode material accounts for 1%-14% of the total metal elements of nickel, cobalt and manganese; preferably 2%-10%. The molar content of cobalt element in the polycrystalline nickel cobalt manganese ternary cathode material accounts for 1%-19% of the total metal elements of nickel, cobalt and manganese; preferably 2%-10%. On the basis of controlling the weight ratio C of the single-crystal nickel cobalt manganese ternary cathode material to the polycrystalline nickel cobalt manganese ternary cathode material, by controlling the cobalt element in the single-crystal and / or polycrystalline nickel cobalt manganese ternary cathode material within the above range, especially within the preferred range, the cycle performance and rate performance of the battery can be significantly improved while maintaining a relatively low cost. For example, the molar content of cobalt element in the single-crystal nickel cobalt manganese ternary cathode material is 1%, 5%, 9%, 12%, 14% or within the range composed of any two of the above values. The molar content of cobalt element in the polycrystalline nickel cobalt manganese ternary cathode material is 1%, 5%, 9%, 12%, 15%, 19% or within the range composed of any two of the above values.

[0082] In an alternative embodiment, the molar content of manganese element in the single-crystal nickel cobalt manganese ternary cathode material accounts for 1%-10% of the total metal elements of nickel, cobalt and manganese; preferably 2%-7%. The molar content of manganese element in the polycrystalline nickel cobalt manganese ternary cathode material accounts for 1%-10% of the total metal elements of nickel, cobalt and manganese; preferably 2%-7%. Manganese mainly plays a role in reducing cost, improving material safety and structural stability in the ternary cathode material. The electrochemical inertness of manganese enables the material to always maintain a stable structure. Excessive manganese content may also cause the material to transform from a layered structure to a spinel structure, increasing the instability of the material. On the basis of controlling the weight ratio C of the above-mentioned single-crystal nickel cobalt manganese ternary cathode material and polycrystalline nickel cobalt manganese ternary cathode material, by controlling the manganese element in the single-crystal and / or polycrystalline nickel cobalt manganese ternary cathode material within the above range, especially within the preferred range, the cost can be reduced, and the battery cycle performance and thermal stability can be improved. For example, the molar content of manganese element in the single-crystal nickel cobalt manganese ternary cathode material is 1%, 5%, 9%, 10% or within the range composed of any two of the above values. The molar content of manganese element in the polycrystalline nickel cobalt manganese ternary cathode material is 1%, 5%, 9%, 10% or within the range composed of any two of the above values.

[0083] In an alternative embodiment, the glue coating layer includes a first glue coating layer provided on the side of the base film facing away from the first heat-resistant strip layer; disposing the first glue coating layer on the side facing away from the first heat-resistant strip layer can improve the adhesion between the separator and the electrode sheet, shorten the migration path of lithium ions, thereby improving the high-rate performance; and during the cycling process, the active material of the electrode sheet may generate microcracks due to volume expansion, and the adhesion of the glue coating layer can effectively fix the active particles and reduce the capacity attenuation caused by shedding.

[0084] In an alternative embodiment, the glue coating layer includes a first glue coating strip layer provided on the side of the first heat-resistant strip layer facing away from the base film.

[0085] In an alternative embodiment, when a second heat-resistant strip layer is provided between two adjacent first heat-resistant strip layers, the glue coating layer further includes a second glue coating strip layer provided on the side of the second heat-resistant strip layer facing away from the base film, and the sum of the thicknesses of the first glue coating strip layer and the first heat-resistant strip layer is greater than the sum of the thicknesses of the second glue coating strip layer and the second heat-resistant strip layer. Through the above settings, it is possible to prevent poor continuity of the glue coating of the separator heat-resistant layer, avoid the problem of insufficient adhesion, and improve the structural stability.

[0086] In an alternative embodiment, the thickness of the first glue coating strip layer is the same as the thickness of the second glue coating strip layer.

[0087] There are no particular limitations on the materials and shapes of the separator used in the lithium-ion secondary battery of the present application, and it can include any techniques disclosed in the prior art.

[0088] The electrolyte used in the lithium-ion secondary battery of the present application can include any techniques disclosed in the prior art.

[0089] The following further describes the present application in detail with specific embodiments, and these embodiments should not be construed as limiting the scope claimed by the present application. In all the embodiments and comparative examples of the present application, the unit wt% represents the mass percentage content.

[0090] Example 1

[0091] This example provides an electrode assembly, including a positive electrode, a negative electrode, an electrolyte, and a separator located between the positive electrode and the negative electrode.

[0092] The separator includes a base film 1 (a polyethylene microporous film with a thickness D of 7 μm, a porosity of 40%, an average pore diameter of 45 nm, and a puncture strength of 300 gf) and a plurality of first heat-resistant strip layers 2 arranged in parallel and spaced apart on one side of the base film, as shown in Figure 1 shown. Based on the total mass of the first heat-resistant strip layer, the first heat-resistant strip layer is composed of 7.5 wt% of heat-resistant particles (specifically boehmite, Dv50 is 0.3 μm), 10 wt% of a binder (polymethyl methacrylate), and 2.5 wt% of a dispersant (ethylene oxide). No second heat-resistant strip layer is provided between two adjacent first heat-resistant strip layers (i.e., the thickness of the second heat-resistant strip layer is 0 μm, H1 - H2 = H1). The thickness H1 of the first heat-resistant strip layer is 1.5 μm, the width A1 is 30 μm, and the spacing width A2 is 20 μm.

[0093] The positive electrode tab includes a positive electrode current collector and positive electrode active layers located on two surfaces of the positive electrode current collector. The positive electrode active material on the positive electrode active material layer is composed of a single-crystalline nickel-cobalt-manganese ternary positive electrode material and a polycrystalline nickel-cobalt-manganese ternary positive electrode material. The mass ratio C of the single-crystalline and polycrystalline nickel-cobalt-manganese ternary positive electrode materials, the relational expressions A1 / A2, and the relational expression A1 / A2×C are shown in Table 1. The molar content of nickel element in the total nickel-cobalt-manganese metal elements in the single-crystalline and polycrystalline nickel-cobalt-manganese ternary positive electrode materials (abbreviated as the molar content of nickel element, denoted as Ni), the molar content of cobalt element in the total nickel-cobalt-manganese metal elements (abbreviated as the molar content of cobalt element, denoted as Co), and the molar content of manganese element in the total nickel-cobalt-manganese metal elements (abbreviated as the molar content of manganese element, denoted as Mn) are shown in Table 2.

[0094] Its preparation method is as follows:

[0095] (1) Preparation of the separator

[0096] 1) Weigh the heat-resistant particles, binder, and dispersant according to the above mass contents for standby. Mix the heat-resistant particles (specifically boehmite, with Dv50 being 0.3 μm), binder (polymethyl methacrylate), dispersant (ethylene oxide), and water that is 1.5 times the total mass of the heat-resistant particles, binder, and dispersant to obtain a ceramic slurry.

[0097] 2) First, engrave a coating roller with corresponding dimensions according to the size (width and thickness, as shown in Table 1) and the spacing width A2 of the first heat-resistant strip layer. The coating roller is engraved with concave and convex patterns. During coating, the slurry enters the concave and convex parts of the coating roller, and then the slurry is coated on the film surface due to contact with the film to be coated. That is, use the coating roller (roller coating method) to coat the ceramic slurry obtained in step 1) on one side of the base film. After high-temperature baking (temperature is 60 °C, time is 30 min), a base film layer with multiple first heat-resistant strip layers arranged in parallel at intervals on one side is obtained; the finished separator is obtained.

[0098] (2) Preparation of the positive electrode sheet

[0099] First, mix the single-crystal nickel cobalt manganese ternary positive electrode material with the molecular formula Li(Ni 0.92 Co 0.05 Mn 0.03 )O2) (the particle size parameters and BET are shown in Table 2) and the polycrystalline nickel cobalt manganese ternary positive electrode material with the molecular formula Li(Ni 0.9 Co 0.05 Mn 0.05 )O2) (the particle size parameters and BET are shown in Table 2) according to the mass ratio in Table 1 to obtain the positive electrode active material. Mix Super-P (conductive carbon black) and activated carbon according to a mass ratio of 1:1 to prepare the conductive agent. Then, mix the positive electrode active material, conductive agent, and binder according to the mass ratio of 97.5% positive electrode active material, 1.35% conductive agent, and 1.15% binder (PVDF), and disperse them in the N-methylpyrrolidone solvent to ensure uniform dispersion to obtain the positive electrode slurry. After that, uniformly coat the obtained positive electrode slurry on both sides of the aluminum foil current collector and perform a drying treatment to form a positive electrode film sheet. Finally, complete the production of the lithium-ion battery positive electrode sheet through the steps of cold pressing, cutting into pieces, and welding electrode tabs.

[0100] (3) Preparation of the negative electrode sheet

[0101] First, use the Si-C composite material as the active material, where the mass content of silicon is 4% and the mass content of graphite is 96%. Mix the active material with Super-P conductive agent, CMC thickener, and SBR binder in a mass ratio of 97.2% Si-C, 0.6% conductive agent, 1.0% thickener, and 1.2% binder. Dissolve these materials in deionized water and stir well to form the negative electrode slurry. Then, evenly coat the negative electrode slurry on both sides of the copper foil current collector and dry it to form the negative electrode film. Finally, complete the preparation of the negative electrode sheet of the lithium-ion battery through the processes of cold pressing, cutting into pieces, and welding the electrode tabs. The distance D mm between the edges of the negative electrode sheets on the same side and the edges of the positive electrode sheets in the width direction of the battery cell, the electrode tab distance L mm, and the relationship D×L are shown in Table 3.

[0102] (4) Preparation of the electrolyte

[0103] Select LiPF6 as the lithium salt, and use ethylene carbonate, diethyl carbonate, methyl ethyl carbonate, and vinylene carbonate to form a mixed solvent in a mass ratio of 8:85:5:2. Subsequently, mix the lithium salt and the solvent in a mass ratio of 8:92 as the electrolyte, which is specifically used for lithium-ion batteries.

[0104] (5) Preparation of the lithium-ion battery

[0105] Select the separator prepared in step (1), wind and assemble the prepared positive electrode sheet, negative electrode sheet, and the manufactured separator into a battery cell, and obtain the lithium-ion battery after processes such as drying and liquid injection and encapsulation.

[0106] The preparation methods of the battery cells in Examples 2 to 4, 6 to 8 are basically the same as those in Example 1, except that only the width A1 or the spacing width A2 of the first heat-resistant strip layer in the separator preparation process is adjusted. Among them, in Examples 3 to 5 and 7, the mass ratio C of the single-crystal and polycrystalline nickel cobalt manganese ternary positive electrode material is also adjusted during the positive electrode sheet preparation process, so that A1 / A2×C is different. See Table 1 for details.

[0107] The preparation method of the battery cell in Example 5 is basically the same as that in Example 1, except that only the mass ratio C of the single-crystal and polycrystalline nickel cobalt manganese ternary positive electrode material is adjusted, so that A1 / A2×C is different. See Table 1 for details.

[0108] The preparation method of the battery cell in Example 9 is basically the same as that in Example 1, except that only the thickness of the first heat-resistant strip layer is adjusted. See Table 1 for details.

[0109] The preparation method of the battery cell in Example 10 is basically the same as that in Example 1, except for the second heat-resistant strip layer 3 between two adjacent first heat-resistant strip layers 2 in the separator, see Figure 2As shown, the thickness of the second heat-resistant strip layer is shown in Table 1, and the composition of the second heat-resistant strip layer is the same as that of the first heat-resistant strip layer. The preparation method of the separator in this example is as follows:

[0110] 1) Weigh the heat-resistant particles, binder, and dispersant according to the above mass contents for standby. Mix the heat-resistant particles (specifically boehmite, Dv50 is 0.3 μm), binder (polymethyl methacrylate), dispersant (ethylene oxide), and water that is 1.5 times the total mass of the heat-resistant particles, binder, and dispersant to obtain a ceramic slurry;

[0111] 2) Pre-engrave a coating roller with corresponding dimensions according to the dimensions (width and thickness, shown in Table 1) of the first heat-resistant strip layer and the second heat-resistant strip layer (the thickness is shown in Table 1, and the width is A2). The coating roller is engraved with concave and convex patterns. When coating, the slurry enters the concave and convex parts of the coating roller, and then the slurry is coated on the film surface due to contact with the film to be coated. That is, use the coating roller (roll coating method) to coat the ceramic slurry obtained in step 1) on one side of the base film. After high-temperature baking (temperature is 60 °C, time is 30 min), a base film layer with the first heat-resistant strip layers arranged in parallel intervals and the second heat-resistant strip layer arranged between two adjacent first heat-resistant strip layers is obtained on one side; the finished separator is obtained.

[0112] The preparation method of the battery cell in Example 11 is basically the same as that in Example 9, except for the second heat-resistant strip layer between two adjacent first heat-resistant strip layers in the separator. The thickness of the second heat-resistant strip layer is shown in Table 1, and the composition of the second heat-resistant strip layer is the same as that of the first heat-resistant strip layer. The preparation method of the separator in this example is the same as that in Example 10.

[0113] The preparation method of the battery cell in Example 12 is basically the same as that in Example 1, except that the particle size Dv50 of the heat-resistant particle boehmite is adjusted during the separator preparation process, as shown in Table 1 in detail.

[0114] The preparation methods of the battery cells in Examples 13 to 14 are basically the same as that in Example 1, except that the contents of each substance in the first heat-resistant strip layer are adjusted during the separator preparation process. Specifically, in Example 13, the first heat-resistant strip layer is composed of 42.3 wt% of heat-resistant particles (specifically boehmite, Dv50 is 0.3 μm), 55.1 wt% of binder (polymethyl methacrylate), and 2.6 wt% of dispersant (ethylene oxide). In Example 14, the first heat-resistant strip layer is composed of 95.8 wt% of heat-resistant particles (specifically boehmite, Dv50 is 0.3 μm), 3.5 wt% of binder (polymethyl methacrylate), and 0.7 wt% of dispersant (ethylene oxide).

[0115] The preparation method of the battery cell in Example 15 is basically the same as that in Example 1, except that, in the preparation process of the diaphragm, after obtaining the base film layer coated with the first heat-resistant strip layer arranged in parallel and spaced intervals on one side in step 2), a first adhesive layer 4 is coated on the single side of the base film 1 away from the first heat-resistant strip layer 2 by roller coating, specifically: polyvinylidene fluoride (PVDF) and dimethylacetamide (DMAC) are mixed, stirred and dissolved to obtain a mixed slurry with a mass concentration of 8wt%, the mixed slurry is coated on the substrate by a gravure roller, DMAC is extracted by water through a water tank, and then dried in a multi-section oven at 60°C (temperature is 60°C, time is 20min) to form a first adhesive layer 4 with a thickness H3 of 1.8μm (see Figure 3 ).

[0116] The preparation method of the battery cell in Example 16 is basically the same as that in Example 1, except that, in the preparation process of the diaphragm, after obtaining the base film layer coated with the first heat-resistant strip layer arranged in parallel and spaced apart on one side in step 2), a roller coating method is also used to perform double-sided coating on the side of the base film away from the first heat-resistant strip layer and the side of the first heat-resistant strip layer away from the base film. Specifically, polyvinylidene fluoride (PVDF) and dimethylacetamide (DMAC) are mixed, and after sufficient stirring and dissolving, a mixed slurry with a mass concentration of 8wt% is obtained, and the mixed slurry is coated on the base film and the first heat-resistant strip layer by a gravure roller, and DMAC is extracted by water through a water tank, and then dried in a multi-section oven at 60°C (temperature is 60°C, time is 20min) to form a first coating layer 4 with a thickness of 1.8μm on the side of the base film 1 away from the first heat-resistant strip layer 2, and at the same time, a first coating strip layer 5 with a thickness H4 of 1.8μm is formed on the side of the first heat-resistant strip layer 2 away from the base film 1 (see Figure 4 shown).

[0117] The preparation method of the battery cell in Example 17 is basically the same as that in Example 10, except that in the process of preparing the separator, after obtaining the base film layer with a first heat-resistant strip layer coated on one side in a parallel and spaced manner in step 2), a roll coating method is also used to perform double-sided coating on the side of the base film facing away from the first heat-resistant strip layer and on the side of the first heat-resistant strip layer facing away from the base film, so that a first glue coating layer is formed on the side of the base film facing away from the first heat-resistant strip layer, a first glue-coated strip layer is formed on the side of the first heat-resistant strip layer facing away from the base film, and a second glue-coated strip layer is formed between adjacent first glue-coated strip layers to obtain a finished separator. Specifically: Polyvinylidene fluoride (PVDF) and dimethylacetamide (DMAC) are mixed and fully stirred and dissolved to obtain a mixed slurry with a mass concentration of 8wt%. The mixed slurry is coated on the base film, the first heat-resistant strip layer and the second heat-resistant layer through a gravure roll, and the DMAC is extracted by water through a water tank, and then dried in a multi-section oven at 60°C (temperature is 60°C, time is 20 min) to form a first glue coating layer 4 with a thickness of 1.8 μm on the side of the base film 1 facing away from the first heat-resistant strip layer 2, and at the same time, a first glue-coated strip layer 5 with a thickness of 1.8 μm is formed on the side of the first heat-resistant strip layer 2 facing away from the base film 1, and a second glue-coated strip layer 6 with a thickness of 1.8 μm is formed on the side of the second heat-resistant strip layer 3 facing away from the base film 1 (see Figure 5 as shown).

[0118] The preparation method of the battery cell in Examples 18 to 21 is basically the same as that in Example 1, except that in the process of preparing the positive electrode sheet, the physical parameters of the single-crystal nickel cobalt manganese ternary positive electrode material and the polycrystalline nickel cobalt manganese ternary positive electrode material used are adjusted, as shown in Table 2 for details.

[0119] The preparation method of the battery cell in Examples 22 to 27 is basically the same as that in Example 1, except that in the process of preparing the positive electrode sheet, the molar content of nickel element, the molar content of cobalt element and / or the molar content of manganese element of the single-crystal or polycrystalline nickel cobalt manganese ternary positive electrode material used are adjusted, as shown in Table 3 for details.

[0120] The preparation method of the battery cell in Examples 28 to 33 is basically the same as that in Example 1, except that the distance D mm and / or the ear margin L mm are adjusted, resulting in different D×L, as shown in Table 4 for details.

[0121] The preparation method of the battery cell in Comparative Example 1 is basically the same as that in Example 1, except that in the process of preparing the positive electrode sheet, only the single-crystal nickel cobalt manganese ternary positive electrode material is used as the positive electrode active material, and its preparation method is the same as that in Example 1.

[0122] The preparation method of the battery cell in Comparative Example 2 is basically the same as that in Example 1, except that in the process of preparing the positive electrode sheet, only the polycrystalline nickel cobalt manganese ternary positive electrode material is used as the positive electrode active material, and its preparation method is the same as that in Example 1.

[0123] The preparation method of the battery cell in Comparative Example 3 is basically the same as that in Example 1, except that the mass ratio C of the single-crystal and polycrystalline nickel cobalt manganese ternary cathode material is adjusted, resulting in different A1 / A2×C. See Table 1 for details.

[0124] The preparation method of the battery cell in Comparative Example 4 is basically the same as that in Example 1, except that the width A1, the spacing width A2 of the first heat-resistant strip layer in the diaphragm preparation process and the mass ratio C of the single-crystal and polycrystalline nickel cobalt manganese ternary cathode material are adjusted, resulting in different A1 / A2×C. See Table 1 for details.

[0125] Table 1 Physical parameters of the diaphragm and the positive active material

[0126]

[0127] " / " indicates non-existence.

[0128] Table 2 Physical parameters of the positive active material

[0129]

[0130] Table 3 Molar content of metal elements in the positive active material

[0131]

[0132] Table 4 Parameters of the negative electrode sheet

[0133] D L D×L Example 1 1.5 20 30 Example 28 0.5 20 10 Example 29 1.5 50 75 Example 30 2.5 40 100 Example 31 5 20 100 Example 32 0.5 10 5 Example 33 3 50 150

[0134] Test example

[0135] Take the lithium-ion batteries prepared in each example and comparative example for the following tests:

[0136] 1. Minimum remaining charge (SOC) test

[0137] Wrap the battery cell with a foam material, monitor the surface temperature of the battery cell, put it into a constant temperature box, and adjust the constant temperature box to 25°C for steps (1) to (5).

[0138] (1) Stand for 5 min; (2) Constant current discharge at 0.5C to the lower limit voltage; (3) Stand for 15 min; (4) Constant current charge at 1.8C to the upper limit voltage, cut-off current 0.05C; Stand for 30 min; (5) Repeat steps (2) to (4) to obtain the full charge capacity C0.

[0139] Then, perform steps (6) to (11) until the discharge cut-off voltage = the lower limit voltage (2.5V ± 0.05V) at the target temperature and SOC.

[0140] (6) Adjust the thermostat to 0°C and leave it for 120 min; (7) Constant current discharge for 15 s at 0°C and 7.5 C, sampling frequency (100 ms), and test the discharge cut-off voltage; (8) Adjust the thermostat to 25°C and leave it for 30 min; (9) Discharge at 1 C to reduce the SOC or charge at 1 C to increase the SOC at 25°C (if the SOC is lower than the target SOC, charge; if it is higher than the target SOC, discharge, and the target SOC is the SOC at which the discharge cut-off voltage is equal to the lower limit voltage); (10) Adjust the thermostat to 25°C and leave it for 90 min; (11) Repeat (7) to (10) until the discharge cut-off voltage tested in (7) = the lower limit voltage (2.5 V ± 0.05 V).

[0141] 2. Cycle performance test

[0142] At an ambient temperature of 25 ± 2°C, charge at 0.5 C to the upper limit cut-off voltage, constant voltage to 0.05 C, leave it static for 10 min, then discharge at 1 C to the lower limit cut-off voltage. The initial discharge capacity is denoted as C0, and leave it static for 10 min. Cycling mode: Charge at 3 C to the upper limit cut-off voltage, constant voltage to 0.05 C, leave it static for 10 min, discharge at 10 C to the lower limit cut-off voltage, and leave it static for 20 min. After 600 cycles, charge at 0.5 C to the upper limit cut-off voltage, constant voltage to 0.05 C, leave it static for 10 min, then discharge at 1 C to the lower limit cut-off voltage. The final discharge capacity is denoted as C1.

[0143] Capacity retention rate: C = C1 / C0 * 100%.

[0144] 3. Rate performance test

[0145] Leave the lithium-ion battery at 25°C for 5 minutes; discharge at 0.5 C to 2.5 V, charge at 1 C to 4.2 V, constant voltage to 0.05 C, and discharge at 0.2 C to obtain the initial capacity; leave it for 30 min; at room temperature, charge at 1 C to 100% SOC; leave it for 15 minutes, leave it static at 0°C for 2 h, discharge at a rate of 15 C to the lower limit voltage, and record the discharge capacity. Calculate the 15 C discharge capacity retention rate of the battery using the following formula.

[0146] 15 C discharge capacity retention rate (%) = discharge capacity / initial capacity × 100%.

[0147] 4. Thermal stability and safety test

[0148] Discharge the lithium-ion battery at 0.5 C and charge it to full standard at 1 C; place the lithium-ion battery in a thermal chamber and raise the temperature to 130°C at a rate of (5°C ± 2°C) / min and hold for 60 min to end the experiment. Record the state of the lithium-ion battery before and after the test. If the lithium-ion battery catches fire, the furnace temperature test fails. Test 20 cells at a time, and express the furnace temperature pass rate as "the number of lithium-ion batteries with a passing furnace temperature test / the total number of lithium-ion batteries".

[0149] Please refer to Table 5 for the test results of the above items.

[0150] Table 5 Performance Test Results

[0151]

[0152]

[0153] The results show that, compared with Comparative Examples 1-4, the battery cells provided by the embodiments of the present invention use a combination of a single-crystal nickel cobalt manganese ternary cathode material and a polycrystalline nickel cobalt manganese ternary cathode material for the separator, and by strictly controlling the mutual relationship between the weight ratio C of the two materials and the width A1 and the spacing width A2 of the first heat-resistant strip layer, the cycle stability of the battery system of the ternary cathode material is significantly improved on the basis of maintaining high thermal safety, enabling the battery to still take into account high cycle performance and excellent rate performance in the scenario of fast charge and discharge at a high rate.

[0154] Obviously, the above embodiments are only examples given for clear illustration and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or variations can be made on the basis of the above description. It is not necessary and impossible to list all the implementation manners here. And the obvious changes or variations derived therefrom are still within the protection scope of the present invention.

Claims

1. A battery cell, characterized in that: The invention comprises a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator located between the positive electrode sheet and the negative electrode sheet, wherein the separator comprises a base film and a heat-resistant layer located on at least one side of the base film, wherein the heat-resistant layer comprises a plurality of first heat-resistant strip layers spaced apart from each other and a second heat-resistant strip layer disposed between two adjacent first heat-resistant strip layers, wherein the thickness H1 of the first heat-resistant strip layer and the thickness H2 of the second heat-resistant strip layer satisfy: 0 μm<H1-H2≤H1, wherein the units of H1 and H2 are both μm; The positive electrode sheet comprises a current collector and a positive electrode active material layer disposed on at least one side of the current collector, wherein the positive electrode active material layer comprises a positive electrode active material, and the positive electrode active material comprises a single crystal nickel-cobalt-manganese ternary positive electrode material and a polycrystalline nickel-cobalt-manganese ternary positive electrode material; The width A1 of the first heat-resistant strip layer, the interval width A2 between two adjacent first heat-resistant strip layers, and the weight ratio C of the single-crystal nickel-cobalt-manganese ternary positive electrode material to the polycrystalline nickel-cobalt-manganese ternary positive electrode material in the positive electrode active material layer satisfy the following relationship: 2.5≤(A1 / A2)×C≤20; where the units of A1 and A2 are both μm.

2. The battery cell according to claim 1, characterized in that: The distance D mm between the edge of the negative electrode sheet and the edge of the positive electrode sheet on the same side in the width direction of the battery cell and the tab margin L mm satisfy the following relationship: 10≤D×L≤100; wherein D is 0.1-3, and L is 6-50.

3. The battery cell according to claim 1, characterized in that: 4.5≤(A1 / A2)×C≤15; And / or, 1μm≤H1-H2≤5μm.

4. The battery cell according to claim 1, characterized in that: A1: 30μm-100μm; and / or, A2 is 6.7 μm-20 μm; and / or, 1.5≤A1 / A2≤4.5; and / or, C is 1-4; and / or, 0.5 μm ≤ H1 ≤ 10 μm; And / or, 0.5μm≤H2≤8μm.

5. The battery cell according to any one of claims 1 to 4, characterized in that: The battery cell meets one or more of the following conditions: A. The first heat-resistant strip layer includes first heat-resistant particles; B. The second heat-resistant strip layer includes second heat-resistant particles; C. The diaphragm further comprises a coating layer, and the coating layer is located on the surface of the base film and / or the heat-resistant layer.

6. The battery cell according to claim 5, characterized in that: The battery cell meets one or more of the following conditions: A. The particle size Dv50 of the first heat-resistant particles is 0.1 μm to 2.5 μm; B. The components of the first heat-resistant particles include at least one of boehmite (γ-AlOOH), aluminum oxide (Al2O3), barium sulfate (BaSO4), magnesium oxide (MgO), magnesium hydroxide (Mg(OH)2), silicon dioxide (SiO2), tin dioxide (SnO2), titanium oxide (TiO2), calcium oxide (CaO), zinc oxide (ZnO), zirconium oxide (ZrO2), yttrium oxide (Y2O3), nickel oxide (NiO), cerium oxide (CeO2), zirconium titanate (SrTiO3), barium titanate (BaTiO3), magnesium fluoride (MgF2), melamine cyanurate, melamine polyphosphate, melamine thiocyanate, diethyl aluminum hypophosphite, pentaerythritol and triazine carbon former; C. Based on the total mass of the first heat-resistant strip layer, the first heat-resistant strip layer comprises 40wt% to 96wt% of first heat-resistant particles, 3wt% to 59.3wt% of a binder and 0.7wt% to 3wt% of a dispersant; D. The particle size Dv50 of the second heat-resistant particles is 0.1 μm to 2.5 μm; E. The components of the second heat-resistant particles include at least one of boehmite (γ-AlOOH), aluminum oxide (Al2O3), barium sulfate (BaSO4), magnesium oxide (MgO), magnesium hydroxide (Mg(OH)2), silicon dioxide (SiO2), tin dioxide (SnO2), titanium oxide (TiO2), calcium oxide (CaO), zinc oxide (ZnO), zirconium oxide (ZrO2), yttrium oxide (Y2O3), nickel oxide (NiO), cerium oxide (CeO2), zirconium titanate (SrTiO3), barium titanate (BaTiO3), magnesium fluoride (MgF2), melamine cyanurate, melamine polyphosphate, melamine thiocyanate, diethyl aluminum hypophosphite, pentaerythritol and triazine carbon former; F. Based on the total mass of the second heat-resistant strip layer, the second heat-resistant strip layer comprises 40wt% to 96wt% of second heat-resistant particles, 3wt% to 59.3wt% of a binder and 0.7wt% to 3wt% of a dispersant; G. The thickness of the coating layer is 0.5-3 μm; H. The coating layer includes a polymer.

7. The battery cell according to any one of claims 1 to 4, characterized in that: The particle size Dv10 of the single crystal nickel-cobalt-manganese ternary positive electrode material is 0.8 μm-4 μm, Dv50 is 1 μm-6 μm, and Dv90 is 3 μm-10 μm; And / or, the BET of the single crystal nickel-cobalt-manganese ternary positive electrode material is 0.5m 2 / g-1.4m 2 / g; And / or, the particle size Dv10 of the polycrystalline nickel-cobalt-manganese ternary positive electrode material is 3 μm-13 μm, Dv50 is 6 μm-15 μm, and Dv90 is 12 μm-25 μm; And / or, the BET of the polycrystalline nickel-cobalt-manganese ternary positive electrode material is 0.3m 2 / g-1.0m 2 / g.

8. The battery cell according to any one of claims 1 to 4, characterized in that: The molar content of nickel in the single crystal nickel-cobalt-manganese ternary positive electrode material accounts for 85%-98% of the total metal elements of nickel, cobalt and manganese; And / or, the molar content of nickel in the polycrystalline nickel-cobalt-manganese ternary positive electrode material accounts for 80%-95% of the total metal elements of nickel, cobalt and manganese; And / or, the molar content of cobalt element in the single crystal nickel-cobalt-manganese ternary positive electrode material accounts for 1%-14% of the total metal elements of nickel, cobalt and manganese; And / or, the molar content of cobalt element in the polycrystalline nickel-cobalt-manganese ternary positive electrode material accounts for 1%-19% of the total metal elements of nickel, cobalt and manganese; And / or, the molar content of manganese element in the single crystal nickel-cobalt-manganese ternary positive electrode material accounts for 1%-10% of the total metal elements of nickel, cobalt and manganese; And / or, the molar content of manganese element in the polycrystalline nickel-cobalt-manganese ternary positive electrode material accounts for 1%-10% of the total metal elements of nickel, cobalt and manganese.

9. The battery cell according to claim 8, characterized in that: In the single crystal nickel-cobalt-manganese ternary positive electrode material, the molar content of nickel element in the total metal elements of nickel, cobalt and manganese is 90%-95%; And / or, the molar content of nickel in the polycrystalline nickel-cobalt-manganese ternary positive electrode material accounts for 87%-92% of the total metal elements of nickel, cobalt and manganese; And / or, the molar content of cobalt element in the single crystal nickel-cobalt-manganese ternary positive electrode material accounts for 2%-10% of the total metal elements of nickel, cobalt and manganese; And / or, the molar content of cobalt element in the polycrystalline nickel-cobalt-manganese ternary positive electrode material accounts for 2%-10% of the total metal elements of nickel, cobalt and manganese; And / or, the molar content of manganese in the single crystal nickel-cobalt-manganese ternary positive electrode material accounts for 2%-7% of the total metal elements of nickel, cobalt and manganese; And / or, the molar content of manganese element in the polycrystalline nickel-cobalt-manganese ternary positive electrode material accounts for 2%-7% of the total metal elements of nickel, cobalt and manganese.

10. An electrochemical device, characterized in that: A battery cell comprising the battery cell described in any one of claims 1 to 9.

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