Electrode assembly, electrochemical device and electric device

Abstract

An electrode assembly, an electrochemical device and an electric device. A positive electrode material layer of the electrode assembly comprises a first positive electrode material LiMnxFe1-xPO4; the single-sided thickness of the positive electrode material layer is T1 μm, and 22≤T1≤110; and the length of the positive electrode sheet is L1 mm. The electrode assembly further comprises at least one positive electrode tab, and when the number of the positive electrode tab is one, the positive electrode tab has a centrally-arranged electrode tab structure; or when the number of the positive electrode tabs is multiple, the ratio of the number of the positive electrode tabs to the L1 is B, and 0.002≤B≤0.01. By cooperatively regulating and controlling the type of the positive electrode material, the single-sided thickness of the positive electrode material layer and the structure of the positive electrode tab, the electrochemical device can have good discharge performance at low temperatures, thereby improving the experience of a user during the use of an electrochemical device product.

Description

An electrode assembly, an electrochemical device, and an electrical device.

[0001] This application claims priority to Chinese Patent Application No. 202310788604.6, filed on June 29, 2023, entitled "An Electrode Assembly, Electrochemical Device and Electrical 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 an electrode assembly, an electrochemical device, and an electrical device. Background Technology

[0003] Lithium-ion batteries possess numerous advantages, including high energy density, long cycle life, high nominal voltage, low self-discharge rate, small size, and light weight, making them widely used in portable electronic devices, electric bicycles, electric vehicles, and energy storage devices. Technicians are continuously improving the performance of lithium-ion batteries, ensuring their continued importance in the consumer electronics field for a long time to come.

[0004] Temperature is a crucial factor affecting the discharge performance of lithium-ion batteries during use. As the temperature decreases, both the discharge voltage and the State of Charge (SOC) of the lithium-ion battery decrease. Some existing products using lithium-ion batteries fail to meet the requirements for power-on and rapid discharge in low-temperature environments (e.g., temperatures below or equal to 10°C). Therefore, there is a need for a lithium-ion battery that can maintain good discharge performance under low-temperature conditions to improve the user experience when using lithium-ion battery products.

[0005] Summary of the Invention

[0006] The purpose of this application is to provide an electrode assembly, an electrochemical device, and an electrical device that exhibit good discharge performance under low-temperature conditions. The specific technical solution is as follows:

[0007] A first aspect of this application provides an electrode assembly comprising at least one positive electrode sheet, the positive electrode sheet comprising a positive current collector and a positive electrode material layer disposed on two surfaces of the positive current collector, wherein the positive electrode material layer comprises a first positive electrode material LiMn. x Fe 1-xPO4, 0≤x<0.95, the single-sided thickness of the positive electrode material layer is T1μm, 22≤T1≤110; the length of the positive electrode sheet is L1mm; the electrode assembly also includes at least one positive electrode tab. When the number of positive electrode tabs is one, the positive electrode tab is a centrally located structure; or, when the number of positive electrode tabs is multiple, the ratio of the number of positive electrode tabs to L1 is B, 0.002≤B≤0.01. By synergistically controlling the type of positive electrode material, the single-sided thickness of the positive electrode material layer, and the structure of the positive electrode tab, the electrochemical device can have good discharge performance at low temperatures, thereby improving the user experience during the use of the electrochemical device product.

[0008] In some embodiments of this application, when there are multiple positive electrode tabs, the ratio of the number of positive electrode tabs to T1 is A, where 0.05 ≤ A ≤ 0.1. By adjusting the value of A within the range of this application, the number of positive electrode tabs is matched with the single-sided thickness of the positive electrode material layer, which can further reduce the discharge impedance of the electrochemical device, increase the initial discharge voltage, compensate for the voltage drop caused by the thick coating technology, and thus further improve the discharge capacity of the electrochemical device.

[0009] In some embodiments of this application, the thickness of the positive electrode tab is T2 mm, the width of the positive electrode tab is K2 mm, 0.02 ≤ T2 ≤ 1, and 1 ≤ K2 ≤ 20. By adjusting the values ​​of T2 and K2 within the range of this application, the thickness and width of the tab can be maximized while matching the overall thickness and width of the electrochemical device, thereby minimizing the discharge impedance of the electrochemical device and increasing the initial discharge voltage.

[0010] In some embodiments of this application, the width of the positive electrode sheet is K1 mm, and the length of the portion of the positive electrode tab located within the positive electrode sheet is L2 mm, where 2 ≤ L2 ≤ K1. Preferably, 2 ≤ L2 ≤ K1 / 2. By adjusting the relationship between the width of the positive electrode sheet and the length of the portion of the positive electrode tab located within the positive electrode sheet within the scope of this application, the length of the portion of the positive electrode tab located within the positive electrode sheet is matched with the width of the positive electrode sheet, which can further reduce the discharge impedance of the electrochemical device, extend the discharge time of the electrochemical device at low temperatures, and enable the electrochemical device to have better discharge performance at low temperatures.

[0011] In some embodiments of this application, the length of the portion of the positive electrode tab extending beyond the positive electrode sheet is L3 mm, where 2 ≤ L3 ≤ 20 mm. By adjusting the value of L3 within the range of this application, the discharge impedance of the electrochemical device can be further reduced, the discharge time of the electrochemical device at low temperatures can be extended, and the electrochemical device can have better discharge performance at low temperatures.

[0012] In some embodiments of this application, the first cathode material satisfies at least one of the following characteristics: 1) the Dv50 of the first cathode material is 0.5 μm to 8 μm; 2) the specific surface area of ​​the first cathode material is 2 m². 2 / g to 40m 2 / g; 3) The specific capacity of the first cathode material is from 140 mAh / g to 190 mAh / g. By adjusting the value of at least one of the Dv50, specific surface area, or specific capacity of the first cathode material within the scope of this application, the electrochemical device can achieve a higher discharge capacity at the required low SOC, thereby the electrochemical device provided by this application has a longer discharge time and a higher discharge capacity at low temperatures.

[0013] In some embodiments of this application, the positive electrode material layer further includes a second positive electrode material, a conductive agent, and a binder. Based on the mass of the positive electrode material layer, the mass percentage of the first positive electrode material is 1% to 20%, the mass percentage of the second positive electrode material is 70% to 89%, the mass percentage of the conductive agent is 1% to 5%, and the mass percentage of the binder is 1% to 5%. By adjusting the mass percentages of the first positive electrode material, the second positive electrode material, the conductive agent, and the binder in the positive electrode material layer within the scope of this application, the electrochemical device can achieve good discharge performance at low temperatures while maintaining high energy density.

[0014] In some embodiments of this application, the second cathode material includes at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide, lithium manganese oxide, or lithium titanate; the conductive agent includes at least one of conductive carbon black, carbon nanotubes, or graphene; and the binder includes at least one of polyvinylidene fluoride or lithium polyacrylate. By controlling the type of the second cathode material within the scope of this application, the electrochemical device can achieve good discharge performance at low temperatures while maintaining high energy density.

[0015] A second aspect of this application provides an electrochemical device comprising the electrode assembly of any of the foregoing embodiments. Therefore, the electrochemical device provided by this application can maintain good discharge performance under low-temperature conditions.

[0016] A third aspect of this application provides an electrical device that includes the electrochemical device in any of the foregoing embodiments. Therefore, the electrical device provided by this application has excellent performance.

[0017] The beneficial effects of this application are:

[0018] This application provides an electrode assembly, an electrochemical device, and an electrical device. The electrode assembly includes at least one positive electrode, which comprises a positive current collector and a positive electrode material layer disposed on two surfaces of the current collector. The positive electrode material layer includes a first positive electrode material, LiMn. x Fe 1-x The electrode assembly uses PO4, where 0 ≤ x < 0.95, and has a single-sided thickness of T1 μm for the positive electrode material layer, where 22 ≤ T1 ≤ 110. The length of the positive electrode sheet is L1 mm. The electrode assembly also includes at least one positive electrode tab. When there is only one positive electrode tab, it is a centrally located tab structure; or, when there are multiple positive electrode tabs, the ratio of the number of positive electrode tabs to L1 is B, where 0.002 ≤ B ≤ 0.01. This electrode assembly, by synergistically controlling the type of positive electrode material, the single-sided thickness of the positive electrode material layer, and the structure of the positive electrode tab, enables the electrochemical device to exhibit good discharge performance at low temperatures, thereby improving the user experience during the use of the electrochemical device.

[0019] 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

[0020] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other embodiments can be obtained based on these drawings.

[0021] Figure 1 is a low-temperature discharge curve of Embodiment 1-1 and Comparative Example 1 of this application;

[0022] Figure 2 is a schematic diagram of the structure of the positive electrode sheet in one embodiment of this application;

[0023] Figure 3 is a schematic diagram of the structure of the electrode assembly in some embodiments of this application. Detailed Implementation

[0024] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only 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.

[0025] It should be noted that, in the following explanation, lithium-ion batteries are used as an example of electrochemical devices to illustrate this application; however, the electrochemical devices of this application are not limited to lithium-ion batteries. The specific technical solution is as follows:

[0026] A first aspect of this application provides an electrode assembly comprising at least one positive electrode sheet, the positive electrode sheet comprising a positive current collector and a positive electrode material layer disposed on two surfaces of the positive current collector, wherein the positive electrode material layer comprises a first positive electrode material LiMn. x Fe 1-x PO4, 0≤x<0.95, the single-sided thickness of the positive electrode material layer is T1μm, 22≤T1≤110; for example, T1 can be 22, 23, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110 or a range of any two of the above values.

[0027] In some embodiments of this application, the electrode assembly further includes at least one positive electrode tab. When the number of positive electrode tabs N is one, the positive electrode tab has a centrally located structure. The aforementioned centrally located structure means that the positive electrode tab is positioned in the exact center of the positive electrode sheet, with one part of the positive electrode tab inside the positive electrode sheet and the other part extending beyond it. When the number of positive electrode tabs N is one, this application does not impose any particular limitation on the size of the positive electrode sheet, as long as the purpose of this application can be achieved. For example, as shown in Figure 2, for ease of understanding, a two-dimensional rectangular coordinate system is established with the length direction of the positive electrode sheet 10 itself as the X direction and the width direction of the positive electrode sheet 10 itself as the Y direction. Along the X direction, the length L1 of the positive electrode sheet 10 can be from 100mm to 2500mm, and along the Y direction, the width K1 of the positive electrode sheet 10 can be from 20mm to 200mm.

[0028] In some other embodiments of this application, the length of the positive electrode is L1 mm. When the number of positive electrode tabs N is multiple, the ratio of the number of positive electrode tabs N to L1 is B, where 0.002 ≤ B ≤ 0.01. For example, B can be 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.01, or a range of any two of the above values. When the number of positive electrode tabs N is multiple, this application does not impose any particular limitation on the size of the positive electrode, as long as the purpose of this application is achieved. For example, the length L1 of the positive electrode can be from 100 mm to 2500 mm, and the width K1 of the positive electrode can be from 20 mm to 200 mm. When there are multiple positive electrode tabs N, if the ratio B of the number of positive electrode tabs N to L1 is too small (e.g., less than 0.002), the discharge impedance of the electrochemical device cannot be effectively reduced, resulting in a low initial discharge voltage, which leads to a low discharge capacity and a shortened discharge time. Alternatively, if the ratio B is too large (e.g., greater than 0.01), the discharge impedance of the corresponding electrochemical device is small and the heat generation is low, which cannot increase the downstream discharge voltage in time, resulting in a low discharge capacity and a shortened discharge time.

[0029] The inventors discovered that, on the one hand, LiMn x Fe 1-x The PO4 discharge curve has a flat and moderate low voltage plateau, and LiMn x Fe 1-x The PO4 platform voltage is 3.3V to 3.6V, and it has a high discharge capacity at the required low SOC. Additionally, electrochemical devices typically have power consumption requirements at startup, a temperature range of 0°C to 25°C, and a rate capability range of 0°C to 1°C. LiMn... x Fe 1-x PO4 can also meet the start-up discharge rate requirements of electrochemical devices. On the other hand, the combination of centrally located tabs and multi-tab structures with thick coating technology on the positive electrode can reduce discharge impedance, increase the initial discharge voltage, compensate for the voltage drop introduced by the thick coating technology, and improve the discharge capacity and extend the discharge time of the electrochemical device under low-temperature conditions. Furthermore, in low-temperature environments, the thick coating technology can increase the internal temperature rise of the electrochemical device during discharge, thereby further improving the discharge capacity and extending the discharge time under low-temperature conditions. Simultaneously, the thick coating technology can compensate for the voltage drop introduced by LiMn. x Fe 1-x The low specific capacity of PO4 leads to energy density loss. Furthermore, LiMn... x Fe 1-x PO4 is a low-cost material, which can also reduce application costs. When the thickness of the cathode material layer on one side is too small, for example, less than 22 μm, it cannot effectively increase the internal temperature rise of the electrochemical device during discharge; when the thickness of the cathode material layer on one side is too large, for example, greater than 110 μm, the discharge impedance is too high, leading to rapid discharge cutoff and shortened discharge time. Therefore, by synergistically controlling the type of cathode material, the thickness of the cathode material layer on one side, and the structure of the cathode tab, the advantages of these three factors can be complemented, extending the discharge time of the electrochemical device at low temperature and low voltage. This enables the electrochemical device to have good discharge performance at low temperatures, thereby improving the user experience when using the electrochemical device. In this application, low voltage refers to a voltage less than or equal to 3.7V, and low SOC refers to an SOC less than or equal to 30%.

[0030] Based on the above research findings, the positive electrode material layer of the electrode assembly provided in this application includes a first positive electrode material LiMn. x Fe 1-x PO4, the single-sided thickness of the positive electrode material layer is T1μm, 22≤T1≤110, and the positive electrode sheet in the electrode assembly of this application has the above structure. By synergistically controlling the type of positive electrode material, the single-sided thickness of the positive electrode material layer and the structure of the positive electrode tab, the electrochemical device can have good discharge performance at low temperature, thereby improving the user experience in using the electrochemical device product.

[0031] In some embodiments of this application, when the number of positive electrode tabs N is multiple, the ratio of the number of positive electrode tabs N to T1 is A, where 0.05 ≤ A ≤ 0.1. For example, A can be 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, or a range of any two of the above values. By adjusting the value of A within the range of this application, the number of positive electrode tabs is matched with the single-sided thickness of the positive electrode material layer, which can further reduce the discharge impedance of the electrochemical device, increase the initial discharge voltage, compensate for the voltage drop caused by the thick coating technology, and thus further improve the discharge capacity of the electrochemical device.

[0032] In some embodiments of this application, the thickness of the positive electrode tab is T2mm, as shown in Figure 2, and the width of the positive electrode tab 11 is K2mm, where 0.02≤T2≤1 and 1≤K2≤20. Exemplarily, T2 can be 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, or a range consisting of any two of the above values, and K2 can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, or a range consisting of any two of the above values. By adjusting the values ​​of T2 and K2 within the scope of this application, it is possible to maximize the thickness and width of the tabs while matching the overall thickness and width of the electrochemical device, thereby minimizing the discharge impedance of the electrochemical device and increasing the initial discharge voltage.

[0033] In some embodiments of this application, as shown in Figure 2, the width of the positive electrode 10 is K1 mm, and the length of the portion of the positive electrode tab 11 located within the positive electrode 10 is L2 mm, where 2 ≤ L2 ≤ K1. Preferably, 2 ≤ L2 ≤ K1 / 2. By adjusting the relationship between the width of the positive electrode and the length of the portion of the positive electrode tab located within the positive electrode within the scope of this application, the length of the portion of the positive electrode tab located within the positive electrode is matched with the width of the positive electrode, which can further reduce the discharge impedance of the electrochemical device, extend the discharge time of the electrochemical device at low temperatures, and enable the electrochemical device to have better discharge performance at low temperatures.

[0034] In some embodiments of this application, as shown in Figure 2, the length of the portion of the positive electrode tab 11 extending beyond the positive electrode plate 10 is L3 mm, where 2 ≤ L3 ≤ 20. Exemplarily, L3 can be 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, or a range consisting of any two of the above values. By adjusting the value of L3 within the range specified in this application, the discharge impedance of the electrochemical device can be further reduced, the discharge time of the electrochemical device at low temperatures can be extended, and the electrochemical device can exhibit better discharge performance at low temperatures.

[0035] In some embodiments of this application, the Dv50 of the first cathode material is from 0.5 μm to 8 μm. Exemplarily, the Dv50 of the first cathode material can be 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, or a range consisting of any two of the above values. In some embodiments of this application, the specific surface area of ​​the first cathode material is 2 m². 2 / g to 40m 2 / g. For example, the specific surface area of ​​the first cathode material can be 2m². 2 / g、5m 2 / g, 10m 2 / g, 15m 2 / g、20m 2 / g、25m 2 / g、30m 2 / g、35m 2 / g、40m 2 / g or a range of any two of the above values. In some embodiments of this application, the specific capacity of the first cathode material is from 140 mAh / g to 190 mAh / g. Exemplarily, the specific capacity of the first cathode material can be 140 mAh / g, 145 mAh / g, 150 mAh / g, 155 mAh / g, 160 mAh / g, 165 mAh / g, 170 mAh / g, 175 mAh / g, 180 mAh / g, 185 mAh / g, 190 mAh / g or a range of any two of the above values. By adjusting the value of at least one of the Dv50, specific surface area, or specific capacity of the first cathode material within the range of this application, the electrochemical device can achieve a higher discharge capacity at the required low SOC, thereby providing the electrochemical device with a longer discharge time and higher discharge capacity at low temperatures.

[0036] In this application, Dv50 refers to the particle size that reaches 50% of the volumetric accumulation in the particle size distribution of the material based on volume.

[0037] This application does not impose any particular restrictions on the methods for controlling the Dv50, specific surface area, and specific capacity of the first cathode material, as long as the purpose of this application is achieved. For example, extending the mechanical mixing time decreases Dv50 and increases the specific surface area; shortening the mechanical mixing time increases Dv50 and decreases the specific surface area. Generally, even with the same type of first cathode material, the Dv50 and specific surface area of ​​the first cathode material also affect its specific capacity. In this application, decreasing the Dv50 of the first cathode material increases the specific surface area and thus increases the specific capacity; conversely, increasing the Dv50 of the first cathode material decreases the specific surface area and thus decreases the specific capacity.

[0038] In some embodiments of this application, the positive electrode material layer further includes a second positive electrode material, a conductive agent, and a binder. Based on the mass of the positive electrode material layer, the mass percentage W1 of the first positive electrode material is 1% to 20%, the mass percentage W2 of the second positive electrode material is 70% to 89%, the mass percentage W3 of the conductive agent is 1% to 5%, and the mass percentage W4 of the binder is 1% to 5%. Exemplarily, the mass percentage W1 of the first positive electrode material can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, or a range of any two of the above values; the mass percentage W2 of the second positive electrode material can be 70%, 71%, 72%, 73%, 74%, 75%, 76%, 79 ... The mass percentages of the conductive agent (W3) can be 7%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, or any combination of two of the above values. Similarly, the mass percentage of the binder (W4) can be 1%, 2%, 3%, 4%, 5%, or any combination of two of the above values. By adjusting the mass percentages of the first positive electrode material, the second positive electrode material, the conductive agent, and the binder in the positive electrode material layer within the scope of this application, the electrochemical device can achieve good discharge performance at low temperatures while maintaining a high energy density.

[0039] In some embodiments of this application, the second cathode material includes at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide, lithium manganese oxide, or lithium titanate; the conductive agent includes at least one of conductive carbon black, carbon nanotubes, or graphene; and the binder includes at least one of polyvinylidene fluoride or lithium polyacrylate. The aforementioned lithium nickel cobalt manganese oxide may include, but is not limited to, LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi0.6 Co 0.2 Mn 0.2 O2(NCM622), LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM523) or LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 At least one of O2 (NCM111). By controlling the type of the second cathode material within the scope of this application, it is possible to enable the electrochemical device to have good discharge performance at low temperatures while also having high energy density.

[0040] This application does not impose any particular restrictions on the material of the positive electrode tab, as long as it can achieve the purpose of this application. For example, it can be at least one of pure aluminum or copper alloy plated with nickel.

[0041] 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).

[0042] This application does not impose any particular limitation on the thickness of the positive electrode current collector, as long as it can achieve the purpose of this application. For example, the thickness of the positive electrode current collector can be 6 μm to 20 μm.

[0043] Optionally, the positive electrode may further include a conductive layer located between the positive current collector and the positive electrode material layer. This application does not impose any particular limitation on the composition of the conductive layer, which can be a conductive layer commonly used in the art. The conductive layer includes a conductive agent and a binder. This application does not impose any particular limitation on the conductive agent and binder in the conductive layer; for example, it can be at least one of the aforementioned conductive agents and binders.

[0044] In this application, the electrode assembly further includes a negative electrode sheet, which 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 "surface" here can be the entire surface area of ​​the negative electrode current collector, or only a portion of the surface area; this application does not have any particular limitation, as long as the purpose of this application is achieved.

[0045] 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 collectors (such as carbon copper composite current collectors, nickel copper composite current collectors, titanium copper composite current collectors, etc.).

[0046] This application does not impose any particular restrictions on the material of the negative electrode tab, as long as it can achieve the purpose of this application. For example, it can be at least one of pure nickel, aluminum-nickel composite strip, copper-plated nickel, copper alloy-plated nickel, pure copper adapter copper-plated nickel, or copper alloy-plated nickel.

[0047] In this application, the negative electrode material layer includes a negative electrode active material. The negative electrode active material of this application may include natural graphite, artificial graphite, mesophase microcarbon spheres (MCMB), hard carbon, soft carbon, silicon-based active materials, Li-Sn alloys, Li-Sn-O alloys, Sn, SnO, SnO2, and spinel-structured lithium titanate Li4Ti5O. 12 The anode active material can be one or more of Li-Al alloys and metallic lithium. For example, the anode active material may include artificial graphite and silicon-based active material, with a mass ratio of artificial graphite to silicon-based active material of (100 to 0):(0 to 100); the silicon-based active material may include one or more of SiC, SiO, or elemental Si, with a mass ratio of SiC, SiO, and elemental Si of (1 to 0):(0 to 1):(0 to 1). This application does not impose any particular limitation on the particle size distribution Dv10, Dv50, and Dv90 of the anode active material, as long as the purpose of this application can be achieved. For example, the Dv10 of the anode active material can be 2 μm to 11 μm, the Dv50 can be 12 μm to 20 μm, and the Dv90 can be 21 μm to 28 μm. This application does not impose any particular limitation on the specific surface area of ​​the anode active material, as long as the purpose of this application can be achieved. For example, the specific surface area of ​​the anode active material can be 0.5 m². 2 / g to 3m 2 / g. This application does not impose any particular limitation on the specific capacity of the negative electrode active material, as long as it can achieve the purpose of this application. For example, the specific capacity of the negative electrode active material can be from 400mAh / g to 1000mAh / g.

[0048] In this application, Dv10 refers to the particle size that reaches 10% of the volumetric cumulative size in the particle size distribution of the material based on the volumetric reference, and Dv90 refers to the particle size that reaches 90% of the volumetric cumulative size in the particle size distribution of the material based on the volumetric reference.

[0049] The negative electrode material layer also includes a conductive agent and / or a binder. This application does not impose any particular restrictions on the types of conductive agents and binders, as long as they achieve the purpose of this application. For example, it can be at least one of the aforementioned conductive agents and binders. This application does not impose any particular restrictions on the mass ratio of the negative electrode active material, conductive agent, and 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.

[0050] This application does not impose any particular limitation on the thickness of the negative electrode material layer, as long as it achieves the purpose of this application. For example, the thickness of the negative electrode material layer can be from 30 μm to 150 μm. This application does not impose any particular limitation on the thickness of the negative electrode current collector, as long as it achieves the purpose of this application. For example, the thickness of the negative electrode current collector can be from 3 μm to 16 μm. This application does not impose any particular limitation on the thickness of the negative electrode sheet, as long as it achieves the purpose of this application. For example, the thickness of the negative electrode sheet can be from 50 μm to 250 μm.

[0051] Optionally, the negative electrode may further include a conductive layer 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 conductive layer, which can be a conductive layer commonly used in the art. The conductive layer includes a conductive agent and a binder. This application does not impose any particular limitation on the conductive agent and binder in the conductive layer; for example, it can be at least one of the aforementioned conductive agents and binders.

[0052] In this application, the electrode assembly also includes a separator membrane to separate the positive and negative electrode plates, prevent short circuits within the electrochemical device, allow electrolyte ions to pass freely, and not affect the electrochemical charging and discharging process. This application does not impose any particular limitation on the separator membrane, as long as it achieves the purpose of this application. For example, the material of the separator membrane 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 type of separator membrane may include at least one of woven membrane, nonwoven membrane, microporous membrane, composite membrane, rolled membrane, or spun membrane. For example, the separator membrane may include a substrate layer and a surface treatment layer. The substrate layer may be a nonwoven fabric, membrane, 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 can be used. Optionally, a surface treatment layer is provided on at least one surface of the substrate layer. The surface treatment layer can be a polymer layer or an inorganic layer, or a layer formed by mixing polymers and inorganic materials. For example, the inorganic layer includes inorganic particles and a binder. The inorganic particles are not particularly limited and may include at least one of 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. The binder is not particularly limited and may be at least one of the binders mentioned above. The polymer layer contains a polymer, and the polymer material includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, or polyvinylidene fluoride or poly(vinylidene fluoride-hexafluoropropylene).

[0053] A second aspect of this application provides an electrochemical device comprising the electrode assembly of any of the foregoing embodiments. Therefore, the electrochemical device provided by this application can maintain good discharge performance under low-temperature conditions.

[0054] The electrochemical device of this application further includes an electrolyte, which comprises a lithium salt and a non-aqueous solvent. The lithium salt may include various lithium salts commonly used in the art, such as at least one of lithium hexafluorophosphate (LiPF6), LiBF4, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalato)borate (LiBOB), or lithium difluoroborate. This application does not impose any particular limitation on the mass percentage of the lithium salt in the electrolyte, as long as the purpose of this application is achieved. This application also does not impose any particular limitation on the non-aqueous solvent, as long as the purpose of this application is achieved, such as including but not limited to at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, or other organic solvents. 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). The aforementioned fluorinated carbonate 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, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate. In this application, the electrolyte may also include additives, which may be one or more of fluoroethylene carbonate, benzene derivatives, 1,3-propanesulfonate lactone, ethyl propionate, adiponitrile, or glutaronitrile.The aforementioned benzene derivatives may be one or more of biphenyl, cyclohexylbenzene, tert-amylbenzene, terphenyl, and dibenzofuran, wherein the mass ratio of biphenyl, cyclohexylbenzene, tert-amylbenzene, terphenyl, and dibenzofuran may be (1 to 0):(0 to 1):(0 to 1):(0 to 1):(0 to 1):(0 to 1).

[0055] The electrochemical device of this application also includes a packaging bag for containing the electrode assembly and electrolyte, as well as other components known in the art in the electrochemical device. This application does not limit the scope of these other components. This application does not impose any particular limitation on the packaging bag; it can be any packaging bag known in the art, as long as it achieves the purpose of this application.

[0056] The electrochemical device described in this application is not particularly limited and may include any device in which an electrochemical reaction occurs. In some embodiments, the electrochemical device 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.

[0057] The preparation process of the electrochemical device described in this application is well known to those skilled in the art, and this application does not impose any particular limitations. For example, it 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 in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain the electrochemical device; or 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 in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain the electrochemical device. In addition, overcurrent protection elements, conductive plates, etc., may be placed in the packaging bag as needed to prevent pressure rise and overcharging / discharging inside the electrochemical device. The packaging bag is any packaging bag known in the art, and this application does not limit its use.

[0058] A third aspect of this application provides an electrical device that includes the electrochemical device in any of the foregoing embodiments. Therefore, the electrical device provided by this application has excellent performance.

[0059] This application does not specifically limit the type of electrical device; it can be any electrical device known in the prior art. In some embodiments, the electrical 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.

[0060] Example

[0061] 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.

[0062] Test methods and equipment:

[0063] Particle size testing:

[0064] The particle size of the sample was measured using a laser particle size analyzer (MasterSizer 2000). 0.02 g of sample was added to a 50 mL clean beaker, followed by 20 mL of ethanol dispersant to completely disperse the sample. After ultrasonication for 30 min in a 120 W ultrasonic cleaner, the sample was added to the laser particle size analyzer to measure its Dv10, Dv50, and Dv90.

[0065] Specific surface area test:

[0066] According to the national standard "Determination of Specific Surface Area of ​​Solid Substances by Gas Adsorption BET Method" (GB / T 19587-2017), the specific surface area of ​​the sample was tested by nitrogen adsorption using a specific surface area analyzer (model TristarⅡ3020M).

[0067] Gram capacity test:

[0068] In a drying room at 25°C and RH ≤2%, the active material, binder polyvinylidene fluoride, and conductive agent acetylene black were mixed in a mass ratio of 80:10:10. An appropriate amount of N-methylpyrrolidone (NMP) solvent was added, and the mixture was thoroughly stirred to form a uniform positive electrode slurry (75 wt% solid content). This positive electrode slurry was coated onto a 10 μm thick aluminum foil (positive electrode current collector), then dried and cold-pressed. It was then punched into small round pieces with a diameter of 14 mm to be used as the positive electrode sheet. A 14 mm diameter lithium sheet was used as the negative electrode sheet, and a 16 mm diameter, 12 μm thick polyethylene film was used as the separator. A coin cell half-cell was assembled using the electrolyte from Example 1.

[0069] The half-cell was charged and discharged using the LAND CT2001A battery testing system. The operating voltage range was 0.01V to 2V, and the current density was 10mA / g. The initial discharge capacity was recorded.

[0070] When the above-mentioned active material is the first positive electrode material, the measured first discharge specific capacity is the discharge specific capacity of the first positive electrode material; when the above-mentioned active material is the negative electrode active material (composed of artificial graphite and SiO in a mass ratio of 50:50), the measured first discharge specific capacity is the discharge specific capacity of the negative electrode active material.

[0071] Low-temperature discharge test:

[0072] The lithium-ion battery was left to stand at 25°C for 5 minutes, then discharged at a constant current of 0.5C to 3.0V, left to stand for another 5 minutes, charged at a constant current of 0.1C for 2 hours, left to stand for 5 minutes, and then left to stand in a high and low temperature chamber at 0°C for 2 hours. After that, it was discharged at a constant current of 1C to 3.0V, and the discharge time was recorded as t min.

[0073] Measurements of the length L1 and width K1 of the positive electrode plate, the thickness T2 and width K2 of the positive electrode tab, the length L2 of the portion of the positive electrode tab inside the positive electrode plate, and the length L3 of the portion of the positive electrode tab extending beyond the positive electrode plate:

[0074] The length and width of the positive electrode plate, the width of the positive electrode tab, the length of the portion of the positive electrode tab inside the positive electrode plate, and the length of the portion of the positive electrode tab extending beyond the positive electrode plate were measured using a ruler. The measurements were taken three times and the average value was taken.

[0075] The thickness of the positive electrode tab was measured using a micrometer, and the average value was taken after three measurements.

[0076] Example 1-1

[0077] <Preparation of the positive electrode>

[0078] In a stirred tank, the first positive electrode material LiFePO4, the second positive electrode material lithium cobalt oxide, the conductive agent conductive carbon black, and the binder polyvinylidene fluoride were mixed in a mass ratio of 5:89:3:3. N-methylpyrrolidone (NMP) solvent was added, and the mixture was thoroughly stirred to form a positive electrode slurry with a solid content of 75 wt%. The positive electrode slurry was uniformly coated onto one surface of a 10 μm thick aluminum foil and dried at 85°C to obtain a single-sided positive electrode sheet with a coating thickness of 100 μm. The above steps were then repeated on the other surface of the aluminum foil to obtain a double-sided positive electrode sheet. After cold pressing, slitting, and welding a positive electrode tab, the sheet was vacuum dried at 85°C for 4 hours to obtain a positive electrode sheet with dimensions of 74 mm × 867 mm for later use. The positive electrode tab is a centrally located structure and is made of pure aluminum. The first cathode material has a Dv50 of 4.5 μm and a specific surface area of ​​18.0 m². 2 / g, the specific capacity of the first cathode material is 165mAh / g.

[0079] <Preparation of Negative Electrode Sheets>

[0080] In a stirred tank, the negative electrode active material, conductive carbon black, styrene-butadiene rubber, and sodium carboxymethyl cellulose were mixed in a mass ratio of 96:2:1:1. Deionized water was added as a solvent, and the mixture was stirred until homogeneous, yielding a negative electrode slurry with a solid content of 40 wt%. The negative electrode slurry was uniformly coated onto one surface of a 6 μm thick copper foil used as a negative electrode current collector, and dried at 85°C to obtain a single-sided coated negative electrode sheet with a 100 μm coating thickness. The above steps were then repeated on the other surface of the copper foil to obtain a double-sided coated negative electrode sheet. After cold pressing, cutting, and welding a negative electrode tab, the sheet was vacuum dried at 85°C for 12 hours to obtain a negative electrode sheet with dimensions of 78 mm × 875 mm for later use. The negative electrode tab is a centrally located structure made of pure nickel. The negative electrode active material consists of artificial graphite and SiO in a mass ratio of 50:50. The negative electrode active material has a Dv10 of 4 μm, a Dv50 of 16 μm, a Dv90 of 26 μm, a maximum particle size Dmax of 35 μm, and a specific surface area of ​​1.5 m². 2 / g, the specific capacity of the negative electrode active material is 600mAh / g.

[0081] <Preparation of Electrolyte>

[0082] In an argon-filled reactor, ethylene carbonate, diethyl carbonate, propylene carbonate, and propyl propionate are gradually added and mixed thoroughly in a mass ratio of 20:30:30:20 to form a base solvent. Lithium hexafluorophosphate is then added and stirred until completely dissolved to obtain the electrolyte. The lithium hexafluorophosphate comprises 12.5% ​​by mass, with the remainder being the base solvent.

[0083] <Preparation of the separating membrane>

[0084] The coating layer is uniformly coated on both surfaces of the diaphragm substrate. The thickness of the diaphragm substrate is 9 μm. The material of the diaphragm substrate is polyethylene. The total thickness of the coating layer is 3 μm. The coating layer is a mixture of alumina and polyvinylidene fluoride (mass ratio of 9:1).

[0085] <Preparation of Lithium-ion Batteries>

[0086] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. The electrode assembly is then wound to obtain the electrode assembly. As shown in Figure 3, the electrode assembly 100 includes a positive electrode tab 11 and a negative electrode tab 12. Along the X direction, the electrode assembly 100 includes opposing first edges 101 and second edges 102. The distance between the positive electrode tab edge 110 (closer to the first edge 101) and the first edge 101 is 7 mm, and the distance between the negative electrode tab edge 120 (closer to the second edge 102) and the second edge 102 is 10 mm. The thickness T2 of the positive electrode tab, the width K2 of the positive electrode tab, the length L1 of the positive electrode, the length L2 of the portion of the positive electrode tab inside the positive electrode, and the length L3 of the portion of the positive electrode tab extending beyond the positive electrode are shown in Table 1. The electrode assembly is placed in the outer packaging foil and dehydrated at 80°C. The prepared electrolyte is then injected, and the lithium-ion battery is obtained through vacuum sealing, settling, formation, shaping, and capacity testing.

[0087] Examples 1-2

[0088] Except that in the "Preparation of Positive Electrode Sheet", the positive electrode sheet includes 10 positive electrode tabs, and in the "Preparation of Lithium-ion Battery", each layer of positive electrode sheet in the electrode assembly winding structure includes one positive electrode tab, the relative position of each positive electrode tab in the electrode assembly is the same as in Example 1-1, and the relevant preparation parameters are adjusted according to Table 1, the rest is the same as in Example 1-1.

[0089] Examples 1-3

[0090] Except that in the <Preparation of Positive Electrode Sheet>, the positive electrode sheet includes 10 positive electrode tabs, and in the <Preparation of Lithium-ion Battery>, the electrode assembly is a stacked structure with each layer of positive electrode sheet including one positive electrode tab, the relative position of each positive electrode tab in the electrode assembly is the same as in Example 1-1, and the relevant preparation parameters are adjusted according to Table 1, the rest is the same as in Example 1-1.

[0091] Examples 1-4 to Examples 1-24

[0092] Except for adjusting the relevant preparation parameters according to Table 1 in <Preparation of Positive Electrode> and <Preparation of Lithium-ion Battery>, the rest are the same as in Examples 1-2.

[0093] Examples 2-1 to 2-9

[0094] Except for adjusting the relevant preparation parameters according to Table 2 in the <Preparation of Positive Electrode> section, the rest is the same as in Examples 1-2.

[0095] Comparative Example 1

[0096] Except for the preparation of the positive electrode sheet according to the following steps, the rest is the same as in Example 1-1.

[0097] <Preparation of the positive electrode>

[0098] In a stirred tank, lithium nickel cobalt manganese oxide (NCM523), conductive carbon black (conductive agent), and polyvinylidene fluoride (PVDF) (binder) were mixed at a mass ratio of 95:2.5:2.5. N-methylpyrrolidone (NMP) solvent was added, and the mixture was thoroughly stirred to form a positive electrode slurry with a solid content of 70 wt%. The positive electrode slurry was uniformly coated onto one surface of a 10 μm thick aluminum foil and dried at 85°C to obtain a single-sided coated positive electrode sheet with a coating thickness of 100 μm. The above steps were then repeated on the other surface of the aluminum foil to obtain a double-sided coated positive electrode sheet. After cold pressing, slitting, and welding a positive electrode tab, the sheet was vacuum dried at 85°C for 4 hours to obtain a positive electrode sheet with dimensions of 74 mm × 867 mm for later use. The positive electrode tab is a centrally located structure and is made of pure aluminum.

[0099] Comparative Example 2

[0100] Except for the preparation of the positive electrode sheet according to the following steps, the rest is the same as in Examples 1-2.

[0101] <Preparation of the positive electrode>

[0102] In a stirred tank, lithium nickel cobalt manganese oxide (NCM523), conductive carbon black (conductive agent), and polyvinylidene fluoride (PVDF) (binder) were mixed at a mass ratio of 95:2.5:2.5. N-methylpyrrolidone (NMP) solvent was added, and the mixture was thoroughly stirred to form a positive electrode slurry with a solid content of 65 wt%. The positive electrode slurry was uniformly coated onto one surface of a 10 μm thick aluminum foil and dried at 85°C to obtain a single-sided coated positive electrode sheet with a coating thickness of 100 μm. The above steps were then repeated on the other surface of the aluminum foil to obtain a double-sided coated positive electrode sheet. After cold pressing, slitting, and welding of positive electrode tabs, the sheet was vacuum dried at 85°C for 4 hours to obtain a positive electrode sheet with dimensions of 74 mm × 1000 mm for later use.

[0103] Comparative Examples 3 to 4

[0104] Except for adjusting the relevant preparation parameters according to Table 1 in <Preparation of Positive Electrode> and <Preparation of Lithium-ion Battery>, the rest are the same as in Examples 1-2.

[0105] In the above embodiments 1-2, 1-4 to 1-24 and comparative examples 2 to 4, when the electrode assembly is a wound structure, each layer of positive electrode sheet is provided with a positive electrode tab, and the positive electrode tabs are in the same relative position in the electrode assembly. That is, the distance between the positive electrode tab edge 110 near the first edge 101 and the first edge 101 is 7 mm, and the distance between the negative electrode tab edge 120 near the second edge 102 and the second edge 102 is 10 mm. The width of the electrode assembly (i.e. the width in the X direction in Figure 3) varies with the width of the positive electrode sheet.

[0106] In the above embodiments and comparative examples, when the length L1 and width K1 of the positive electrode sheet change, the length and width of the negative electrode sheet change accordingly, and the difference between the length of the positive electrode sheet and the length of the negative electrode sheet is the same as in Embodiment 1-1, and the difference between the width of the positive electrode sheet and the width of the negative electrode sheet is the same as in Embodiment 1-1.

[0107] The preparation parameters and electrical performance parameters of each embodiment and comparative example are shown in Table 1 and Table 2.

[0108] Table 1

[0109] Note: In Table 1, " / " indicates that there are no relevant preparation parameters.

[0110] As can be seen from Examples 1-1 to 1-24 and Comparative Examples 1 to 4, when the type of positive electrode material, the single-sided thickness T1 of the positive electrode material layer, the ratio B of the number of positive electrode tabs to the length L1 of the positive electrode sheet, and the structure of the positive electrode tabs are within the scope of this application, the lithium-ion battery has a longer low-temperature discharge time, which shows that the lithium-ion battery has better discharge performance at low temperatures, thereby improving the user experience when using lithium-ion battery products.

[0111] Specifically, Figure 1 shows the low-temperature discharge curves of the lithium-ion batteries in Example 1-1 and Comparative Example 1. It can be seen from the figure that the lithium-ion battery in Example 1-1 has a longer low-temperature discharge time, indicating that the lithium-ion battery in Example 1-1 has better discharge performance at low temperatures.

[0112] The ratio A of the number of positive electrode tabs N to the single-sided thickness T1 of the positive electrode material layer typically affects the low-temperature discharge performance of lithium-ion batteries. As can be seen from Examples 1-6, 1-7, 1-23, and 1-24, when the value of A is within the range of this application, the lithium-ion battery exhibits a longer low-temperature discharge time, thus demonstrating that the lithium-ion battery has better discharge performance at low temperatures.

[0113] The thickness T2 and width K2 of the positive electrode tab typically affect the low-temperature discharge performance of lithium-ion batteries. As can be seen from Examples 1-1 to 1-24, when the values ​​of T2 and K2 are within the range of this application, the lithium-ion batteries exhibit a longer low-temperature discharge time, thus demonstrating that lithium-ion batteries have good discharge performance at low temperatures.

[0114] The relationship between the width K1 of the positive electrode and the length L2 of the portion of the positive electrode tab located within the positive electrode typically affects the low-temperature discharge performance of lithium-ion batteries. As can be seen from Examples 1-1 to 1-24, within the scope of this application, the lithium-ion battery exhibits a longer low-temperature discharge time due to the relationship between K1 and L2, thus demonstrating good discharge performance at low temperatures.

[0115] The length L3 of the portion of the positive electrode tab extending beyond the positive electrode sheet typically affects the low-temperature discharge performance of lithium-ion batteries. As can be seen from Examples 1-1 to 1-24, when the value of L3 is within the range specified in this application, the lithium-ion battery exhibits a longer low-temperature discharge time, thus demonstrating good discharge performance at low temperatures.

[0116] Table 2

[0117] As can be seen from Examples 2-1 to 2-5, when the type of positive electrode material, the single-sided thickness of the positive electrode material layer, and the structure of the positive electrode tab are within the scope of this application, the lithium-ion battery has a longer low-temperature discharge time, which indicates that the lithium-ion battery has better discharge performance at low temperatures, thereby improving the user experience when using lithium-ion battery products.

[0118] The mass percentages W1 (first cathode material), W2 (second cathode material), W3 (conductive agent), and W4 (binder) typically affect the energy density of a lithium-ion battery. As can be seen from Examples 2-6 to 2-9, when the values ​​of W1, W2, W3, and W4 are within the range specified in this application, the lithium-ion battery exhibits a longer low-temperature discharge time, thus demonstrating that the lithium-ion battery has better discharge performance at low temperatures.

[0119] The above description is merely a preferred embodiment of this application and is not intended to limit the scope of protection of this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application are included within the scope of protection of this application.

Claims

1. An electrode assembly comprising at least one positive electrode sheet, the positive electrode sheet comprising a positive current collector and a layer of positive electrode material disposed on both surfaces of the positive current collector, wherein, The positive electrode material layer includes a first positive electrode material LiMn x Fe 1-x PO4, 0≤x<0.95, A single-face thickness of the positive electrode material layer is T1 μm, 22 ≤ T1 ≤ 110; A length of the positive electrode tab is L1 mm; The electrode assembly further comprises at least one positive electrode tab, When the number of the positive electrode tabs is one, the positive electrode tab is a middle tab structure; or, When the number of the positive electrode tabs is multiple, a ratio of the number of the positive electrode tabs to the L1 is B, 0.002 ≤ B ≤ 0.

01.

2. The electrode assembly of claim 1, wherein, When the number of the positive electrode tabs is multiple, a ratio of the number of the positive electrode tabs to the T1 is A, 0.05 ≤ A ≤ 0.

1.

3. The electrode assembly of claim 1, wherein, A thickness of the positive electrode tab is T2 mm, a width of the positive electrode tab is K2 mm, 0.02 ≤ T2 ≤ 1, and 1 ≤ K2 ≤ 20.

4. The electrode assembly of claim 1, wherein, A width of the positive electrode tab is K1 mm, a length of a part of the positive electrode tab located in the positive electrode tab is L2 mm, 2 ≤ L2 ≤ K1.

5. The electrode assembly of claim 4, wherein, A length of a part of the positive electrode tab exceeding the positive electrode tab is L3 mm, 2 ≤ L3 ≤ 20.

6. The electrode assembly of claim 1, wherein, The first positive electrode material satisfies at least one of the following characteristics: 1) a Dv50 of the first positive electrode material is 0.5 μm to 8 μm; 2) the specific surface area of the first positive electrode material is 2 m 2 / g to 40 m 2 / g; 3) a gravimetric capacity of the first positive electrode material is 140 mAh / g to 190 mAh / g.

7. The electrode assembly of claim 1, wherein, The positive electrode material layer further comprises a second positive electrode material, a conductive agent, and a binder, a mass percentage content of the first positive electrode material is 1% to 20%, a mass percentage content of the second positive electrode material is 70% to 89%, a mass percentage content of the conductive agent is 1% to 5%, and a mass percentage content of the binder is 1% to 5%, based on a mass of the positive electrode material layer.

8. The electrode assembly of claim 7, wherein, The second positive electrode material comprises at least one of nickel cobalt manganese acid lithium, nickel cobalt aluminum acid lithium, iron lithium phosphate, lithium-rich manganese-based material, cobalt acid lithium, manganese acid lithium, or titanium acid lithium, the conductive agent comprises at least one of conductive carbon black, carbon nanotube, or graphene, and the binder comprises at least one of polyvinylidene fluoride or lithium polyacrylate.

9. An electrochemical device comprising the electrode assembly of any one of claims 1 to 8.

10. An electric device comprising the electrochemical device of claim 9.

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