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

Electrode assembly, electrochemical device, and electrical device

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on June 29, 2023, with application number 202310788604.6 and invention name “An electrode assembly, electrochemical device and electrical device”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of electrochemical technology, and in particular to an electrode assembly, an electrochemical device, and an electrical device. Background Art

[0003] Lithium-ion batteries offer numerous advantages, including high specific energy density, long cycle life, high nominal voltage, low self-discharge, compact size, and light weight. They are widely used in portable electronic devices, electric bicycles, electric vehicles, and energy storage devices. Technologists are constantly improving the performance of lithium-ion batteries, and they will continue to play a key role in the consumer electronics sector for a long time.

[0004] During the use of lithium-ion batteries, temperature is a significant factor affecting their discharge performance. As the temperature decreases, the discharge voltage and SOC (State of Charge) of a lithium-ion battery decrease. Some existing products using lithium-ion batteries experience issues with full startup and rapid discharge in low-temperature environments (e.g., temperatures less than or equal to 10°C). Therefore, there is a need for lithium-ion batteries that can maintain good discharge performance in low-temperature conditions to enhance 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 can have good discharge performance under low temperature conditions. The specific technical solution is as follows:

[0007] The first aspect of the present application provides an electrode assembly comprising at least one positive electrode sheet, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode material layer disposed on both surfaces of the positive electrode current collector, wherein the positive electrode material layer comprises a first positive electrode material LiMn x Fe 1-xPO4, 0≤x<0.95, the thickness of the positive electrode material layer on a single surface is T1μm, 22≤T1≤110; the length of the positive electrode tab is L1mm; the electrode assembly also includes at least one positive electrode tab. When there is one positive electrode tab, the positive electrode tab is a tab-centered structure; alternatively, when there are multiple positive electrode tabs, the ratio of the number of positive electrode tabs to L1 is B, 0.002≤B≤0.01. By synergistically regulating the type of positive electrode material, the thickness of the positive electrode material layer on a single surface, 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 use of the electrochemical device product.

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

[0009] In some embodiments of the present 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 regulating the values ​​of T2 and K2 within the scope of the present application, the thickness and width of the tab can be maximized while matching the thickness and width of the overall electrochemical device, thereby minimizing the discharge impedance of the electrochemical device and increasing the initial discharge voltage.

[0010] In some embodiments of the present 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 regulating 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 the present application, the length of the portion of the positive electrode tab located within the positive electrode sheet matches 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 the present application, the length of the portion of the positive electrode tab extending beyond the positive electrode sheet is L3 mm, where 2 ≤ L3 ≤ 20. By adjusting the value of L3 within the range of the present 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 the present 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 m 2 / g to 40m 2 / g; 3) the gram capacity of the first cathode material is 140 mAh / g to 190 mAh / g. By adjusting at least one of the Dv50, specific surface area, or gram capacity of the first cathode material within the range of this application, the electrochemical device can have a higher discharge capacity at a desired low SOC, thereby providing the electrochemical device with a longer discharge time and higher discharge capacity at low temperatures.

[0013] In some embodiments of the present 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 regulating 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 the present application, the electrochemical device can have good discharge performance under low temperature conditions while having a high energy density.

[0014] In some embodiments of the present application, the second positive electrode material includes at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, a lithium-rich manganese-based material, 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 regulating the type of the second positive electrode material within the scope of the present application, the electrochemical device can have good discharge performance under low temperature conditions while also having a high energy density.

[0015] The second aspect of the present application provides an electrochemical device, which includes the electrode assembly according to any of the aforementioned embodiments. Therefore, the electrochemical device provided by the present application can maintain good discharge performance under low temperature conditions.

[0016] The third aspect of the present application provides an electrical device, which includes the electrochemical device according to any of the aforementioned embodiments. Therefore, the electrical device provided by the present application has good performance.

[0017] Beneficial effects of this application:

[0018] The present application provides an electrode assembly, an electrochemical device, and an electrical device, wherein the electrode assembly includes at least one positive electrode sheet, the positive electrode sheet includes a positive electrode current collector and a positive electrode material layer provided on both surfaces of the positive electrode current collector, the positive electrode material layer includes 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; the length of the positive electrode tab 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 tab-centered 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. The electrode assembly of the present application, by synergistically regulating the type of positive electrode material, the single-sided thickness of the positive electrode material layer, and the structure of the positive electrode tab, can enable the electrochemical device to have good discharge performance at low temperatures, thereby improving the user experience in the process of using the electrochemical device product.

[0019] Of course, it is not necessary to achieve all the advantages described above at the same time when implementing any product or method of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other embodiments can also be obtained based on these drawings.

[0021] FIG1 is a low-temperature discharge curve diagram of Example 1-1 and Comparative Example 1 of the present application;

[0022] FIG2 is a schematic structural diagram of a positive electrode sheet in one embodiment of the present application;

[0023] FIG3 is a schematic structural diagram of an electrode assembly in some embodiments of the present application. DETAILED DESCRIPTION

[0024] The following will be combined with the accompanying drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the embodiments described are only part of the embodiments of the present application, rather than all the 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 description, lithium-ion batteries are used as an example of electrochemical devices to explain this application, but the electrochemical devices of this application are not limited to lithium-ion batteries. The specific technical solution is as follows:

[0026] The first aspect of the present application provides an electrode assembly comprising at least one positive electrode plate, wherein the positive electrode plate comprises a positive electrode current collector and a positive electrode material layer disposed on both surfaces of the positive electrode 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; illustratively, 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 consisting of any two of the above values.

[0027] In some embodiments of the present application, the electrode assembly further includes at least one positive electrode tab. When the number N of positive electrode tabs is one, the positive electrode tab is a tab-centered structure. The above-mentioned tab-centered structure refers to that the positive electrode tab is arranged in the middle of the positive electrode sheet, and a part of the positive electrode tab is located inside the positive electrode sheet, and the other part of the positive electrode tab extends beyond the positive electrode sheet. When the number N of positive electrode tabs is one, the present application does not particularly limit the size of the positive electrode sheet, as long as the purpose of the present 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 100mm to 2500mm, and along the Y direction, the width K1 of the positive electrode sheet 10 can be 20mm to 200mm.

[0028] In other embodiments of the present application, the length of the positive electrode tab is L1mm. When the number of positive electrode tabs N is multiple, the ratio of the number of positive electrode tabs N to L1 is B, 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 consisting of any two of the above values. When the number of positive electrode tabs N is multiple, the present application has no particular restrictions on the size of the positive electrode tab, as long as the purpose of the present application can be achieved. For example, the length L1 of the positive electrode tab can be 100mm to 2500mm, and the width K1 of the positive electrode tab can be 20mm to 200mm. When the number N of positive electrode tabs is multiple, when the ratio B of the number N of positive electrode tabs to L1 is too small (for example, less than 0.002), the discharge impedance of the electrochemical device cannot be effectively reduced, resulting in a low initial discharge voltage, which will lead to a low discharge capacity and a shortened discharge time; or when the ratio B is too large (for example, greater than 0.01), the discharge impedance of the corresponding electrochemical device is small and the heat generation is small, and the rear-end discharge voltage cannot be increased in time, which will lead to a low discharge capacity and a shortened discharge time.

[0029] The inventors have found that, on the one hand, LiMn x Fe 1-x PO4 discharge curve has a flat and moderate low voltage platform, LiMn x Fe 1-x The PO4 platform voltage is 3.3V to 3.6V, and its discharge capacity is high at the required low SOC. In addition, electrochemical devices usually have power consumption requirements for startup, the temperature range is 0℃ to 25℃, the rate range is 0C to 1C, and LiMn x Fe 1-x PO4 can also meet the power-on rate discharge requirements of electrochemical devices. On the other hand, the tab center structure and multi-tab structure are combined with the positive electrode thick coating technology. The tab center structure and multi-tab structure can reduce the discharge impedance, increase the initial discharge voltage, compensate for the voltage drop caused by the thick coating technology, and increase the discharge capacity of the electrochemical device under low temperature conditions and extend its discharge time. Moreover, in a low temperature environment, the thick coating technology can increase the internal temperature rise of the electrochemical device during the discharge process, thereby further increasing the discharge capacity of the electrochemical device under low temperature conditions and extending its discharge time. At the same time, the thick coating technology can compensate for the LiMn x Fe 1-x The problem of energy density loss caused by low gram capacity of PO4. In addition, LiMn x Fe 1-x PO4 is a low-cost material and can also reduce application costs. When the thickness of the positive electrode material layer on one side is too small, for example, less than 22μm, the internal temperature rise of the electrochemical device cannot be effectively increased during the discharge process; when the thickness of the positive electrode material layer on one side is too large, for example, greater than 110μm, the discharge impedance is too large, which will lead to rapid discharge cutoff and shortened discharge time. Therefore, by synergistically regulating the type of positive electrode material, the thickness of the positive electrode material layer on one side and the structure of the positive electrode tab, the advantages of the three can be complementary, the discharge time of the electrochemical device at low temperature and low voltage can be extended, and the electrochemical device can have good discharge performance at low temperature, thereby improving the user experience in the process of using the electrochemical device product. 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% SOC.

[0030] Based on the above research findings, the positive electrode material layer of the electrode assembly provided in this application includes the 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 plate in the electrode assembly of the present application has the above-mentioned structure. By coordinated regulation of the type of positive electrode material, the single-sided thickness of the positive electrode material layer and the structure of the positive electrode ear, the electrochemical device can have good discharge performance at low temperatures, thereby improving the user experience in the process of using the electrochemical device product.

[0031] In some embodiments of the present application, when the number N of positive electrode tabs is multiple, the ratio of the number N of positive electrode tabs to T1 is A, 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 consisting of any two of the above values. By regulating the value of A within the scope of this application, the number of positive electrode tabs matches 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, and compensate for the voltage drop caused by the thick coating technology, thereby further improving the discharge capacity of the electrochemical device.

[0032] In some embodiments of the present application, the thickness of the positive electrode tab is T2 mm. As shown in FIG2 , the width of the positive electrode tab 11 is K2 mm, 0.02≤T2≤1, and 1≤K2≤20. For example, T2 may 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 may 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 regulating the values ​​of T2 and K2 within the scope of this application, the thickness and width of the tabs can be maximized while matching the thickness and width of the overall electrochemical device, thereby minimizing the discharge impedance of the electrochemical device and increasing the initial discharge voltage.

[0033] In some embodiments of the present application, as shown in FIG2 , the width of the positive electrode sheet 10 is K1 mm, the length of the portion of the positive electrode tab 11 located within the positive electrode sheet 10 is L2 mm, and 2≤L2≤K1. Preferably, 2≤L2≤K1 / 2. By regulating 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 the present application, the length of the portion of the positive electrode tab located within the positive electrode sheet matches 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.

[0034] In some embodiments of the present application, as shown in FIG2 , the length of the portion of the positive electrode tab 11 extending beyond the positive electrode sheet 10 is L3 mm, and 2≤L3≤20. For example, L3 may 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 regulating the value of L3 within the scope of the present 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.

[0035] In some embodiments of the present application, the Dv50 of the first positive electrode material is 0.5 μm to 8 μm. For example, the Dv50 of the first positive electrode 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 the present application, the specific surface area of ​​the first positive electrode material is 2 μm. 2 / g to 40m 2 / g. For example, the specific surface area of ​​the first cathode material can be 2m 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 consisting of any two of the above numerical values. In some embodiments of the present application, the gram capacity of the first positive electrode material is 140 mAh / g to 190 mAh / g. Exemplarily, the gram capacity of the first positive electrode 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 consisting of any two of the above numerical values. By regulating the value of at least one of the Dv50, specific surface area or gram capacity of the first positive electrode material within the scope of this application, the electrochemical device can have a higher discharge capacity at a desired low SOC, so that the electrochemical device provided in the present application has a longer discharge time and a higher discharge capacity at low temperatures.

[0036] In this application, Dv50 refers to the particle size at which the volume accumulation reaches 50% of the smallest particle size in the volume-based particle size distribution of the material.

[0037] The present application does not particularly limit the method for regulating the Dv50, specific surface area, and gram capacity of the first positive electrode material, as long as the purpose of the present application can be achieved. For example, by extending the mechanical mixing time, the Dv50 decreases and the specific surface area increases; by shortening the mechanical mixing time, the Dv50 increases and the specific surface area decreases. Generally, when the type of the first positive electrode material remains unchanged, the Dv50 and specific surface area of ​​the first positive electrode material will also affect the gram capacity of the first positive electrode material. In the present application, the Dv50 of the first positive electrode material decreases, the specific surface area increases, and the gram capacity increases; the Dv50 of the first positive electrode material increases, the specific surface area decreases, and the gram capacity of the first positive electrode material decreases.

[0038] In some embodiments of the present 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%. For example, 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 consisting of any two of the above values, and the mass percentage W2 of the second positive electrode material can be 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, 101%, 102%, 103%, 104%, 105%, 106%, 107%, 108%, 109%, 110%, 1110%, 112%, 113%, 114%, 115%, 116%, 117%, 118%, 119%, 120%, 121%, 122%, 123%, 124%, 125%, 126%, 127%, 128%, 129%, 130%, 131%, 7%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89% or a range consisting of any two of the above values, the mass percentage content W3 of the conductive agent can be 1%, 2%, 3%, 4%, 5% or a range consisting of any two of the above values, and the mass percentage content W4 of the binder can be 1%, 2%, 3%, 4%, 5% or a range consisting of any two of the above values. By regulating the mass percentage content 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 have good discharge performance under low temperature conditions while having a high energy density.

[0039] In some embodiments of the present application, the second positive electrode 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 above-mentioned 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 By adjusting the type of the second cathode material within the scope of the present application, the electrochemical device can have good discharge performance under low temperature conditions and high energy density.

[0040] The present application has no particular limitation on the material of the positive electrode tab, as long as it can achieve the purpose of the present application. For example, it can be at least one of pure aluminum or copper alloy plated with nickel.

[0041] The present application has no particular limitation on the positive electrode current collector, as long as the purpose of the present application can be achieved. For example, it may include aluminum foil, aluminum alloy foil or a composite current collector (such as an aluminum-carbon composite current collector).

[0042] The present application has no particular limitation on the thickness of the positive electrode current collector, as long as the purpose of the present application can be achieved. For example, the thickness of the positive electrode current collector is 6 μm to 20 μm.

[0043] Optionally, the positive electrode sheet may further include a conductive layer positioned between the positive electrode current collector and the positive electrode material layer. The present application does not particularly limit the composition of the conductive layer; it may be any commonly used conductive layer in the art. The conductive layer includes a conductive agent and a binder. The present application does not particularly limit the conductive agent and binder in the conductive layer; for example, it may be at least one of the above-mentioned conductive agents and binders.

[0044] In the present 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 "negative electrode material layer 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, or on both surfaces of the negative electrode current collector along its thickness. It should be noted that the "surface" here can refer to the entire surface of the negative electrode current collector or a portion of the surface of the negative electrode current collector. This is not particularly limited in the present application, as long as the objectives of the present application can be achieved.

[0045] The present application has no particular restrictions on the negative electrode current collector, as long as the purpose of the present application can be achieved. For example, it may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foam nickel, foam copper or a composite current collector (such as a carbon-copper composite current collector, a nickel-copper composite current collector, a titanium-copper composite current collector, etc.).

[0046] The present application has no particular restrictions on the material of the negative electrode tab, as long as it can achieve the purpose of the present application. For example, it can be at least one of pure nickel, aluminum-nickel composite strip, copper nickel plating, copper alloy nickel plating, pure copper transition copper nickel plating or copper alloy nickel plating.

[0047] In the present application, the negative electrode material layer includes a negative electrode active material. The negative electrode active material of the present application may include natural graphite, artificial graphite, mesophase microcarbon beads (MCMB), hard carbon, soft carbon, silicon-based active materials, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel structure lithium titanate Li4Ti5O 12 , Li-Al alloy and metallic lithium, etc. For example, the negative electrode active material may include artificial graphite and silicon-based active material, and the mass ratio of artificial graphite and silicon-based active material may be (100 to 0): (0 to 100); the above-mentioned silicon-based active material may include a combination of one or more of SiC, SiO or elemental Si, and the mass ratio of SiC, SiO and elemental Si may be (1 to 0): (0 to 1): (0 to 1). The present application has no special restrictions on the particle size distribution Dv10, Dv50, and Dv90 of the negative electrode active material, as long as the purpose of the present application can be achieved. For example, the Dv10 of the negative electrode active material may be 2μm to 11μm, Dv50 may be 12μm to 20μm, and Dv90 may be 21μm to 28μm. The present application has no special restrictions on the specific surface area of ​​the negative electrode active material, as long as the purpose of the present application can be achieved. For example, the specific surface area of ​​the negative electrode active material may be 0.5m 2 / g to 3m 2 The present application has no particular limitation on the gram capacity of the negative electrode active material, as long as the purpose of the present application can be achieved. For example, the gram capacity of the negative electrode active material can be 400 mAh / g to 1000 mAh / g.

[0048] In this application, Dv10 refers to the particle size at which 10% of the volume is accumulated, measured from the smallest particle size, in the volume-based particle size distribution of the material; and Dv90 refers to the particle size at which 90% of the volume is accumulated, measured from the smallest particle size, in the volume-based particle size distribution of the material.

[0049] The negative electrode material layer also includes a conductive agent and / or a binder. This application does not particularly limit the types of the conductive agent and binder, as long as they can achieve the purpose of this application. For example, it can be at least one of the above-mentioned conductive agents and binders. This application does not particularly limit 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 they can achieve the purpose of this application.

[0050] This application does not impose any particular restrictions on the thickness of the negative electrode material layer, as long as the purpose of this application can be achieved. For example, the thickness of the negative electrode material layer is 30 μm to 150 μm. This application does not impose any particular restrictions on the thickness of the negative electrode current collector, as long as the purpose of this application can be achieved. For example, the thickness of the negative electrode current collector is 3 μm to 16 μm. This application does not impose any particular restrictions on the thickness of the negative electrode pole piece, as long as the purpose of this application can be achieved. For example, the thickness of the negative electrode pole piece is 50 μm to 250 μm.

[0051] Optionally, the negative electrode sheet may further include a conductive layer positioned between the negative electrode current collector and the negative electrode material layer. The present application does not specifically limit the composition of the conductive layer; it may be any commonly used conductive layer in the art. The conductive layer includes a conductive agent and a binder. The present application does not specifically limit the conductive agent and binder in the conductive layer; for example, it may be at least one of the above-mentioned conductive agents and binders.

[0052] In the present application, the electrode assembly also includes a separator to separate the positive electrode plate and the negative electrode plate, prevent internal short circuits in the electrochemical device, allow electrolyte ions to pass freely, and do not affect the electrochemical charge and discharge process. The present application has no particular restrictions on the separator, as long as it can achieve the purpose of the present application. For example, the material of the separator may include but is not limited to polyethylene (PE), polypropylene (PP)-based polyolefins (PO), polyesters (for example, polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex or aramid; the type of separator may include at least one of a woven membrane, a non-woven membrane, a microporous membrane, a composite membrane, a rolled membrane or a spun membrane. For example, the separator may include a substrate layer and a surface treatment layer. The substrate layer may be a non-woven fabric, a membrane or a 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, polypropylene porous film, polyethylene porous film, polypropylene non-woven fabric, polyethylene non-woven fabric or polypropylene-polyethylene-polypropylene porous composite film can be used. Optionally, a surface treatment layer is provided on at least one surface of the substrate layer, and the surface treatment layer can be a polymer layer or an inorganic layer, or a layer formed by a mixed polymer and an inorganic substance. For example, the inorganic layer includes inorganic particles and a binder, and the above-mentioned inorganic particles are not particularly limited, for example, they can include at least one of aluminum oxide, 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 above-mentioned binder is not particularly limited, for example, it can be at least one of the above-mentioned binders. Polymer is included in the polymer layer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinyl pyrrolidone, polyvinyl ether or polyvinylidene fluoride or poly (vinylidene fluoride-hexafluoropropylene).

[0053] The second aspect of the present application provides an electrochemical device, which includes the electrode assembly according to any of the aforementioned embodiments. Therefore, the electrochemical device provided by the present application can maintain good discharge performance under low temperature conditions.

[0054] The electrochemical device of the present application also includes an electrolyte, and the electrolyte includes 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(oxalatoborate) (LiBOB) or lithium difluoroborate. The present application has no particular restrictions on the mass percentage of the lithium salt in the electrolyte, as long as the purpose of the present application can be achieved. The present application has no particular restrictions on the non-aqueous solvent, as long as the purpose of the present application can be achieved, for example, it may include but is not limited to at least one of a carbonate compound, a carboxylate compound, an ether compound or other organic solvents. The above-mentioned carbonate compound may include but is not limited to at least one of a chain carbonate compound, a cyclic carbonate compound or a fluorinated carbonate compound. The above-mentioned linear carbonate compound may include but is not limited to at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC) or methylethyl carbonate (MEC). The above-mentioned cyclic carbonate may include but is not limited to at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) or vinylethylene carbonate (VEC). The above-mentioned fluorocarbonate compound may include but is 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 carboxylate compound may include but is 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, decanoic acid, valerolactone or caprolactone. The ether compound may include but is 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 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-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate or trioctyl phosphate. In the present application, the electrolyte may further include an additive, and the additive may be one or more of fluoroethylene carbonate, a benzene derivative, 1,3-propane sultone, ethyl propionate, adiponitrile, or glutaronitrile.The above-mentioned benzene derivatives can be a combination of one or more of biphenyl, cyclohexylbenzene, tert-amylbenzene, terphenyl, and dibenzofuran, wherein the mass ratio of biphenyl, cyclohexylbenzene, tert-amylbenzene, terphenyl, and dibenzofuran can be (1 to 0):(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 of the electrochemical device known in the art. This application does not limit these other components. This application does not specifically limit the packaging bag and can be any packaging bag known in the art, as long as it can achieve the purpose of this application.

[0056] The electrochemical device of the present application is not particularly limited and may include any device that undergoes an electrochemical reaction. In some embodiments, the electrochemical device may include, but is not limited to, a lithium metal secondary battery, a lithium ion secondary battery (lithium ion battery), a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

[0057] The preparation process of the electrochemical device of the present application is well known to those skilled in the art and is not particularly limited in this application. For example, it may include, but is not limited to, the following steps: stacking the positive electrode sheet, separator, and negative electrode sheet in sequence, and winding, folding, and other operations as needed to obtain a wound electrode assembly, placing the electrode assembly in a packaging bag, injecting an electrolyte into the packaging bag, and sealing the packaging bag to obtain the electrochemical device; or stacking the positive electrode sheet, separator, and negative electrode sheet in sequence, and then securing 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 an electrolyte into the packaging bag, and sealing the packaging bag to obtain the electrochemical device. In addition, as needed, overcurrent protection elements, guide plates, etc. may be placed in the packaging bag to prevent pressure rise and overcharging and discharging inside the electrochemical device. The packaging bag is a packaging bag known in the art and is not limited in this application.

[0058] The third aspect of the present application provides an electrical device, which includes the electrochemical device according to any of the aforementioned embodiments. Therefore, the electrical device provided by the present application has good performance.

[0059] The present application does not particularly limit the type of electrical device, and it can be any electrical device known in the prior art. In some embodiments, the electrical device may include, but is not limited to, a laptop computer, a pen-type computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a headset, a video recorder, an LCD television, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor.

[0060] Example

[0061] The following examples and comparative examples are provided to more specifically illustrate the embodiments of the present invention. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0062] Test methods and equipment:

[0063] Particle size test:

[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 dispersant ethanol. The sample was completely dispersed in the ethanol. After ultrasonic cleaning at 120 W for 30 minutes, the sample was placed in the laser particle size analyzer to measure Dv10, Dv50, and Dv90.

[0065] Specific surface area test:

[0066] According to the national standard “Determination of the specific surface area of ​​solid substances by gas adsorption BET method” (GB / T 19587-2017), the specific surface area of ​​the samples was tested by nitrogen adsorption method using a specific surface area analyzer (model: TristarⅡ3020M).

[0067] Gram Capacity Test:

[0068] In a dry room at 25°C and humidity ≤ 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 thoroughly stirred to form a uniform positive electrode slurry (solid content 75 wt%). This positive electrode slurry was coated onto a 10 μm thick aluminum foil (positive electrode current collector), followed by drying and cold pressing. The slurry was then punched into small discs with a diameter of 14 mm for use 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 button-type half-cell was assembled using the electrolyte described in Example 1.

[0069] Half-cell charge and discharge tests were performed on a LAND CT2001A battery test system. The test was performed at an operating voltage range of 0.01V to 2V and a current density of 10mA / g, and the initial discharge capacity was recorded.

[0070] When the above-mentioned active material is the first positive electrode material, the measured first discharge capacity in grams is the discharge capacity in grams of the first positive electrode material; when the above-mentioned active material is the negative electrode active material (composed of artificial graphite and SiO2 in a mass ratio of 50:50), the measured first discharge capacity in grams is the discharge capacity in grams of the negative electrode active material.

[0071] Low temperature discharge test:

[0072] The lithium-ion battery was placed at 25°C for 5 minutes, discharged at a constant current of 0.5C to 3.0V, and then placed at rest for 5 minutes. It was charged at a constant current of 0.1C for 2 hours and placed at rest for 5 minutes. The lithium-ion battery was then placed in a high and low temperature box at 0°C for 2 hours, and then discharged at a constant current of 1C to 3.0V. The discharge time was recorded as t min.

[0073] Measurement of the length L1 and width K1 of the positive electrode sheet, the thickness T2 and width K2 of the positive electrode tab, the length L2 of the portion of the positive electrode tab located within the positive electrode sheet, and the length L3 of the portion of the positive electrode tab extending beyond the positive electrode sheet:

[0074] Use a ruler to measure the length and width of the positive electrode sheet, the width of the positive electrode ear, the length of the part of the positive electrode ear located inside the positive electrode sheet, and the length of the part of the positive electrode ear extending beyond the positive electrode sheet. Measure three times and take the average value.

[0075] The thickness of the positive electrode tab was measured using a micrometer, and the measurement was repeated three times to obtain the average value.

[0076] Example 1-1

[0077] <Preparation of positive electrode sheet>

[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 thoroughly stirred to form a positive electrode slurry with a solid content of 75 wt%. The positive electrode slurry was evenly coated on one surface of a 10 μm thick aluminum foil and dried at 85°C to obtain a single-sided positive electrode material coating with a thickness of 100 μm. The above steps were repeated on the other surface of the aluminum foil to obtain a double-sided positive electrode material coating. After cold pressing, slitting, and welding a positive electrode tab, the tab was vacuum dried at 85°C for 4 hours to obtain a 74 mm × 867 mm positive electrode sheet for future use. The positive electrode tab is a centrally positioned tab structure made of pure aluminum. The Dv50 of the first positive electrode material is 4.5 μm, and the specific surface area of ​​the first positive electrode material is 18.0 m 2 / g, and the gram capacity of the first positive electrode material is 165mAh / g.

[0079] <Preparation of negative electrode sheet>

[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 stirred thoroughly to produce a negative electrode slurry with a solid content of 40 wt%. The negative electrode slurry was evenly coated on one surface of a 6 μm thick copper foil for the negative electrode current collector and dried at 85°C to produce a negative electrode sheet with a single-sided negative electrode material layer and a thickness of 100 μm. The above steps were repeated on the other surface of the copper foil to produce a negative electrode sheet with a double-sided negative electrode material layer. 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 measuring 78 mm x 875 mm for future use. The negative electrode tab had a centrally positioned tab structure and was made of pure nickel. The negative electrode active material consisted of artificial graphite and SiO in a 50:50 mass ratio. The Dv10 of the negative electrode active material is 4 μm, the Dv50 of the negative electrode active material is 16 μm, the Dv90 of the negative electrode active material is 26 μm, the maximum particle size Dmax of the negative electrode active material is 35 μm, and the specific surface area of ​​the negative electrode active material is 1.5 m 2 / g, and the gram 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 were gradually added and mixed uniformly at a mass ratio of 20:30:30:20 to form a base solvent. Lithium hexafluorophosphate was then added and stirred until completely dissolved to form an electrolyte. The lithium hexafluorophosphate content was 12.5% ​​by mass, with the remainder being the base solvent.

[0083] <Preparation of Separator>

[0084] The coating layer is evenly 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 mixed layer of aluminum oxide and polyvinylidene fluoride (mass ratio is 9:1).

[0085] <Preparation of lithium-ion batteries>

[0086] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator positioned between the positive and negative electrode sheets to provide insulation. The electrodes are then wound to form an electrode assembly. As shown in FIG3 , 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 a first edge 101 and a second edge 102 . 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 thickness T2 of the positive electrode tab, the width K2 of the positive electrode tab, the length L1 of the positive electrode sheet, the width K1 of the positive electrode sheet, the length L2 of the portion of the positive electrode tab located within the positive electrode sheet, and the length L3 of the portion of the positive electrode tab extending beyond the positive electrode sheet are shown in Table 1. The electrode assembly was placed in an outer packaging foil and dehydrated at 80°C, and the prepared electrolyte was injected. After vacuum packaging, standing, formation, shaping, and capacity testing, a lithium-ion battery was obtained.

[0087] Example 1-2

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

[0089] Examples 1-3

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

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

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

[0093] Example 2-1 to Example 2-9

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

[0095] Comparative Example 1

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

[0097] <Preparation of positive electrode sheet>

[0098] In a stirred tank, lithium nickel cobalt manganese oxide (NCM523), conductive carbon black, and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 95:2.5:2.5. N-methylpyrrolidone (NMP) was added and thoroughly stirred to form a positive electrode slurry with a solid content of 70 wt%. The slurry was evenly coated on one surface of a 10 μm-thick aluminum foil and dried at 85°C to produce a single-sided positive electrode sheet with a 100 μm-thick positive electrode material layer. The above steps were repeated on the other surface of the aluminum foil to produce 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 74 mm × 867 mm positive electrode sheet ready for use. The positive electrode tabs were designed with the tabs positioned centrally, and the tabs were made of pure aluminum.

[0099] Comparative Example 2

[0100] Except for preparing the positive electrode sheet according to the following steps, the rest is the same as Example 1-2.

[0101] <Preparation of positive electrode sheet>

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

[0103] Comparative Example 3 to Comparative Example 4

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

[0105] In the above-mentioned Examples 1-2, Examples 1-4 to Examples 1-24 and Comparative Examples 2 to Comparative Examples 4, when the electrode assembly is a wound structure, each layer of the positive electrode sheet is provided with a positive electrode tab, and the relative positions of the positive electrode tabs in the electrode assembly are the same, that is, the distance between the positive electrode tab edge 110 close to the first edge 101 and the first edge 101 is 7 mm, and the distance between the negative electrode tab edge 120 close to the second edge 102 and the second edge 102 is 10 mm, and the width of the electrode assembly (that is, 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 also 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 that 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 that 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 no relevant preparation parameters.

[0110] It can be seen from Examples 1-1 to 1-24 and Comparative Examples 1 to 4 that 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 means that the lithium-ion battery has better discharge performance at low temperatures, thereby improving the user experience in using lithium-ion battery products.

[0111] Specifically, FIG1 is a low-temperature discharge curve diagram of the lithium-ion batteries in Example 1-1 and Comparative Example 1. As can be seen from the figure, the low-temperature discharge time of the lithium-ion battery in Example 1-1 is longer, indicating that the lithium-ion battery in Example 1-1 has better discharge performance at low temperatures.

[0112] The value of the ratio A of the number of positive electrode tabs N to the thickness T1 of the positive electrode material layer on a single side generally affects the low-temperature discharge performance of a lithium-ion battery. 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 has a longer low-temperature discharge time, thereby 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 generally affect the low-temperature discharge performance of a lithium-ion battery. As can be seen from Examples 1-1 to 1-24, when the values ​​of T2 and K2 are within the ranges of this application, the lithium-ion battery has a longer low-temperature discharge time, indicating that the lithium-ion battery has good discharge performance at low temperatures.

[0114] The relationship between the width K1 of the positive electrode tab and the length L2 of the portion of the positive electrode tab located within the positive electrode tab generally affects the low-temperature discharge performance of a lithium-ion battery. As can be seen from Examples 1-1 to 1-24, when the relationship between K1 and L2 falls within the scope of this application, the lithium-ion battery has a longer low-temperature discharge time, thereby demonstrating that the lithium-ion battery has 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 a lithium-ion battery. As can be seen from Examples 1-1 to 1-24, when the value of L3 is within the range of this application, the lithium-ion battery has a longer low-temperature discharge duration, demonstrating that the lithium-ion battery has good discharge performance at low temperatures.

[0116] Table 2

[0117] It can be seen from Examples 2-1 to 2-5 that 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 means that the lithium-ion battery has better discharge performance at low temperatures, thereby improving the user experience in using lithium-ion battery products.

[0118] The mass percentage W1 of the first positive electrode material, the mass percentage W2 of the second positive electrode material, the mass percentage W3 of the conductive agent, and the mass percentage W4 of the binder generally affect the energy density of the 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 ranges of this application, the lithium-ion battery has a longer low-temperature discharge time, thereby demonstrating that the lithium-ion battery has better discharge performance at low temperatures.

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

Claims

1. An electrode assembly comprising at least one positive electrode sheet, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode material layer disposed on two surfaces of the positive electrode current collector, wherein: The positive electrode material layer includes 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 T1 μm, 22≤T1≤110; The length of the positive electrode plate is L1mm; The electrode assembly further comprises at least one positive electrode tab, When the number of the positive electrode tab is one, the positive electrode tab is a tab-center structure; or, When the number of the positive electrode tabs is plural, the ratio of the number of the positive electrode tabs to L1 is B, and 0.002≤B≤0.

01.

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

1.

3. The electrode assembly according to claim 1, wherein: 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.

4. The electrode assembly according to claim 1, wherein: The width of the positive electrode plate is K1 mm, the length of the portion of the positive electrode tab located inside the positive electrode plate is L2 mm, and 2≤L2≤K1.

5. The electrode assembly according to claim 4, wherein: The length of the portion of the positive electrode tab that extends beyond the positive electrode sheet is L3 mm, 2≤L3≤20.

6. The electrode assembly according to claim 1, wherein: The first positive electrode material satisfies at least one of the following characteristics: 1) The 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 2m 2 / g to 40m 2 / g; 3) The gram capacity of the first positive electrode material is 140 mAh / g to 190 mAh / g.

7. The electrode assembly according to claim 1, wherein: The positive electrode material layer also 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%.

8. The electrode assembly according to claim 7, wherein: The second positive electrode material includes at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based material, 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.

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

10. An electrical device comprising the electrochemical device according to claim 9.

Images