Secondary battery and electronic apparatus

Abstract

Provided are a secondary battery and an electronic apparatus. The secondary battery comprises a positive electrode sheet, a negative electrode sheet and an electrolyte. The positive electrode sheet comprises a positive-electrode current collector, and a first material layer and a second material layer that are disposed on a surface of the positive-electrode current collector, wherein the first material layer is located between the positive-electrode current collector and the second material layer, and the first material layer comprises a first positive electrode material, in which the molar percentage of nickel is N1; the second material layer comprises a second positive electrode material, in which the molar percentage of nickel is N2; and N1>N2. The electrolyte contains an additive, which includes at least one of carboxylate ester, fluorinated carboxylate ester, ethyl propionate, propyl propionate, ethyl fluoroacetate, ethylene sulfate and bicyclic sulfate, wherein on the basis of the mass of the electrolyte, the mass percentage W of the additive ranges from 1% to 20%. The secondary battery has the features, thereby improving the energy density while mitigating the internal gas generation of the secondary battery.

Description

Secondary batteries and electronic devices

[0001] This application claims priority to Chinese Patent Application No. 202510368356.9, filed on March 26, 2025, entitled "A Secondary Battery and Electronic Device", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of electrochemical technology, and in particular to a secondary battery and electronic device. Background Technology

[0003] Secondary batteries are widely used due to their advantages such as high specific energy and long cycle life. Among them, the use of ternary cathode materials can effectively improve the energy density of batteries. However, during the manufacturing process of secondary batteries containing ternary cathode materials, the ternary cathode materials are easily exposed to air and absorb water, which increases the water content of the cathode sheet. This results in an excessively high residual alkali content in the cathode material layer, leading to severe gas generation and high cycle expansion rate during the charging and discharging process of the secondary battery. Summary of the Invention

[0004] The purpose of this application is to provide a secondary battery and electronic device that balances internal gas production and energy density of the secondary battery.

[0005] It should be noted that while this application uses lithium-ion batteries as an example of secondary batteries to explain the invention, the secondary batteries in this application are not limited to lithium-ion batteries. The specific technical solution is as follows:

[0006] The first aspect of this application provides a secondary battery comprising a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a positive current collector and a first material layer and a second material layer disposed on the surface of the positive current collector, the first material layer being located between the positive current collector and the second material layer. The first material layer includes a first positive electrode material comprising nickel, cobalt, and manganese, and the molar percentage of nickel in the first positive electrode material is N1 based on the total molar amount of non-lithium metal elements in the first positive electrode material. The second material layer includes a second positive electrode material comprising nickel, cobalt, and manganese, and the molar percentage of nickel in the second positive electrode material is N2 based on the total molar amount of non-lithium metal elements in the second positive electrode material; N1 > N2. The electrolyte includes additives, the additives being at least one selected from carboxylic acid esters, fluorocarboxylic acid esters, ethyl propionate, propyl propionate, ethyl fluoroacetate, vinyl sulfate, and bicyclic sulfate, and the mass percentage W of the additives is 1% to 20% based on the mass of the electrolyte. The secondary battery meets the above characteristics. During the preparation of the positive electrode sheet, the water absorption is reduced, the generation of residual alkali in the positive electrode material layer is reduced, and the electrolyte containing the above additives is matched. This helps to reduce the generation of gas in the secondary battery during charging and discharging, improve the internal gas generation of the secondary battery while taking into account the energy density.

[0007] In one embodiment of this application, 70% ≤ N1 ≤ 95%, and 30% ≤ N2 ≤ 50%. By adjusting the values ​​of N1 and N2 within the range of this application, the first material layer has a higher nickel content, which is beneficial to improving the energy density of the secondary battery. The second material layer has a lower nickel content and is located on the outside of the first material layer. During the preparation process, this helps to reduce the water absorption on the surface of the positive electrode, thereby reducing the amount of residual alkali generated on the surface of the positive electrode. At the same time, by reducing the contact between the high-nickel first material layer and the external environment, the overall amount of residual alkali generated in the positive electrode material layer during the preparation process is reduced, thereby reducing the gas generation during the charging and discharging process of the secondary battery. This further improves the internal gas generation of the secondary battery while maintaining energy density.

[0008] In some embodiments of this application, 80% ≤ N1 ≤ 90%, and / or 33% ≤ N2 ≤ 40%. By adjusting the values ​​of N1 and N2 within the range of this application, the first material layer has a higher nickel content, which is beneficial to improving the energy density of the secondary battery. The second material layer has a lower nickel content and is located outside the first material layer. During the preparation process, it is beneficial to reduce the water absorption on the surface of the positive electrode, thereby reducing the amount of residual alkali generated on the surface of the positive electrode. At the same time, by reducing the contact between the high-nickel first material layer and the external environment, the overall amount of residual alkali generated in the positive electrode material layer during the preparation process is reduced, thereby reducing the gas generation during the charging and discharging process of the secondary battery. This further improves the internal gas generation of the secondary battery while maintaining energy density.

[0009] In one embodiment of this application, the additive includes at least one of ethyl fluoroacetate and vinyl sulfate. By adjusting the additive in the electrolyte within the above-mentioned range, it is beneficial to suppress the dissolution of transition metals and to prevent side reactions with the first and second material layers, thereby further improving the internal gas generation of the secondary battery.

[0010] In one embodiment of this application, 3% ≤ W ≤ 10%. By controlling the mass percentage content W of the additive within the range of this application, it is beneficial to suppress the dissolution of transition metals and to prevent side reactions with the first material layer and the second material layer, thereby further improving the internal gas generation of the secondary battery during the charging and discharging process.

[0011] In one embodiment of this application, the coating mass per unit area of ​​the first material layer is CW1, and the coating mass per unit area of ​​the second material layer is CW2, with 50% ≤ CW1 / (CW1+CW2)×100% ≤ 90% and 10% ≤ CW2 / (CW1+CW2)×100% ≤ 50%. Within the scope of this application, by adjusting the value of CW1 / (CW1+CW2), the percentage of coating mass per unit area of ​​the first material layer with a higher nickel content is higher. This is beneficial for providing more battery capacity under the same mass of the secondary battery, thus improving the energy density of the secondary battery. Simultaneously, by adjusting the value of CW2 / (CW1+CW2), within the scope of this application, the percentage of coating mass per unit area of ​​the second material layer is lower, and it is located outside the first material layer, resulting in greater contact with air. This helps reduce the amount of residual alkali generated on the surface of the positive electrode during the preparation process. Furthermore, by reducing the contact between the high-nickel first material layer and the external environment, the overall amount of residual alkali generated in the positive electrode material layer during preparation is reduced, thus reducing gas generation during the charging and discharging process of the secondary battery. Therefore, the first and second material layers are matched to further improve the internal gas generation of the secondary battery while maintaining energy density.

[0012] In one embodiment of this application, 70% ≤ CW1 / (CW1+CW2)×100% ≤ 80%, and / or, 10% ≤ CW2 / (CW1+CW2)×100% ≤ 30%. By adjusting the value of CW1 / (CW1+CW2) within the scope of this application, the percentage of coating mass per unit area of ​​the first material layer with a higher nickel content is higher, which is beneficial to providing more battery capacity under the same mass of the secondary battery, and is beneficial to improving the energy density of the secondary battery. At the same time, by adjusting the value of CW2 / (CW1+CW2) within the scope of this application, the percentage of coating mass per unit area of ​​the second material layer is lower and it is located on the outside of the first material layer, with more contact with air. This is beneficial to reduce the amount of residual alkali generated on the surface of the positive electrode during the preparation process. At the same time, by reducing the contact between the high-nickel first material layer and the external environment, the overall amount of residual alkali generated in the positive electrode material layer during the preparation process is reduced, and the gas generation during the charging and discharging process of the secondary battery is reduced. Thus, the first and second material layers are matched with each other, further improving the internal gas production of the secondary battery while also taking into account energy density.

[0013] In one embodiment of this application, 150mg / 1540.24mm 2 ≤CW1+CW2≤350mg / 1540.24mm 2 By adjusting the values ​​of CW1+CW2 within the range of this application, the resulting cathode material layer has a suitable coating quality per unit area, and the first and second material layers work together to further improve the energy density of the secondary battery.

[0014] In one embodiment of this application, 200mg / 1540.24mm 2 ≤CW1+CW2≤300mg / 1540.24mm 2 By adjusting the values ​​of CW1+CW2 within the range of this application, the resulting cathode material layer has a suitable coating quality per unit area, and the first and second material layers work together to further improve the energy density of the secondary battery.

[0015] In one embodiment of this application, the first cathode material and the second cathode material each independently include a dopant element, which includes at least one selected from aluminum, magnesium, titanium, tungsten, zirconium, iridium, molybdenum, or vanadium. Based on the mass of the first cathode material, the molar percentage W1 of the dopant element in the first cathode material is 0.5% to 5%; based on the mass of the second cathode material, the molar percentage W2 of the dopant element in the second cathode material is 0.1% to 3%. The dopant elements of the first cathode material and the second cathode material are selected from the above range, and controlling the molar percentage within the range of this application is beneficial to improving the structural stability of the first cathode material and the second cathode material, reducing the probability of side reactions, thereby reducing gas generation during the charging and discharging process of the secondary battery, and further improving the internal gas generation of the secondary battery.

[0016] In some embodiments of this application, 1% ≤ W1 ≤ 3%, and / or 0.5% ≤ W2 ≤ 1%. By adjusting the molar percentage of doping elements in the first and second cathode materials within the range of this application, it is beneficial to improve the structural stability of the first and second cathode materials, reduce the probability of side reactions, thereby reducing gas generation during the charging and discharging process of the secondary battery, and further improving the internal gas generation of the secondary battery.

[0017] In one embodiment of this application, the first material layer includes a first adhesive and a second adhesive, and the second material layer includes a third adhesive; the first adhesive and the third adhesive each independently include at least one of polyvinylidene fluoride, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyamide-imide, and styrene-butadiene rubber; the second adhesive includes at least one of polyacrylic acid and sulfonated polymer, wherein the sulfonated polymer includes at least one of perfluorosulfonic acid resin, sulfonated polyether ether ketone, sulfonated polystyrene, sulfonated polyimide, and sulfonated polyarylene ether sulfone. The first binder, second binder, and third binder are selected from the above-mentioned materials. The second binder is acidic and, when combined with the first material layer with high nickel content, helps to neutralize the residual alkali generated by the first material layer during the preparation process, thereby reducing the overall residual alkali content of the positive electrode material layer. This helps to reduce gas generation during the charging and discharging process of the secondary battery. At the same time, it works synergistically with the first and third binders to improve the adhesion between the overall positive electrode material layer and the positive electrode current collector, improve the internal resistance of the secondary battery, and thus help to improve the cycle performance of the secondary battery.

[0018] In one embodiment of this application, the mass percentage W of the first adhesive is based on the mass of the first material layer. N1 The mass percentage of the second adhesive W N2 0.5% ≤ W N1 +W N2 ≤2.5%, 0.3%≤WN2 ≤1.5%; and / or, based on the mass percentage of the second material layer, W of the third adhesive. N3 It ranges from 0.5% to 2.5%. This is achieved by adjusting W... N1 +W N2 value, W N2 Within the scope of this application, the acidic second binder is beneficial for neutralizing the residual alkali generated by the first positive electrode material during the preparation of the positive electrode sheet, reducing the probability of excessive gas generation during the charging and discharging of the secondary battery due to the high residual alkali content, further improving the internal gas generation of the secondary battery. Simultaneously, it works synergistically with the first binder to improve the adhesion between the first material layer, the second binder layer, and the positive electrode current collector; regulating W... N3 Within the scope of this application, the third binder works synergistically with the first and second binders to improve the adhesion between the overall positive electrode material layer and the positive electrode current collector, thereby further improving the cycle performance of the secondary battery while also taking into account the energy density.

[0019] In one embodiment of this application, the secondary battery satisfies at least one of the following characteristics: (1) the mass percentage of the first positive electrode material is greater than or equal to 85% based on the mass of the first material layer; (2) the mass percentage of the second positive electrode material is greater than or equal to 85% based on the mass of the second material layer; and (3) the first and second positive electrode materials each independently include lithium nickel cobalt manganese oxide. Within the scope of this application, by controlling the mass percentage of the first and second positive electrode materials, the first positive electrode material is the main material of the first material layer, and the first positive electrode material has a high nickel content, resulting in a secondary battery with a high energy density; the second positive electrode material is the main material of the second material layer, and the second material layer has more contact with air, and the second positive electrode material has a suitable nickel content, which is beneficial to reducing the amount of residual alkali generated in the positive electrode material layer during the preparation process, reducing gas production in the secondary battery during charging and discharging, thereby improving the internal gas production of the secondary battery while maintaining energy density.

[0020] A second aspect of this application provides an electronic device comprising the secondary battery described in the first aspect of this application.

[0021] The beneficial effects of this application are:

[0022] This application provides a secondary battery comprising a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a positive current collector and a first material layer and a second material layer disposed on the surface of the positive current collector, the first material layer being located between the positive current collector and the second material layer. The first material layer includes a first positive electrode material comprising nickel, cobalt, and manganese, and the molar percentage of nickel in the first positive electrode material is N1 based on the total molar amount of non-lithium metal elements in the first positive electrode material. The second material layer includes a second positive electrode material comprising nickel, cobalt, and manganese, and the molar percentage of nickel in the second positive electrode material is N2 based on the total molar amount of non-lithium metal elements in the second positive electrode material; N1 > N2. The electrolyte includes additives, the additives being at least one selected from carboxylic acid esters, fluorocarboxylic acid esters, ethyl propionate, propyl propionate, ethyl fluoroacetate, vinyl sulfate, and bicyclic sulfate, and the mass percentage W of the additives is 1% to 20% based on the mass of the electrolyte. The secondary battery meets the above characteristics. During the preparation of the positive electrode sheet, the water absorption is reduced, the generation of residual alkali in the positive electrode material layer is reduced, and the electrolyte containing the above additives is matched. This helps to reduce the generation of gas in the secondary battery during charging and discharging, improve the internal gas generation of the secondary battery while taking into account the energy density.

[0023] Of course, implementing any product or method of this application does not necessarily require achieving all of the advantages described above at the same time. Attached Figure Description

[0024] The accompanying drawings, which are provided to further illustrate this application and form part of this application, illustrate exemplary embodiments of this application and are used to explain this application, but do not constitute an undue limitation of this application.

[0025] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other embodiments can be obtained based on these accompanying drawings.

[0026] Figure 1 is a schematic diagram of the structure of the positive electrode sheet along its own thickness direction in one embodiment of this application. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are merely some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0028] It should be noted that, in the specific embodiments of this application, a lithium-ion battery is used as an example of a secondary battery to explain this application; however, the secondary battery in this application is not limited to lithium-ion batteries. The specific technical solution is as follows:

[0029] The first aspect of this application provides a secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, as shown in FIG1. ​​The positive electrode 10 includes a positive current collector 110 and a first material layer 120 and a second material layer 130 disposed on the surface of the positive current collector 110, wherein the first material layer 120 is located between the positive current collector 110 and the second material layer 130. The first material layer includes a first positive electrode material comprising nickel, cobalt, and manganese. Based on the total molar amount of non-lithium metal elements in the first positive electrode material, the molar percentage of nickel in the first positive electrode material is N1. The second material layer includes a second positive electrode material comprising nickel, cobalt, and manganese. Based on the total molar amount of non-lithium metal elements in the second positive electrode material, the molar percentage of nickel in the second positive electrode material is N2; N1 > N2. The high nickel content in ternary cathode materials provides high energy density, but excessively high nickel content leads to water absorption during cathode preparation, increasing the water content, especially on the surface. This results in excessive residual alkali content in the cathode material layer, exacerbating internal gas generation during charging and discharging. Therefore, by controlling the molar percentage of nickel in the first and second cathode materials to achieve the aforementioned relationship, the first material layer, with its higher nickel content, provides higher energy density. The second material layer, with its lower nickel content and location on the outer side of the first layer, has greater contact with air, reducing water absorption on the cathode surface and thus decreasing residual alkali formation. Simultaneously, reducing the contact between the high-nickel first material layer and the external environment decreases water absorption, further reducing residual alkali formation and gas generation during charging and discharging. This improves internal gas generation while maintaining energy density.

[0030] In one embodiment of this application, the electrolyte includes an additive, which includes at least one selected from carboxylic acid esters, fluorocarboxylic acid esters, ethyl propionate, propyl propionate, ethyl fluoroacetate, vinyl sulfate, and bicyclic sulfate. Based on the mass of the electrolyte, the mass percentage W of the additive is 1% to 20%. In one embodiment of this application, 3% ≤ W ≤ 10%. For example, the mass percentage W of the additive can be 1%, 2%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, or a range consisting of any two of these values. When the mass percentage of the additive is too small, for example, less than 1%, it has little effect on improving the internal gas generation of the secondary battery; when the mass percentage of the additive is too large, for example, greater than 20%, it is easy to form a thick solid electrolyte interphase (SEI) film on the surface of the negative electrode, thus affecting the cycle performance of the secondary battery. Therefore, by introducing the above-mentioned additive into the electrolyte and controlling its mass percentage W within the scope of this application, the dissolution of transition metals can be suppressed, and it is less likely to undergo side reactions with the first material layer and the second material layer, thereby improving the internal gas generation of the secondary battery during the charging and discharging process.

[0031] Therefore, the secondary battery meets the above characteristics, reducing water absorption during the preparation of the positive electrode sheet and reducing the generation of residual alkali in the overall positive electrode material layer. At the same time, the electrolyte containing the above additives helps to reduce gas generation during the charging and discharging process of the secondary battery, thereby improving the internal gas generation of the secondary battery while taking into account the energy density.

[0032] In one embodiment of this application, 70% ≤ N1 ≤ 95%. In some embodiments of this application, 80% ≤ N1 ≤ 90%. For example, N1 can be 70%, 72%, 74%, 76%, 78%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 92%, 94%, 95%, or a range of any two of these values. In one embodiment of this application, 30% ≤ N2 ≤ 50%. In one embodiment of this application, 33% ≤ N2 ≤ 40%. For example, N2 can be 30%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 42%, 44%, 46%, 48%, 50%, or a range of any two of these values. By adjusting the values ​​of N1 and N2 within the scope of this application, the first material layer has a higher nickel content, which is beneficial to improving the energy density of the secondary battery. The second material layer has a lower nickel content and is located outside the first material layer. During the preparation process, it is beneficial to reduce the water absorption on the surface of the positive electrode, thereby reducing the amount of residual alkali generated on the surface of the positive electrode. At the same time, by reducing the contact between the high-nickel first material layer and the external environment, the overall amount of residual alkali generated in the positive electrode material layer during the preparation process is reduced, thereby reducing the gas generation during the charging and discharging process of the secondary battery. This further improves the internal gas generation of the secondary battery while maintaining energy density.

[0033] In one embodiment of this application, the additive includes at least one of ethyl fluoroacetate and vinyl sulfate. By adjusting the additive in the electrolyte within the above-mentioned range, it is beneficial to suppress the dissolution of transition metals and to prevent side reactions with the first and second material layers, thereby further improving the internal gas generation of the secondary battery.

[0034] In one embodiment of this application, the coating mass per unit area of ​​the first material layer is CW1, and the coating mass per unit area of ​​the second material layer is CW2, with 50% ≤ CW1 / (CW1+CW2)×100% ≤ 90%. In another embodiment of this application, 70% ≤ CW1 / (CW1+CW2)×100% ≤ 80%. For example, the value of CW1 / (CW1+CW2) can be 50%, 55%, 60%, 65%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 85%, 90%, or a range consisting of any two of these ratios. In another embodiment of this application, 10% ≤ CW2 / (CW1+CW2)×100% ≤ 50%. In one embodiment of this application, 10% ≤ CW2 / (CW1+CW2)×100% ≤ 30%. For example, the value of CW2 / (CW1+CW2) can be 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, 35%, 40%, 45%, 50%, or a range of any two of these ratios. Within the scope of this application, by adjusting the value of CW1 / (CW1+CW2), the percentage of coating mass per unit area of ​​the first material layer with a higher nickel content is higher. This is beneficial for providing more battery capacity under the same mass of the secondary battery, thus improving the energy density of the secondary battery. Simultaneously, by adjusting the value of CW2 / (CW1+CW2), within the scope of this application, the percentage of coating mass per unit area of ​​the second material layer is lower, and it is located outside the first material layer, resulting in greater contact with air. This helps reduce the amount of residual alkali generated on the surface of the positive electrode during the preparation process. Furthermore, by reducing the contact between the high-nickel first material layer and the external environment, the overall amount of residual alkali generated in the positive electrode material layer during preparation is reduced, thus reducing gas generation during the charging and discharging process of the secondary battery. Therefore, the first and second material layers are matched to further improve the internal gas generation of the secondary battery while maintaining energy density.

[0035] In one embodiment of this application, 150mg / 1540.24mm 2 ≤CW1+CW2≤350mg / 1540.24mm 2 In one embodiment of this application, 200mg / 1540.24mm 2 ≤CW1+CW2≤300mg / 1540.24mm 2 For example, CW1+CW2 can be 150mg / 1540.24mm. 2 180mg / 1540.24mm 2 200mg / 1540.24mm 2 220mg / 1540.24mm 2250mg / 1540.24mm 2 280mg / 1540.24mm 2 300mg / 1540.24mm 2 320mg / 1540.24mm 2 350mg / 1540.24mm 2 It can be a range consisting of any two of these values. By adjusting the values ​​of CW1+CW2 within the range of this application, the resulting cathode material layer has a suitable coating quality per unit area, and the first and second material layers work together to further improve the energy density of the secondary battery.

[0036] In one embodiment of this application, the first cathode material and the second cathode material each independently include a dopant element, which includes at least one selected from aluminum, magnesium, titanium, tungsten, zirconium, iridium, molybdenum, or vanadium; based on the mass of the first cathode material, the molar percentage W1 of the dopant element in the first cathode material is 0.5% to 5%. In one embodiment of this application, 1% ≤ W1 ≤ 3%. For example, W1 can be 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.5%, 4%, 4.5%, 5%, or a range consisting of any two of these values. In one embodiment of this application, based on the mass of the second cathode material, the molar percentage W2 of the dopant element in the second cathode material is 0.1% to 3%. In one embodiment of this application, 0.5% ≤ W2 ≤ 1%. For example, W2 can be 0.1%, 0.2%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.5%, 2%, 2.5%, 3%, or a range of any two values ​​therein. The doping elements of the first and second cathode materials are selected from the above ranges, and controlling the molar percentage content within the scope of this application is beneficial to improving the structural stability of the first and second cathode materials, reducing the probability of side reactions, thereby reducing gas generation during the charging and discharging process of the secondary battery, and further improving the internal gas generation of the secondary battery.

[0037] In one embodiment of this application, the first material layer includes a first adhesive and a second adhesive, and the second material layer includes a third adhesive; the first adhesive and the third adhesive each independently include at least one of polyvinylidene fluoride, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyamide-imide, and styrene-butadiene rubber; the second adhesive includes at least one of polyacrylic acid and sulfonated polymer, wherein the sulfonated polymer includes at least one of perfluorosulfonic acid resin, sulfonated polyether ether ketone, sulfonated polystyrene, sulfonated polyimide, and sulfonated polyarylene ether sulfone. The first binder, second binder, and third binder are selected from the above-mentioned materials. The second binder is acidic and, when combined with the high-nickel content first material layer, it helps to neutralize the residual alkali generated in the first material layer during the preparation process, thereby reducing the overall residual alkali content of the positive electrode material layer. This helps to reduce gas generation during the charging and discharging process of the secondary battery. At the same time, it works synergistically with the first and third binders to improve the adhesion between the overall positive electrode material layer and the positive electrode current collector, improve the internal resistance of the secondary battery, and thus help to improve the cycle performance of the secondary battery.

[0038] In one embodiment of this application, the mass percentage W of the first adhesive is based on the mass of the first material layer. N1 The mass percentage of the second adhesive W N2 0.5% ≤ W N1 +W N2 ≤2.5%, 0.3%≤W N2 ≤1.5%. For example, W N1 +W N2 The value can be 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, or a range of any two of these values; the mass percentage W of the second adhesive. N2 It can be 0.3%, 0.5%, 0.7%, 0.9%, 1%, 1.2%, 1.5%, or a range of any two of these values. This is achieved by adjusting W... N1 +W N2 value, W N2 Within the scope of this application, the acidic second binder is beneficial for neutralizing the residual alkali generated by the first positive electrode material during the preparation of the positive electrode sheet, reducing the probability of excessive gas generation during the charging and discharging of the secondary battery due to the high residual alkali content, further improving the internal gas generation of the secondary battery, and working synergistically with the first binder to improve the adhesion between the first material layer, the second binder layer, and the positive electrode current collector, further improving the cycle performance of the secondary battery while taking into account the energy density.

[0039] In one embodiment of this application, the mass percentage W of the third adhesive is based on the mass of the second material layer.N3 It ranges from 0.5% to 2.5%. For example, W N3 The value can be 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, or a range of any two of these values. This is achieved by adjusting W... N3 Within the scope of this application, the value of the third binder, together with the first and second binders, works synergistically to improve the adhesion between the overall positive electrode material layer and the positive electrode current collector, thereby further improving the cycle performance of the secondary battery while also taking into account the energy density.

[0040] In one embodiment of this application, the mass percentage of the first positive electrode material is greater than or equal to 85% based on the mass of the first material layer. In another embodiment, the mass percentage of the first positive electrode material is greater than or equal to 85% and less than or equal to 97.4% based on the mass of the first material layer. For example, the mass percentage of the first positive electrode material can be 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 97.4%, or a range of any two of these values. By controlling the mass percentage of the first positive electrode material within the scope of this application, the first positive electrode material is the main material of the first material layer, and the first positive electrode material has a high nickel content, resulting in a secondary battery with a high energy density.

[0041] In one embodiment of this application, the mass percentage of the second positive electrode material is greater than or equal to 85% based on the mass of the second material layer. In another embodiment, the mass percentage of the second positive electrode material is greater than or equal to 85% and less than or equal to 97.4% based on the mass of the second material layer. For example, the mass percentage of the second positive electrode material can be 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 97.4%, or a range of any two of these values. By controlling the mass percentage of the second positive electrode material within the scope of this application, the second positive electrode material is the main material of the second material layer. The second material layer has more contact with air, and the second positive electrode material has a suitable nickel content, which helps to reduce the amount of residual alkali generated in the positive electrode material layer during the preparation process, and reduces gas production in the secondary battery during charging and discharging, thereby improving the internal gas production of the secondary battery while maintaining energy density.

[0042] In one embodiment of this application, the first cathode material and the second cathode material each independently comprise lithium nickel cobalt manganese oxide. When the first cathode material comprises lithium nickel cobalt manganese oxide and the lithium nickel cobalt manganese oxide does not contain the aforementioned doping elements, the chemical formula of the lithium nickel cobalt manganese oxide is Li. n11 Ni x11 Co y11 Mnz11 When O2 is present, 0.95≤n11≤1.05, x11+y11+z11=1, 0.7≤x11≤0.95, 0.01≤y11≤0.3, 0.01≤z11≤0.2;

[0043] When the second cathode material is lithium nickel cobalt manganese oxide and the lithium nickel cobalt manganese oxide does not contain the aforementioned doping elements, the chemical formula of lithium nickel cobalt manganese oxide is Li. n12 Ni x12 Co y12 Mn z12 When O2 is present, 0.95≤n12≤1.05, x12+y12+z12=1, 0.3≤x12≤0.5, 0.01≤y12≤0.5, 0.2≤z12≤0.4;

[0044] When the first cathode material is lithium nickel cobalt manganese oxide and the lithium nickel cobalt manganese oxide contains the aforementioned doping elements, the chemical formula of lithium nickel cobalt manganese oxide is Li. n21 Ni x21 Co y21 Mn z21 M21 m21 In O2, M21 is selected from at least one of aluminum, magnesium, titanium, tungsten, zirconium, iridium, molybdenum or vanadium, 0.95≤n21≤1.05, x21+y21+z21+m21=1, 0.7≤x21≤0.95, 0.01≤y21≤0.295, 0.01≤z21≤0.2, 0.005≤m21≤0.05;

[0045] When the second cathode material includes lithium nickel cobalt manganese oxide and the lithium nickel cobalt manganese oxide contains the aforementioned doping elements, the chemical formula of lithium nickel cobalt manganese oxide is Li. n22 Ni x22 Co y22 Mn z22 M22 m22 When O2 is present, M22 is selected from at least one of aluminum, magnesium, titanium, tungsten, zirconium, iridium, molybdenum or vanadium, 0.95≤n22≤1.05, x22+y22+z22+m22=1, 0.3≤x22≤0.5, 0.01≤y22≤0.499, 0.2≤z22≤0.4, 0.001≤m22≤0.03.

[0046] In some embodiments of this application, when lithium nickel cobalt manganese oxide does not contain the aforementioned doping elements, the first cathode material may include, but is not limited to, LiNi. 0.7 Co 0.15 Mn 0.15 O2, LiNi 0.7 Co 0.2 Mn 0.1 O2, LiNi 0.8 Co 0.1 Mn0.1 O2(NCM811), LiNi 0.85 Co 0.08 Mn 0.07 O2, LiNi 0.88 Co 0.06 Mn 0.06 O2, LiNi 0.9 Co 0.05 Mn 0.05 O2, LiNi 0.95 Co 0.03 Mn 0.02 At least one of O2, and the second cathode material may include, but is not limited to, LiNi. 0.3 Co 0.3 Mn 0.4 O2, LiNi 0.33 Co 0.33 Mn 0.33 O2(NCM111), LiNi 0.4 Co 0.4 Mn 0.2 O2, LiNi 0.5 Co 0.3 Mn 0.2 At least one of O2 (NCM532).

[0047] In some embodiments of this application, when lithium nickel cobalt manganese oxide contains the aforementioned doping elements, the first cathode material may include, but is not limited to, LiNi. 0.79 Co 0.1 Mn 0.1 Mg 0.01 O2, LiNi 0.795 Co 0.1 Mn 0.1 Mg 0.005 O2, LiNi 0.79 Co 0.1 Mn 0.1 Mg 0.01 O2, LiNi 0.77 Co 0.1 Mn 0.1 Mg 0.03 O2, LiNi 0.75 Co 0.1 Mn 0.1 Mg 0.05 O2, LiNi 0.79 Co 0.1 Mn 0.1 Al 0.01 At least one of O2, and the second cathode material may include, but is not limited to, LiNi. 0.339 Co 0.33 Mn 0.33 Al0.001 O2, LiNi 0.335 Co 0.33 Mn 0.33 Al 0.005 O2, LiNi 0.339 Co 0.33 Mn 0.33 Al 0.01 O2, LiNi 0.31 Co 0.33 Mn 0.33 Al 0.03 O2, LiNi 0.33 Co 0.33 Mn 0.33 Mg 0.01 At least one of O2.

[0048] In some embodiments of this application, the first material layer may further include a first conductive agent, wherein the mass percentage of the first conductive agent in the first material layer is 0.1% to 12.5%; the second material layer may further include a second conductive agent, wherein the mass percentage of the second conductive agent in the second material layer is 0.1% to 12.5%. For example, the mass percentage of the first conductive agent may be 0.1%, 1%, 2%, 4%, 6%, 8%, 10%, 12%, 12.5%, or a range consisting of any two of these values; the mass percentage of the second conductive agent may be 0.1%, 1%, 2%, 4%, 6%, 8%, 10%, 12%, 12.5%, or a range consisting of any two of these values.

[0049] In some embodiments of this application, there are no particular limitations on the types of the first and second conductive agents, as long as they can achieve the purpose of this application. For example, the first and second conductive agents can each independently include, but are not limited to, at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, graphene, metallic materials, or conductive polymers. Conductive carbon black can include, but is not limited to, at least one of acetylene black or Ketjen black. The aforementioned carbon nanotubes can include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The aforementioned carbon fibers can include, but are not limited to, vapor-grown carbon fibers (VGCF) and / or carbon nanofibers. The aforementioned metallic materials can include, but are not limited to, metal powders and / or metal fibers; specifically, the metal can include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The aforementioned conductive polymers can include, but are not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole.

[0050] This application does not impose any particular restrictions on the preparation method of the positive electrode sheet, as long as it can achieve the purpose of this application. For example, the preparation method of the positive electrode sheet can be as follows: (1) Mix the first positive electrode material, the first conductive agent, the first binder, and the second binder, add a solvent, adjust to form a slurry, stir evenly, and obtain a first material layer slurry; (2) Mix the second positive electrode material, the second conductive agent, and the third binder, add a solvent, adjust to form a slurry, stir evenly, and obtain a second material layer slurry; (3) Coat the first material layer slurry evenly on one surface of the positive electrode current collector, dry it, and then coat the second material layer slurry evenly on one surface of the first material layer away from the positive electrode current collector, dry it, and obtain a positive electrode sheet with a single-sided coating of the first material layer and the second material layer; (4) Repeat the above coating process on the other surface of the positive electrode current collector and dry it to obtain a positive electrode sheet with a double-sided coating of the first material layer and the second material layer.

[0051] In this application, the first cathode material and the second cathode material with different nickel contents can be purchased, and their nickel contents can be tested by inductively coupled plasma mass spectrometry to select the first cathode material and the second cathode material with the required nickel contents.

[0052] In this application, the first cathode material and the second cathode material with different types and contents of doped elements can be purchased, and their types and contents of doped elements can be tested by inductively coupled plasma mass spectrometry, so that the first cathode material and the second cathode material with the required types and contents of doped elements can be selected.

[0053] In this application, the positive electrode includes a positive current collector and a first material layer and a second material layer disposed on the surface of the positive current collector. The aforementioned "first material layer and second material layer disposed on the surface of the positive current collector" means that the first material layer and the second material layer can be disposed on one surface of the positive current collector along its thickness direction, or on both surfaces of the positive current collector along its thickness direction. It should be noted that the "surface" here can be the entire surface area of ​​the positive current collector, or it can be a partial surface area; this application has no particular limitation, as long as the purpose of this application is achieved.

[0054] This application does not impose any particular restrictions on the positive electrode current collector, as long as it can achieve the purpose of this application. For example, it may include aluminum foil, aluminum alloy foil, or composite current collector (such as aluminum-carbon composite current collector).

[0055] This application does not impose any particular limitation on the thickness of the positive electrode current collector, as long as it achieves the purpose of this application. For example, the thickness of the positive electrode current collector can be from 8 μm to 20 μm.

[0056] In this application, the total thickness of the first material layer and the second material layer can be from 30 μm to 150 μm.

[0057] In this application, the secondary battery also includes a separator. This application does not impose any particular limitation on the separator, as long as it achieves the purpose of this application. For example, the separator material may include, but is not limited to, at least one of polyethylene (PE), polyolefins (PO) primarily composed of polypropylene (PP), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid. The separator type may include at least one of woven membrane, nonwoven membrane, microporous membrane, composite membrane, rolled membrane, or spun membrane.

[0058] In some embodiments of this application, the diaphragm may include a substrate layer and a surface treatment layer. The substrate layer may be a nonwoven fabric or composite membrane with a porous structure, and the material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be used.

[0059] Optionally, a surface treatment layer is provided on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing polymers and inorganic substances.

[0060] In some embodiments of this application, the inorganic layer comprises inorganic particles and an inorganic layer binder. This application does not particularly limit the inorganic particles; for example, the inorganic particles may include at least one selected from alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. This application also does not particularly limit the inorganic layer binder; for example, the inorganic layer binder may be at least one of the negative electrode binders. In some embodiments of this application, the polymer layer comprises a polymer, and the polymer material includes at least one selected from polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, or polyvinylidene fluoride or poly(vinylidene fluoride-hexafluoropropylene).

[0061] In this application, there is no particular limitation on the thickness of the diaphragm, as long as it can achieve the purpose of this application. For example, the thickness of the diaphragm can be from 3 μm to 30 μm.

[0062] In this application, the negative electrode sheet includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector. The phrase "the negative electrode material layer is disposed on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be disposed on one surface of the negative electrode current collector along its thickness direction, or on two surfaces of the negative electrode current collector along its thickness direction. It should be noted that the term "surface" here can refer to the entire surface area of ​​the negative electrode current collector, or only a portion thereof; this application does not impose any particular limitation, as long as the purpose of this application is achieved.

[0063] This application does not impose any particular restrictions on the negative electrode current collector, as long as it can achieve the purpose of this application. For example, it may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or composite current collector. For example, the composite current collector may be lithium copper composite current collector, carbon copper composite current collector, nickel copper composite current collector, titanium copper composite current collector, etc.

[0064] The negative electrode material layer includes a negative electrode active material. This application does not impose any particular limitation on the negative electrode active material, as long as it can achieve the purpose of this application. For example, the negative electrode active material may include, but is not limited to, natural graphite, artificial graphite, mesophase micro carbon spheres, hard carbon, soft carbon, silicon, silicon-carbon composites, Li-Sn alloys, Li-Sn-O alloys, Sn, SnO, SnO2, and spinel-structured lithiated TiO2-Li4Ti5O. 12 Or at least one of Li-Al alloys.

[0065] In some embodiments of this application, the negative electrode material layer may further include a negative electrode conductive agent and a negative electrode binder. This application does not particularly limit the types of negative electrode conductive agents and negative electrode binders, as long as they achieve the purpose of this application. For example, the negative electrode conductive agent may include, but is not limited to, at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, graphene, metallic materials, or conductive polymers. The conductive carbon black may include, but is not limited to, at least one of acetylene black or Ketjen black. The aforementioned carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The aforementioned carbon fibers may include, but are not limited to, vapor-grown carbon fibers (VGCF) and / or carbon nanofibers. The aforementioned metallic materials may include, but are not limited to, metal powders and / or metal fibers; specifically, the metal may include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The aforementioned conductive polymer may include, but is not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole. For example, the negative electrode binder may include, but is not limited to, at least one of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyimide, polyamide-imide, styrene-butadiene rubber, or polyvinylidene fluoride. This application does not impose any particular limitation on the mass ratio of the negative electrode active material, the negative electrode conductive agent, and the negative electrode binder in the negative electrode material layer; those skilled in the art can select according to actual needs, as long as the purpose of this application is achieved.

[0066] This application does not impose any particular limitation on the thickness of the negative electrode material layer, as long as it can achieve the purpose of this application. For example, the thickness of the negative electrode material layer is 30 μm to 120 μm.

[0067] This application does not impose any particular limitation on the thickness of the negative electrode current collector, as long as it can achieve the purpose of this application. For example, the thickness of the negative electrode current collector is 4 μm to 15 μm.

[0068] Optionally, the negative electrode sheet may further include a negative electrode conductive layer, which is located between the negative electrode current collector and the negative electrode material layer. This application does not impose any particular limitation on the composition of the negative electrode conductive layer, and it can be a conductive layer commonly used in the art. For example, the negative electrode conductive layer includes a negative electrode conductive agent and a negative electrode conductive layer binder. This application does not impose any particular limitation on the negative electrode conductive agent and the negative electrode conductive layer binder; for example, it can be at least one of the aforementioned negative electrode conductive agent and negative electrode binder.

[0069] In this application, the electrolyte includes lithium salts and non-aqueous solvents.

[0070] This application does not impose any particular limitation on the lithium salt, as long as it achieves the purpose of this application. For example, the lithium salt may include, but is not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium perchlorate (LiClO4), lithium tetraphenylboron (LiB(C6H5)4), lithium methanesulfonate (LiCH3SO3), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(trifluoromethanesulfonyl)imide (LiN(SO2CF3)2), lithium tris(trifluoromethanesulfonyl)methyl (LiC(SO2CF3)3), lithium hexafluorosilicate (LiSiF6), lithium bis(oxalato)borate (LiBOB), and lithium difluoroborate (LiF2OB). This application does not impose any particular limitation on the content of the lithium salt in the electrolyte, as long as it achieves the purpose of this application. For example, based on the mass of the electrolyte, the mass percentage of the lithium salt may be 8% to 15%. For example, the mass percentage of lithium salt can be 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, or a range of any two of these values.

[0071] This application does not impose any particular restrictions on non-aqueous solvents, as long as they can achieve the purpose of this application. For example, non-aqueous solvents may include, but are not limited to, at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, or other organic solvents.

[0072] The aforementioned carbonate compounds may include, but are not limited to, at least one of chain carbonate compounds, cyclic carbonate compounds, or fluorocarbonate compounds. The aforementioned chain carbonate compounds may include, but are not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or methyl ethyl carbonate (MEC). The aforementioned cyclic carbonates may include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), or vinyl ethylene carbonate (VEC). Fluorocarbonate compounds may include, but are not limited to, at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethylethylene carbonate. The aforementioned carboxylic acid ester compounds may include, but are not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valproic acid lactone, or caprolactone. The aforementioned ether compounds may include, but are not limited to, at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. The aforementioned other organic solvents may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate.

[0073] This application does not impose any particular limitation on the content of non-aqueous solvents in the electrolyte, as long as the purpose of this application is achieved. For example, based on the mass of the electrolyte, the mass percentage of non-aqueous solvents can be 70% to 85%. For example, the mass percentage of non-aqueous solvents can be 70%, 72%, 74%, 76%, 78%, 80%, 82%, 84%, 85%, or a range of any two of these values.

[0074] The secondary battery also includes a casing for housing the positive electrode, separator, negative electrode, and electrolyte, as well as other components known in the field of secondary batteries. This application does not limit the scope of these other components. This application does not impose any particular limitation on the casing; it can be a casing known in the art, as long as it achieves the purpose of this application. For example, the casing can be a rigid casing or a flexible casing. The material of the rigid casing can be metal; this application does not limit the type of metal and can use known metal rigid casings, as long as they achieve the purpose of this application. The flexible casing can be a metal plastic film, such as aluminum-plastic film, steel-plastic film, etc.

[0075] The fabrication process of the secondary battery described in this application is well known to those skilled in the art, and this application does not impose any particular limitations. For example, the fabrication process of the secondary battery may include, but is not limited to, the following steps: stacking the positive electrode, separator, and negative electrode in sequence, and performing operations such as winding and folding as needed to obtain a wound electrode assembly; placing the electrode assembly into a housing; injecting electrolyte into the housing and sealing it to obtain the secondary battery. Alternatively, stacking the positive electrode, separator, and negative electrode in sequence, and then fixing the four corners of the entire stacked structure with tape to obtain a stacked electrode assembly; placing the electrode assembly into a housing; injecting electrolyte into the housing and sealing it to obtain the secondary battery. In addition, overcurrent protection elements, conductive plates, etc., may be placed in the housing as needed to prevent pressure rise and overcharging / discharging inside the secondary battery.

[0076] In some embodiments of this application, the secondary battery may include, but is not limited to, lithium metal secondary batteries, lithium-ion secondary batteries (lithium-ion batteries), lithium polymer secondary batteries, or lithium-ion polymer secondary batteries. In some embodiments of this application, the secondary battery includes lithium-ion batteries.

[0077] A second aspect of this application provides an electronic device comprising the secondary battery described in the first aspect of this application.

[0078] This application does not specifically limit the type of electronic device; it can be any electronic device known in the prior art. In some embodiments of this application, the electronic device may include, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.

[0079] Example

[0080] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0081] Test methods and equipment:

[0082] sampling:

[0083] The lithium-ion battery was disassembled at an ambient temperature of 25°C, the positive electrode was removed, cleaned with dimethyl carbonate, and then placed in an oven and dried at 80°C for 12 hours to obtain a positive electrode sample.

[0084] Unless otherwise specified, the above samples were used for testing.

[0085] Test on the types and mass percentage of additives in the electrolyte:

[0086] First, discharge the lithium-ion battery to 3V at a constant current of 0.5C under 25℃ conditions. Then, remove the packaging bag, cut off the tabs, wind up the remaining electrode assembly and put it into a centrifuge tube. Let it stand to collect the electrolyte sample, centrifuge the electrolyte sample in a centrifuge, and take the supernatant as the test sample.

[0087] The types and contents of additives in the electrolyte test sample were determined using gas chromatography-mass spectrometry (GC-MS), with the types of additives being determined by comparison with standard cards.

[0088] Test of the molar percentage of nickel and doping elements in the first and second cathode materials:

[0089] The cross-section of the positive electrode sheet along its thickness direction was ion-polished. The resulting cross-section was then observed using a scanning electron microscope (SEM) combined with energy dispersive spectroscopy (EDS). The layer with the higher nickel content was identified as the first material layer, and the layer with the lower nickel content as the second material layer. The types of doping elements were then determined based on the SEM and EDS observations.

[0090] The first material layer is located between the positive electrode current collector and the second material layer. The thickness of the first material layer is measured and recorded as h1, and the thickness of the second material layer is recorded as h2. Based on the measured thickness, the positive electrode material layer with a thickness less than h2 is scraped off, and the resulting powder is used as the second material layer powder. Then, the positive electrode material layer with a thickness greater than h2 is scraped off, and the positive electrode material layer is scraped off again, and the resulting powder is used as the first material layer powder.

[0091] The powder of the first material layer was calcined at 600℃ in a nitrogen atmosphere for 2 hours to obtain the first cathode material sample. Then, 0.4g of the sample was dissolved in 10mL of aqua regia (concentrated hydrochloric acid (HCl) and concentrated nitric acid (HNO3) in a volume ratio of 3:1), dissolved at 180℃ for 30min, cooled to room temperature, and the sample was brought to a final volume of 100mL.

[0092] Standard curves: A series of nickel, cobalt, manganese, and dopant element standard solutions of different concentrations were prepared. The mass numbers of the standard solutions were measured using inductively coupled plasma mass spectrometry (ICP-MS), and standard curves for nickel, cobalt, manganese, and dopant elements were plotted. When the type and number of dopant elements can be confirmed using EDS, the number of standard curves for each dopant element corresponds to the number of dopant element types.

[0093] Sample testing: The prepared sample solution was introduced into an ICP-MS instrument to measure the content of nickel, cobalt, manganese, and dopant elements. Based on the standard curve, the mass concentrations of nickel, cobalt, manganese, and dopant elements were obtained, and their masses were calculated. This yielded the molar numbers n1 (nickel), n2 (cobalt), n3 (manganese), and n4 (dopant elements). The sum of these molar numbers was taken as the total number of moles of non-lithium metal elements.

[0094] The molar percentage of nickel in the first cathode material is N1 (%) = n1 / (n1+n2+n3+n4)×100%; the molar percentage of doped elements in the first cathode material is W1 (%) = n4 / (n1+n2+n3+n4)×100%.

[0095] By replacing the powder of the first material layer with the powder of the second material layer, and following the steps described above, the molar percentage of nickel in the second cathode material N2 and the molar percentage of doped elements in the second cathode material W2 can be obtained.

[0096] Method for testing thickness expansion rate during 6 hours of storage at 80℃:

[0097] The lithium-ion battery was charged at a constant current rate of 0.5C to 4.4V, and then charged at a constant voltage rate to 0.05C. The lithium-ion battery was placed at 80℃ for 6 hours. The thickness of the lithium-ion battery before and after high-temperature storage was measured using a flat plate thickness gauge with a 1000g counterweight, H0 and H1 respectively. The thickness expansion rate (%) of the battery after 6 hours of storage at 80℃ was calculated as (H1-H0) / H0×100%.

[0098] Volumetric energy density test:

[0099] At 25℃, the lithium-ion battery was charged at a constant current of 0.5C to 4.4V, then charged at a constant voltage of 0.05C and allowed to stand for 5 minutes; then discharged at a constant current of 0.2C to 3.0V and allowed to stand for 5 minutes. The discharge energy at this point is recorded as the energy of the lithium-ion battery (Wh); the length, width, and height of the lithium-ion battery are measured, and its volume (L) is calculated. The energy density of the lithium-ion battery (Wh / L) is calculated using the following formula: Energy of lithium-ion battery (Wh) / Volume of lithium-ion battery (L).

[0100] 45℃ 600-cycle capacity retention test:

[0101] At 45℃, the lithium-ion battery was charged at a constant current rate of 0.5C to 4.4V, then charged at a constant voltage rate to 0.05C, and then discharged at 0.5C to 3.0V, completing one cycle, which is recorded as the first cycle. The discharge capacity of the first cycle was recorded, and the battery was allowed to stand for 5 minutes. Then, the above steps were repeated for 600 cycles, and the discharge capacity after each cycle was recorded.

[0102] Capacity retention rate (%) = (Discharge capacity after 600 cycles / Discharge capacity in the first cycle) × 100%.

[0103] Example 1-1

[0104] <Preparation of the positive electrode>

[0105] (1) The first positive electrode material NCM811, the first conductive agent acetylene black, and the first binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 97:2:1. N-methylpyrrolidone (NMP) is added as a solvent to prepare a slurry with a solid content of 75wt%. After vacuum stirring, the first material layer slurry is obtained.

[0106] (2) The second positive electrode material NCM111, the second conductive agent acetylene black, and the third binder PVDF are mixed in a mass ratio of 97:2:1. NMP is added as a solvent to prepare a slurry with a solid content of 75wt%. After vacuum stirring, the second material layer slurry is obtained.

[0107] (3) The first material layer slurry is uniformly coated on one surface of a 10 μm thick positive electrode current collector aluminum foil and dried at 120°C. Then, the second material layer slurry is uniformly coated on the surface of the first material layer away from the positive electrode current collector, resulting in a positive electrode sheet with a single-sided coating of the first and second material layers. The coating mass CW1 of the first material layer is 200 mg / 1540.24 mm. 2 The coating mass per unit area of ​​the second material layer, CW2, is 50 mg / 1540.24 mm. 2The value of CW1+CW2 was 250mg / 1540.24mm. 2 The above steps are then repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of the first and second material layers. After drying at 120℃, it is cold-pressed, then cut and welded with tabs to obtain a positive electrode sheet with dimensions of 74mm × 867mm for later use. The overall compaction density of the first and second material layers is 4.23 g / cm³. 3 .

[0108] <Preparation of Negative Electrode Sheets>

[0109] Artificial graphite (negative electrode active material), styrene-butadiene rubber (negative electrode binder), and acetylene black (negative electrode conductive agent) were mixed in a mass ratio of 97.4:1.4:1.2. Deionized water was added as a solvent to prepare a slurry with a solid content of 45 wt%. The slurry was stirred evenly in a vacuum mixer to obtain the negative electrode slurry. The negative electrode slurry was uniformly coated onto one surface of a 6 μm thick copper foil current collector and dried at 120 °C to obtain a negative electrode sheet with a single-sided negative electrode material layer. The coating weight of the negative electrode material layer was 142 mg / 1540.24 mm. 2 The above steps are then repeated on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided coating of negative electrode material. After drying at 120℃ and cold pressing, the sheet is cut and tabs are welded to obtain a negative electrode sheet with dimensions of 78mm × 875mm for later use. The thickness of the single-sided negative electrode material layer is 54.5μm, and the compaction density of the negative electrode material layer is 1.735g / cm³. 3 .

[0110] <Preparation of Electrolyte>

[0111] In an environment with a water content of less than 10 ppm, dimethyl carbonate, diethyl carbonate, and ethylene carbonate are mixed in a mass ratio of 1:1:1 to obtain a non-aqueous solvent. Then, the electrolyte salt LiPF6 and ethyl fluorocarbonate are added to the non-aqueous solvent and mixed thoroughly to obtain the electrolyte. Based on the mass of the electrolyte, the electrolyte salt comprises 12.5% ​​by mass, the ethyl fluorocarbonate comprises 5% by mass, and the remainder is the non-aqueous solvent.

[0112] <Septum>

[0113] A porous polyethylene film with a thickness of 7μm (provided by Celgard) was used as the separator.

[0114] <Preparation of Lithium-ion Batteries>

[0115] The prepared positive electrode, separator, and negative electrode are stacked sequentially, with the separator positioned between the positive and negative electrodes to provide insulation. The electrode assembly is then wound to obtain the electrode assembly. This assembly is placed in an aluminum-plastic film casing and dehydrated at 80°C. The prepared electrolyte is then injected, followed by vacuum sealing, settling, formation, degassing, and edge trimming to obtain a lithium-ion battery. The formation upper limit voltage is 4.2V, the formation temperature is 70°C, and the formation settling time is 2 hours.

[0116] Examples 1-2 to Examples 1-6

[0117] Except for adjusting the mass percentage of additives in the electrolyte according to Table 1, changing the mass percentage of non-aqueous solvents accordingly, and keeping the mass percentage of lithium salts unchanged, everything else is the same as in Examples 1-1.

[0118] Examples 1-7 to Examples 1-23

[0119] Except for adjusting the relevant parameters according to Table 1, everything else is the same as in Example 1-1.

[0120] Examples 2-1 to 2-4, Examples 2-10 to 2-13

[0121] Except for adjusting the relevant parameters according to Table 2, the rest is the same as in Example 1-1. When the mass percentage of the third binder changes, the mass percentage of the second positive electrode material changes accordingly, while the mass percentage of the second conductive agent remains unchanged.

[0122] Examples 2-5

[0123] Except for preparing the slurry for the first material layer in the positive electrode according to the following steps, the rest is the same as in Example 1-1.

[0124] <Preparation of the First Material Layer Slurry>

[0125] The first positive electrode material NCM811, the first conductive agent acetylene black, the first binder PVDF, and the second binder polyacrylic acid were mixed in a mass ratio of 96.5:2:0.5:1. NMP was added as a solvent to prepare a slurry with a solid content of 75wt%. After vacuum stirring, the first material layer slurry was obtained.

[0126] Examples 2-6 to 2-9

[0127] Except for adjusting the relevant parameters according to Table 2, the rest is the same as in Examples 2-5. When the mass percentage content of the first binder and the second binder changes, the mass percentage content of the first positive electrode material changes accordingly, while the mass percentage content of the first conductive agent remains unchanged.

[0128] Examples 3-1 to 3-9

[0129] Except for adjusting the relevant parameters according to Table 3, the rest is the same as in Example 1-1.

[0130] Comparative Example 1

[0131] Except that the electrolyte does not contain additives, the mass percentage of non-aqueous solvents changes accordingly, and the mass percentage of lithium salt remains unchanged, everything else is the same as in Example 1-1.

[0132] Comparative Examples 2 to 3

[0133] Except for adjusting the mass percentage of additives in the electrolysis to be as shown in Table 1, changing the mass percentage of non-aqueous solvents accordingly, and keeping the mass percentage of lithium salts unchanged, everything else is the same as in Examples 1-1.

[0134] Comparative Examples 4 to 6

[0135] Except for adjusting the relevant parameters according to Table 1, everything else is the same as in Example 1-1.

[0136] The preparation and performance parameters of each embodiment and comparative example are shown in Tables 1 to 3.

[0137] Table 1 Note: In Table 1, " / " indicates that there is no corresponding preparation parameter, substance, or performance parameter.

[0138] Table 2 Note: In Table 2, " / " indicates that there is no corresponding preparation parameter, substance, or performance parameter.

[0139] As can be seen from Examples 1-1 to 1-23 and Comparative Examples 1 to 6, when the molar percentage of nickel in the first cathode material N1 is greater than the molar percentage of nickel in the second cathode material N2, and the type and mass percentage of additives in the electrolyte are within the scope of this application, the resulting lithium-ion battery exhibits a lower thickness expansion rate at 80°C for 6 hours, a higher volumetric energy density, and a higher capacity retention rate after 600 cycles at 45°C. This demonstrates that the lithium-ion battery obtained in this application can balance internal gas generation and energy density. Specifically, in Comparative Examples 1 and 2, because the mass percentage of additives in the electrolyte is lower than the scope of this application, the resulting lithium-ion batteries exhibit a higher thickness expansion rate at 80°C for 6 hours and a lower capacity retention rate after 600 cycles at 45°C. In Comparative Example 3, because the additive content in the electrolyte is too high, although the resulting lithium-ion battery has a lower thickness expansion rate at 80°C for 6 hours, both the capacity retention rate and energy density after 600 cycles at 45°C are lower. In Comparative Example 4, because N2 is higher than the scope of this application and N1 is equal to N2, the resulting lithium-ion battery has a higher energy density. However, the thickness expansion rate after 6 hours of storage at 80℃ was relatively high, and the capacity retention rate after 600 cycles at 45℃ was relatively low. In Comparative Example 5, because N1 was below the scope of this application and N1 was equal to N2, the resulting lithium-ion battery had a low thickness expansion rate after 6 hours of storage at 80℃ and a high capacity retention rate after 600 cycles at 45℃, but a low energy density. In Comparative Example 6, because N1 and N2 were not within the scope of this application and N1 was less than N2, the resulting lithium-ion battery had a high thickness expansion rate after 6 hours of storage at 80℃, a low capacity retention rate after 600 cycles at 45℃, and a low energy density. It is evident that the lithium-ion batteries in Comparative Examples 1 to 6 struggle to balance internal gas generation and energy density.

[0140] As can be seen from Examples 1-1 to 1-6, when the mass percentage W of the additive in the electrolyte is within the range of this application, the resulting lithium-ion battery exhibits low thickness expansion rate, high volumetric energy density, and high capacity retention rate after 600 cycles at 45°C, demonstrating that the lithium-ion battery obtained in this application can balance internal gas generation and energy density. Furthermore, when 3% ≤ W ≤ 10%, it can further balance internal gas generation and energy density.

[0141] The molar percentage of nickel in the first cathode material (N1) and the molar percentage of nickel in the second cathode material (N2) affect the internal gas generation and energy density of the secondary battery. As can be seen from Examples 1-1, 1-9 to 1-13, and 1-14 to 1-18, when the molar percentages of nickel in the first cathode material (N1) and the second cathode material (N2) are within the scope of this application, the resulting lithium-ion battery exhibits lower thickness expansion rate, higher volumetric energy density, and higher capacity retention rate after 600 cycles at 80°C, demonstrating that the lithium-ion battery obtained in this application can improve energy density while also addressing internal gas generation.

[0142] As can be seen from Examples 1-1, 1-19 to 1-23, when the values ​​of CW1 / (CW1+CW2) and CW2 / (CW1+CW2) are within the range of this application, the resulting lithium-ion battery has a low thickness expansion rate, high volumetric energy density, and high capacity retention rate after 600 cycles at 80°C. This indicates that the lithium-ion battery obtained in this application can balance internal gas generation and energy density.

[0143] As can be seen from Examples 1-1, 2-1 to 2-4, when the value of CW1+CW2 is within the range of this application, the resulting lithium-ion battery has a low thickness expansion rate, high volumetric energy density, and high capacity retention rate after 600 cycles at 80°C, thus indicating that the lithium-ion battery obtained in this application can balance internal gas generation and energy density.

[0144] As can be seen from Examples 1-1, 2-5 to 2-9, when the first material layer contains the second binder, the thickness expansion rate of the lithium-ion battery at 80°C for 6 hours is improved, and the volumetric energy density is high and the capacity retention rate at 45°C for 600 cycles is high, indicating that the lithium-ion battery obtained in this application can balance internal gas generation and energy density.

[0145] As can be seen from Examples 2-5 to Examples 2-9, when the type and mass percentage of the second binder are within the scope of this application, the resulting lithium-ion battery has a low thickness expansion rate, high volumetric energy density, and high capacity retention rate after 600 cycles at 45°C, which indicates that the lithium-ion battery obtained in this application can improve internal gas generation while maintaining energy density.

[0146] As can be seen from Examples 1-1, 2-11 to 2-13, when the type and mass percentage of the third binder are within the range of this application, the resulting lithium-ion battery has a low thickness expansion rate, high volumetric energy density, and high capacity retention rate after 600 cycles at 45°C, which shows that the lithium-ion battery obtained in this application can improve internal gas generation while taking into account energy density.

[0147] Table 3 Note: In Table 3, " / " indicates that there is no corresponding preparation parameter, substance, or performance parameter.

[0148] As can be seen from Examples 1-1, 3-1 to 3-9, when the first cathode material and the second cathode material contain doped elements, the thickness expansion rate of the lithium-ion battery is improved during storage at 80°C for 6 hours, and the volumetric energy density is high, and the capacity retention rate after 600 cycles at 45°C is high. This shows that the lithium-ion battery obtained in this application can improve internal gas generation while maintaining energy density.

[0149] As can be seen from Examples 3-1 to 3-9, when the types and mass percentages of doped elements in the first cathode material and the second cathode material are within the range of this application, the resulting lithium-ion battery has a low thickness expansion rate, high volumetric energy density, and high capacity retention rate after 600 cycles at 45°C, which indicates that the lithium-ion battery obtained in this application can improve internal gas generation while maintaining energy density.

[0150] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, or article that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, or article.

[0151] The various embodiments in this specification are described in a related manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0152] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A secondary battery, comprising a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode comprises a positive current collector and a first material layer and a second material layer disposed on the surface of the positive current collector, the first material layer being located between the positive current collector and the second material layer; The first material layer includes a first positive electrode material, which includes nickel, cobalt and manganese. Based on the total number of moles of non-lithium metal elements in the first positive electrode material, the molar percentage of nickel in the first positive electrode material is N1. The second material layer includes a second positive electrode material, which includes nickel, cobalt and manganese. Based on the total number of moles of non-lithium metal elements in the second positive electrode material, the molar percentage of nickel in the second positive electrode material is N2. N1 > N2; The electrolyte includes additives, which include at least one of carboxylic acid esters, fluorocarboxylic acid esters, ethyl propionate, propyl propionate, ethyl fluoroacetate, vinyl sulfate, and bicyclic sulfate. The mass percentage W of the additives is 1% to 20% based on the mass of the electrolyte.

2. The secondary battery according to claim 1, wherein, 70% ≤ N1 ≤ 95%, 30% ≤ N2 ≤ 50%.

3. The secondary battery according to claim 2, wherein, 80% ≤ N1 ≤ 90%, and / or, 33% ≤ N2 ≤ 40%.

4. The secondary battery according to claim 1, wherein, The additives include at least one of ethyl fluoroacetate and vinyl sulfate.

5. The secondary battery according to claim 1, wherein, 3％≤W≤10％。 6. The secondary battery according to any one of claims 1 to 5, wherein, The coating mass per unit area of ​​the first material layer is CW1, and the coating mass per unit area of ​​the second material layer is CW2, with 50% ≤ CW1 / (CW1+CW2)×100% ≤ 90% and 10% ≤ CW2 / (CW1+CW2)×100% ≤ 50%.

7. The secondary battery according to claim 6, wherein, 70% ≤ CW1 / (CW1+CW2)×100% ≤ 80%, and / or, 10% ≤ CW2 / (CW1+CW2)×100% ≤ 30%.

8. The secondary battery according to claim 6, wherein, 150mg / 1540.24mm 2 ≤CW1+CW2≤350mg / 1540.24mm 2 。 9. The secondary battery according to claim 8, wherein, 200mg / 1540.24mm 2 ≤CW1+CW2≤300mg / 1540.24mm 2 。 10. The secondary battery according to any one of claims 1 to 5, wherein, The first cathode material and the second cathode material each independently include a doping element, and the doping element includes at least one of aluminum, magnesium, titanium, tungsten, zirconium, iridium, molybdenum or vanadium; Based on the mass of the first cathode material, the molar percentage content W1 of the doping element in the first cathode material is 0.5% to 5%; Based on the mass of the second cathode material, the molar percentage W2 of the dopant element in the second cathode material is 0.1% to 3%.

11. The secondary battery according to claim 10, wherein, 1% ≤ W1 ≤ 3%, and / or, 0.5% ≤ W2 ≤ 1%.

12. The secondary battery according to any one of claims 1 to 5, wherein, The first material layer includes a first adhesive and a second adhesive, and the second material layer includes a third adhesive; The first adhesive and the third adhesive each independently comprise at least one of polyvinylidene fluoride, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyamide-imide, and styrene-butadiene rubber; The second adhesive comprises at least one of polyacrylic acid and a sulfonated polymer, wherein the sulfonated polymer comprises at least one of perfluorosulfonic acid resin, sulfonated polyether ether ketone, sulfonated polystyrene, sulfonated polyimide, and sulfonated polyarylether sulfone.

13. The secondary battery according to claim 12, wherein, Based on the mass of the first material layer, the mass percentage W of the first adhesive is... N1 The mass percentage of the second adhesive W N2 0.5% ≤ W N1 +W N2 ≤2.5%, 0.3%≤W N2 ≤1.5%; and / or, Based on the quality of the second material layer, the mass percentage W of the third adhesive N3 It ranges from 0.5% to 2.5%.

14. The secondary battery according to any one of claims 1 to 13, wherein it satisfies at least one of the following characteristics: (1) Based on the mass of the first material layer, the mass percentage of the first cathode material is greater than or equal to 85%; (2) Based on the mass of the second material layer, the mass percentage of the second cathode material is greater than or equal to 85%; (3) The first cathode material and the second cathode material each independently include lithium nickel cobalt manganese oxide.

15. An electronic device comprising a secondary battery as claimed in any one of claims 1 to 14.

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