Positive electrode sheet, lithium battery, and device

Abstract

The present invention provides a positive electrode sheet, a lithium battery, and a device. The positive electrode sheet comprises a positive electrode current collector, and a bottom coating and a positive electrode coating that are sequentially stacked on at least one side of the positive electrode current collector, wherein the bottom coating contains a first positive electrode lithium supplementing agent, and the positive electrode coating contains a positive electrode active material and a second positive electrode lithium supplementing agent; the first coulombic efficiency of the first positive electrode lithium supplementing agent is less than 30%; and the second positive electrode lithium supplementing agent can decompose to generate gas under a voltage greater than a de-lithiation potential of the second positive electrode lithium supplementing agent. The first positive electrode lithium supplementing agent and the second positive electrode lithium supplementing agent are introduced into the positive electrode sheet at the same time, and are arranged in the layered manner as described above, so that many problems caused by using the two independently can be reduced, and the lithium supplementing utilization rate of the first positive electrode lithium supplementing agent and that of the second positive electrode lithium supplementing agent are improved; and moreover, the battery impedance is not significantly increased, and the battery power performance is improved.

Description

Positive electrode sheet, lithium battery and device

[0001] This disclosure claims priority to the Chinese patent application filed with the China Patent Office on October 31, 2023, with application number 202311440645.2 and application name “Positive Electrode Plate, Lithium Battery and Device,” the entire contents of which are incorporated by reference into this disclosure. Technical Field

[0002] The present disclosure relates to the technical field of lithium-ion batteries, and in particular to a positive electrode sheet, a lithium battery, and a device. Background Art

[0003] During the first charge of a lithium battery, a solid electrolyte film (SEI film for short) forms on the surface of the negative electrode, which consumes the active lithium ions released from the positive electrode and reduces the battery's initial coulombic efficiency and energy density. In order to compensate for the irreversible consumption of active lithium during the first charge, the industry has adopted the measure of pre-adding a lithium replenisher that can provide active lithium ions into the lithium battery. Battery lithium replenishment methods are generally divided into positive electrode lithium replenishment and negative electrode lithium replenishment. Compared with the negative electrode lithium replenishment method of directly pressing chemically active metallic lithium with the negative electrode to achieve pre-lithiation, positive electrode lithium replenishment is safer and more compatible with existing battery preparation processes.

[0004] Among them, positive electrode lithium replenishment technology involves introducing positive electrode lithium replenishers with high reversible lithium removal capacity into the battery's positive electrode. Positive electrode lithium replenishers are mainly divided into two categories. The first category is lithium-rich materials with extremely low initial coulombic efficiency. After releasing lithium ions at a certain voltage, a portion of the main structure or delithiation products remains on the positive electrode side. The second category is sacrificial lithium replenishers that decompose at a certain voltage to produce lithium ions and gas. However, the use of either type of positive electrode lithium replenisher in lithium batteries alone presents certain problems. For example, mixing all positive electrode active materials with the first type of positive electrode replenisher in a single layer will significantly increase the liquid-phase diffusion impedance of the positive electrode and reduce the battery's power performance. For example, the positive electrode coating formed by mixing the second type of positive electrode replenisher with the positive electrode active materials is in direct contact with the positive electrode current collector. The gases generated by the decomposition of this type of replenisher are difficult to discharge smoothly. The residual gas reduces its utilization rate, increases battery impedance, and reduces battery power performance.

[0005] Therefore, it is necessary to develop a technical solution that can effectively improve the lithium replenishment effect of the positive electrode without affecting the electrochemical performance of the lithium battery after lithium replenishment.

[0006] Summary of the Invention

[0007] In view of this, the present disclosure introduces the above-mentioned lithium supplement material with low coulombic efficiency and the lithium supplement material that can decompose and produce gas into the battery positive electrode. By rationally distributing the two materials, the negative effects of using only one lithium supplement can be reduced, so that the utilization rate of these two types of lithium supplements can be fully utilized, while not significantly increasing the battery impedance and improving the battery power performance.

[0008] Specifically, the first aspect of the present disclosure provides a positive electrode plate, including a positive electrode current collector and a coating structure arranged on at least one side of the positive electrode current collector, the coating structure including a first lithium replenishing layer, a positive electrode active material layer and a second lithium replenishing layer stacked in sequence, and the first lithium replenishing layer is close to the positive electrode current collector; wherein, the first lithium replenishing layer includes a first positive electrode lithium replenishing agent, the positive electrode active material layer includes a first positive electrode active material, and the second lithium replenishing layer includes a second positive electrode lithium replenishing agent and a second positive electrode active material, wherein the first coulombic efficiency of the first positive electrode lithium replenishing agent is less than 30%, and the second positive electrode lithium replenishing agent can decompose to release lithium ions and generate gas.

[0009] In the above-mentioned positive electrode plate of the embodiment of the present disclosure, the first positive electrode lithium replenisher and the second positive electrode lithium replenisher are introduced at the same time, and they are layered as above, and a positive electrode active material layer is arranged between the two lithium replenisher layers containing the two respectively. This can ensure the high structural stability of the overall coating structure, and can reduce many problems caused by the use of these two positive electrode lithium replenishers alone, and can improve their lithium replenishment utilization rate, effectively improve the energy density of the battery, and at the same time, the battery has low impedance and good power performance.

[0010] In a second aspect, the present disclosure provides a lithium battery, comprising the positive electrode sheet as described in the first aspect of the present disclosure.

[0011] Due to the use of the above-mentioned positive electrode plate, the utilization rate of the two types of lithium supplements in the lithium battery is high, the total amount of reversible lithium in the battery is high, the energy density is improved, and the battery impedance is low and the power performance is good.

[0012] In a third aspect, the present disclosure provides a device comprising the lithium battery described in the second aspect of the present disclosure, which device is an electrical device or an energy storage system. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIG1A and FIG1B are schematic structural diagrams of a positive electrode plate provided by the present disclosure.

[0014] FIG2 is another schematic diagram of the structure of the positive electrode plate provided by the present disclosure. DETAILED DESCRIPTION

[0015] The technical solutions of the embodiments of the present disclosure will be described below with reference to the accompanying drawings.

[0016] Referring to Figures 1A and 1B , an embodiment of the present disclosure provides a positive electrode sheet 100 comprising a positive current collector 10 and a coating structure 20 disposed on at least one side of the positive current collector 10. The coating structure 20 comprises a first lithium replenishing layer 21, a positive electrode active material layer 22, and a second lithium replenishing layer 23 stacked in sequence, with the first lithium replenishing layer 21 being adjacent to the positive current collector 10. The first lithium replenishing layer 21 comprises a first positive electrode lithium replenishing agent 210, and the positive electrode active material layer 22 comprises a first positive electrode active material 221. The second lithium replenishing layer 23 comprises a second positive electrode lithium replenishing agent 230 and a second positive electrode active material 231. The first positive electrode lithium replenishing agent 210 has a first coulombic efficiency of less than 30%. The second positive electrode lithium replenishing agent 230 can decompose to release lithium ions and generate gas.

[0017] The above-mentioned positive electrode plate 100 contains two types of positive electrode lithium replenishers at the same time. The first positive electrode lithium replenisher 210 with low initial coulombic efficiency is arranged close to the positive electrode current collector 10 as a base coat, and the positive electrode active material layer 22 is arranged thereon. This can increase the bonding force between the positive electrode active material layer 22 and the positive electrode current collector 10 and improve the peeling force of the plate. At the same time, due to the coverage of the first lithium replenisher layer 21 containing the first positive electrode lithium replenisher 210 by the positive electrode active material layer 22, the moisture absorption rate of the first positive electrode lithium replenisher 210 with high water absorption can be reduced, thereby increasing the control requirements for environmental humidity during the preparation of the positive electrode plate 100, reducing the equipment investment required for humidity control, and reducing manufacturing costs. In addition, compared with the electrode sheet in which the lithium replenishing material is only the first positive electrode lithium replenishing agent, when the total lithium replenishing amount remains unchanged, the amount of the first positive electrode lithium replenishing agent added to the positive electrode sheet of the present invention is lower. Even when the first lithium replenishing layer 21 still contains positive electrode active material, the reduction in the electrode sheet compaction density brought about by it is also smaller, the battery impedance is relatively low, and the power is relatively better.

[0018] The layer containing the second positive electrode lithium replenisher 230 that can decompose and produce gas and the positive electrode active material is placed away from the positive electrode current collector 10, that is, located on the surface of the positive electrode plate 100. The discharge path of the gas released by the decomposition of the second positive electrode lithium replenisher 230 is shortened, which is more conducive to gas discharge. In this way, the probability of battery polarization is reduced during its decomposition process, and its decomposition ratio and utilization rate are improved. At the same time, less gas remains in the positive electrode plate 100, and the battery impedance is also reduced. In addition, after its decomposition, the porosity of the second lithium replenisher layer 23 can be increased, which ultimately improves the battery's high-power discharge capability and continuous discharge capability.

[0019] In the present disclosure, the second positive electrode lithium replenisher can only decompose and release lithium ions. Because after it decomposes and releases lithium ions and gas, the main structure is no longer there, but the lithium ions cannot be inserted back into it. This type of lithium replenisher can also be called a sacrificial lithium replenisher. After the first positive electrode lithium replenisher releases lithium ions at a higher voltage, a part of the main structure or delithiation products remains in the positive electrode, and it has a certain ability to insert lithium ions back, but its ability to insert lithium ions back is poor, that is, its ability to reversibly remove / insert lithium ions is poor, and the first coulombic efficiency is low (less than 30%), which is much lower than the first coulombic efficiency of conventional positive electrode active materials (generally above 60%). Among them, the first coulombic efficiency of the first positive electrode lithium replenisher can be obtained by the ratio of the first cycle discharge capacity to the first cycle charge capacity of a button battery made with it as the positive electrode active material. Specifically, the test conditions for the first coulombic efficiency of the first positive electrode lithium replenisher are: buckled battery specification CR2032, the positive electrode foil is carbon-coated aluminum foil, the positive electrode formula is lithium replenisher: conductive agent: binder = 8:1:1 (mass ratio), the negative electrode is a metal lithium sheet, the separator is a PP separator with a thickness of 14μm, the electrolyte is 1M LiPF6 dissolved in a mixed solvent of EC / DMC / DEC / EMC = 1:1:1:1 (volume ratio), 0.1C charge to 4.5V, 0.1C discharge to 2.0V, the first cycle discharge capacity / first cycle charge capacity is the first coulombic efficiency.

[0020] In the embodiment of the present disclosure, the first positive electrode lithium replenisher 210 can be selected from one or more of Li6CoO4, Li2MoO3, Li5FeO4, Li6MnO4, Li2NiO2, Li2CuO2, Li3PO4, Li4SiO4, Li2SiO3, Li3VO4, Li2VO3, Li5ReO6, Li2RuO3, Li2MnO3, Li2MoO3, Li2S, LiF, etc., but is not limited thereto. The surface of the first positive electrode lithium replenisher may or may not have a conductive coating layer, preferably having a conductive coating layer. In the embodiment of the present disclosure, the second positive electrode lithium replenisher 230 can be selected from one or more of Li2CO3, Li3N, Li2O2, Li2O, Li2C2O4, Li2C4O4, Li2C3O5, Li2C4O6, etc., but is not limited thereto.

[0021] It should be noted that the first positive electrode active material 221 and the second positive electrode active material 231 may be the same or different positive electrode active materials. For the convenience of description in this disclosure, they are distinguished by different names / codes. In the embodiment of the present disclosure, each positive electrode active material may be selected from one or more of lithium iron phosphate (LFP), lithium manganese iron phosphate (LMFP), lithium manganate (LMO), lithium cobaltate, lithium nickel manganate material (LNMO), nickel cobalt manganate ternary material (NCM), nickel cobalt aluminum ternary material (NCA), lithium-rich lithium manganate material, etc. These positive electrode active materials may be undoped or modified by doping, and their surfaces may have a conductive coating or not have a conductive coating. Generally, materials of lithium iron phosphate and lithium manganese iron phosphate usually have a conductive carbon coating.

[0022] In the present disclosure, the first lithium replenishing layer 21 may not contain a positive electrode active material (as shown in FIG1A ), or may contain a positive electrode active material (as shown in FIG1B , which may be indicated by reference numeral 211 ). The material selection range of the positive electrode active material 211 may refer to the description of the first positive electrode active material 221 and the second positive electrode active material 231 in the previous text of the present disclosure.

[0023] In some embodiments of the present disclosure, the first lithium replenishing layer 21 includes a third positive electrode active material having a mass percentage not exceeding (i.e., less than or equal to) that of the first positive electrode lithium replenishing agent. By not including too much of the third positive electrode active material, the reduction in the positive electrode sheet's compaction density caused by its co-layer distribution with the first positive electrode lithium replenishing agent 210 can be minimized, resulting in relatively low battery impedance and improved power.

[0024] In some embodiments of the present disclosure, the first lithium replenishing layer 21 may include the following components in percentage by weight: 50%-90% of the first positive electrode lithium replenishing agent 210, 0-40% of the third positive electrode active material, 0.5-10% of the binder, and 0.5-10% of the conductive agent. The presence of no more than 40% by weight of the third positive electrode active material is more conducive to ensuring a high compaction density of the positive electrode sheet and low battery impedance. The presence of an appropriate amount of binder can ensure the adhesion of the first lithium replenishing layer 21 to the positive electrode current collector 10, and the presence of an appropriate amount of conductive agent helps to improve the electronic conductivity of the first lithium replenishing layer 21. Specifically, the mass percentage of the first positive electrode lithium replenishing agent 210 in the first lithium replenishing layer 21 can be 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, or 90%, etc. The mass percentage of the binder or conductive agent can be 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 4%, 4.5%, 5%, 6%, 7%, 8% or 9%, etc.

[0025] In some embodiments of the present disclosure, the first lithium-replenishing layer 21 contains a third positive electrode active material, the mass percentage of which can be 10-40%, for example, 12%, 15%, 20%, 25%, 28%, 30%, 35%, or 40%. The inclusion of an appropriate amount of the third positive electrode active material in the first lithium-replenishing layer 21 allows the first lithium-replenishing layer 21 to contribute a certain amount of capacity to the battery after formation. Furthermore, the inclusion of the positive electrode active material in the first lithium-replenishing layer 21 facilitates controlling coating accuracy and improving process stability.

[0026] In some other embodiments of the present disclosure, the first lithium replenishing layer 21 does not contain the third positive electrode active material, that is, the content of the third positive electrode active material in the first lithium replenishing layer 21 is zero. In this case, it can still be considered that the mass percentage of the first positive electrode lithium replenishing agent 210 in the first lithium replenishing layer 21 is greater than the mass percentage of the third positive electrode active material (that is, the mass percentage of the third positive electrode active material in the first lithium replenishing layer is less than or equal to the mass percentage of the first positive electrode lithium replenishing agent). The absence of the third positive electrode active material in the first lithium replenishing layer 21 can make the viscosity of the slurry used to form the first lithium replenishing layer 21 more suitable, making coating easier, and increasing the compaction density of the positive electrode sheet, thereby avoiding reducing battery impedance and power performance.

[0027] In some embodiments of the present disclosure, the content of the positive electrode lithium replenisher in the positive electrode active material layer 22 is less than or equal to 1%. In some embodiments of the present disclosure, the positive electrode lithium replenisher may not be present in the positive electrode active material layer 22. This can avoid the slurry coating difficulties caused by placing the positive electrode active material and the positive electrode lithium replenisher in the same layer, and the problem of reduced electrode sheet compaction density caused by poor particle size matching between the two.

[0028] In some embodiments of the present disclosure, the ratio of the single-surface density of the first lithium replenishing layer 21 to the single-surface density of the coating structure 20 is 0.01-0.2. This can not only enable the first positive electrode lithium replenishing agent to achieve a good lithium replenishing effect, but also ensure that the reversible capacity of the battery is high, and thus the energy density is high. In some embodiments of the present disclosure, the ratio of the single-surface density of the positive electrode active material layer 22 to the single-surface density of the coating structure 20 is 0.1-0.9; in some embodiments of the present disclosure, the ratio of the single-surface density of the second lithium replenishing layer 23 to the single-surface density of the coating structure 20 is 0.1-0.9. This is conducive to ensuring that the preparation process of the above-mentioned positive electrode plate is highly feasible, the plate structure is highly stable, and at the same time, the compaction density of the plate is high, and the energy density of the battery is high. Taking the first lithium replenishing layer 21 as an example, the "single-sided surface density" here refers to the surface density of the first lithium replenishing layer 21 on one side of the positive electrode current collector 10, rather than the sum of the surface densities of the two first lithium replenishing layers 21 located on both sides of the positive electrode current collector 10; also taking the first lithium replenishing layer 21 as an example, the ratio of the single-sided surface density of the first lithium replenishing layer to the single-sided surface density of the coating structure refers to the ratio of the surface density of the first lithium replenishing layer 21 on one side of the positive electrode current collector 10 to the surface density of the coating structure on that side.

[0029] In some embodiments of the present disclosure, the single-surface density of the first lithium supplement layer 21 can be 0.5-20 g / m 2 This ensures that the amount of the first positive electrode lithium replenisher added is appropriate, ensures that its lithium replenishing capacity is appropriate, and the overall performance of the lithium battery is better. In some embodiments, the single surface density of the first lithium replenishing layer 21 is 1-20g / m 2 , for example, 1.5g / m 2 , 2g / m 2 , 3g / m 2 , 4g / m 2 , 5g / m 2 , 6g / m 2 , 7g / m 2 , 8g / m 2 , 9g / m 2 , 10g / m 2 , 12g / m 2 , 15g / m 2 , 16g / m 2 , 18g / m 2 This is more conducive to the battery to achieve both high positive electrode capacity and initial coulombic efficiency, as well as high lithium supplement utilization rate. In the embodiment of the present disclosure, the single surface density of the positive electrode active material layer 22 and the second lithium supplement layer 23 is 10-500g / m 2 In the range of, for example, specifically 25g / m 2 , 30g / m 2 , 50g / m 2 , 80g / m2 , 100g / m 2 , 150g / m 2 , 200g / m 2 , 210g / m 2 , 220g / m 2 , 250g / m 2 , 300g / m 2 , 350g / m 2 , 400g / m 2 , 450g / m 2 In some embodiments, the single-surface density of the positive electrode active material layer 22 and the second lithium supplement layer 23 is 100-500 g / m 2 This is more conducive to their role in providing capacity in the battery after formation.

[0030] In some embodiments of the present disclosure, the single-sided areal density of the positive electrode active material layer 22 and / or the second lithium replenishing layer 23 is greater than that of the first lithium replenishing layer 21. The positive electrode active material layer 22 and the second lithium replenishing layer 23 are the main capacity-providing layers of the battery, and their single-sided areal density is higher than that of the first lithium replenishing layer 21. This helps ensure high energy density and discharge capacity of the battery. Accordingly, the single-sided thickness of the positive electrode active material layer 22 and / or the second lithium replenishing layer 23 is greater than the single-sided thickness of the first lithium replenishing layer 21. In the embodiments of the present disclosure, the single-sided thickness of the first lithium replenishing layer 21 can be in the range of 0.1-100 μm. In some embodiments, the thickness of the first lithium replenishing layer 21 on a single surface is 1-20 μm, for example, 1.0 μm, 2.0 μm, 3.0 μm, 4.0 μm, 5.0 μm, 6.0 μm, 7.0 μm, 8.0 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, etc. The thinner first lithium replenishing layer 21 helps ensure the stable presence of the positive electrode active material layer 22 on the positive electrode current collector 10 without reducing the reversible capacity of the positive electrode plate 100 or the energy density of the battery cell. At the same time, it ensures that it contains an appropriate amount of the first positive electrode lithium replenishing agent 210, thereby ensuring that the gas production of the positive electrode plate is low during the first charge of the battery. In the embodiment of the present disclosure, the thickness of the positive electrode active material layer 22 or the second lithium replenishing layer 23 on a single surface is 20-200 μm, respectively. An appropriately thick positive electrode active material layer 22 or second lithium replenishing layer 23 can ensure a high energy density and discharge capacity of the battery.

[0031] In some embodiments of the present disclosure, the ratio of the single-surface areal density of the positive electrode active material layer 22 to the second lithium replenishing layer 23 is within a range of 0.5-2.0. By adjusting the areal density ratio of the positive electrode active material layer 22 to the second lithium replenishing layer 23, the mass ratio of the positive electrode active material and the second positive lithium replenishing agent can be adjusted to meet the different requirements of different batteries for energy density, power density, cycle life, etc. Specifically, the ratio can be 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, or 1.9, etc.

[0032] In some embodiments of the present disclosure, in the second lithium replenishing layer 23, the total mass percentage of the second positive electrode active material 231 is greater than the total mass percentage of the second positive electrode lithium replenishing agent 230. This ensures that after the second lithium replenishing layer 23 produces gas during the battery completion process, it will not excessively affect the overall capacity providing function of the second lithium replenishing layer 23. In some embodiments of the present disclosure, in the second lithium replenishing layer 23, the total mass of the second positive electrode lithium replenishing agent is 0.5%-10% of the total mass of the positive electrode active material, for example, specifically 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8% or 9%. This ensures that the second positive electrode lithium replenishing agent 230 replenishes the irreversible consumption of active lithium in the battery while reducing the gas production and increasing the reversible capacity of the battery positive electrode. In some embodiments, this mass percentage is 1-5%.

[0033] In some embodiments of the present disclosure, the total mass proportion of the second positive electrode active material 231 in the second lithium replenishing layer 23 is greater than 80%, preferably greater than 90%. This is conducive to ensuring a high reversible capacity provided by the second lithium replenishing layer 23, and thus ensuring a high reversible capacity of the entire positive electrode sheet.

[0034] In the disclosed embodiment, the second lithium replenishing layer 23 can be a single layer (as shown in FIG. 1A and FIG. 1B ) or multiple layers (i.e., the number of layers is ≥ 2, as shown in FIG. 2 ). When the second lithium replenishing layer 23 is a single layer (as shown in FIG. 1A and FIG. 1B ), the second lithium replenishing agent 230 can be uniformly dispersed in the second positive electrode active material 231 .

[0035] In some embodiments of the present disclosure, when the second lithium replenishing layer 23 is multi-layered, as shown in FIG2 , it may include n second lithium replenishing sub-layers, where n ≥ 2. Each second lithium replenishing sub-layer contains a second positive electrode lithium replenishing agent 230 and a second positive electrode active material 231. The mass ratio of the second lithium replenishing agent 230 to the second positive electrode active material 231 in each second lithium replenishing sub-layer increases from the positive electrode current collector 10 toward the first lithium replenishing layer 21 (in the direction indicated by the arrow in FIG2 ).

[0036] For example, from the positive electrode current collector 10 to the first lithium replenishing layer 21, each sublayer of the second lithium replenishing layer 23 can be sequentially recorded as L1, L2, ..., L n In this way, the surface of the positive electrode current collector 10 is sequentially provided with a first lithium replenishing layer 21, a first sublayer L1 of the second lithium replenishing layer, a second sublayer L2 of the second lithium replenishing layer, ..., an nth sublayer L n The mass ratio of the second positive electrode lithium replenisher 230 to the second positive electrode active material 231 in the first sub-layer L1 is recorded as X1, the mass ratio of the second positive electrode lithium replenisher 230 to the second positive electrode active material 231 in the second sub-layer L2 is recorded as X2, ..., the mass ratio of the second positive electrode lithium replenisher 230 to the second positive electrode active material 231 in the nth sub-layer L n The mass ratio of the second positive electrode lithium supplement 230 and the second positive electrode active material 231 is recorded as X n , then, the above increasing trend can be expressed as: X1≤X2≤X3…≤X n , and X n >X1, X1>0, the specific step-by-step gradient increase method can be: first increase - then keep unchanged - then increase, or keep unchanged first and then increase in sequence, or keep unchanged first - then increase - then keep unchanged - then increase, etc.; it can also be a step-by-step increase method (such as X1<X2<X3…<X n , X1>0).

[0037] The second positive lithium replenisher 230 decomposes at a voltage greater than its delithiation potential to produce active lithium ions to replenish the battery, while also releasing gas. Therefore, after decomposition, it can leave pores at its original location, increasing the porosity of each second lithium replenisher sublayer. The present disclosure controls the mass ratio of the second positive lithium replenisher to the second positive active material in each second lithium replenisher sublayer to increase in a direction away from the positive current collector 10. This is more conducive to constructing a smoother exhaust channel, especially facilitating the smooth discharge of gas generated by the decomposition of the second positive lithium replenisher 230 in the second lithium replenisher sublayer near the positive current collector, reducing battery polarization, and ensuring that the delithiation potential of the second positive lithium replenisher in each second lithium replenisher sublayer is substantially consistent. Consequently, the decomposition ratio of the second positive lithium replenisher in each sublayer is relatively high. The reduced battery polarization also helps reduce the overall impedance of the battery and improve the battery's sustainable discharge capability. Furthermore, after decomposition of this type of lithium-replenishing agent, the pores created in each second lithium-replenishing sublayer also form a gradient pore structure. Specifically, the second lithium-replenishing sublayers closer to the positive electrode current collector 10 have fewer pores and a lower porosity, while the porosity of the second lithium-replenishing sublayers farther away from the positive electrode current collector 10 increases. This gradient pore structure helps increase the overall porosity of the positive electrode sheet 100 and reduce its pore tortuosity, thereby reducing the overall impedance of the battery and improving its power performance.

[0038] In some embodiments, the aforementioned increasing trend occurs layer by layer. That is, within the n-layer second lithium-replenishing sub-layers, the mass ratio of the second lithium-replenishing agent 230 to the second positive electrode active material 231 in each second lithium-replenishing sub-layer increases layer by layer, from the positive electrode current collector 10 toward the first lithium-replenishing layer 21. This facilitates the smoother discharge of gases generated by the decomposition of the second positive electrode lithium-replenishing agent in the second lithium-replenishing layer 23. Furthermore, after decomposition, the second lithium-replenishing layer 23 is endowed with a pore structure in which the porosity increases in the direction of the arrow, further contributing to lowering battery impedance.

[0039] In some embodiments of the present disclosure, among the n-layer second lithium-supplementing sub-layers, at least two adjacent layers satisfy the following conditions: m / (D m / D m-1 )-A m-1 ≥5%; among them, A m-1 A is the mass ratio of the second positive electrode lithium replenishing agent in the m-1th second lithium replenishing sub-layer to the total second positive electrode lithium replenishing agent in the second lithium replenishing layer 23, m is the mass ratio of the second positive electrode lithium replenishing agent in the mth second lithium replenishing sub-layer to the total second positive electrode lithium replenishing agent in the second lithium replenishing layer 23, D m-1 is the thickness of the second lithium-replenishing sublayer (m-1), D m is the thickness of the mth second lithium replenishing sublayer, m is any integer from 2 to n; on the same side of the positive electrode current collector, the m-1th second lithium replenishing sublayer is closer to the positive electrode current collector than the mth second lithium replenishing sublayer. That is, when the thickness of each second lithium replenishing sublayer is substantially the same, at least two adjacent layers of the 1st to nth second lithium replenishing sublayers satisfy A m -A m-1 ≥5%, m is an integer between 2 and n. In this way, after the second positive electrode lithium replenishing agent decomposes, the porosity of at least two adjacent second lithium replenishing sublayers can be clearly distinguished, and the above-mentioned gradient pore structure has a better effect of reducing battery impedance and improving power performance. Further, in some embodiments of the present disclosure, among the n layers of second lithium replenishing sublayers, any two adjacent second lithium replenishing sublayers meet the following conditions: A m / (D m / D m-1 )-A m-1 ≥5%. In some embodiments, A m / (D m / D m-1 )-A m-11 ≥10%, for example, 10%, 15%, 20%, 25%, 30%, 40%, 50%, or 60%, etc.

[0040] In some embodiments, when the thickness of each second lithium-replenishing sub-layer is equal (ie, D m / D m-1=1), in the n-layer second lithium replenishing sub-layer, the difference in mass proportion between the second positive electrode lithium replenishing agent in any two adjacent second lithium replenishing sub-layers and the total second positive electrode lithium replenishing agent in the second lithium replenishing layer 23 is greater than 5%. In other words: m / D m-1 = 1, among the n second lithium-replenishing sub-layers, any two adjacent second lithium-replenishing sub-layers satisfy: A m -A m-1 ≥5%, where m is any integer from 2 to n. Thus, after battery formation is completed, the porosity formed in the second lithium replenishing layer 23 increases layer by layer in a direction away from the positive electrode active material layer 22, which is more effective in reducing battery impedance and improving power performance.

[0041] For example, if the mass ratio of the second positive electrode lithium replenishing agent in the first sublayer L1 of the second lithium replenishing layer 23 to the mass ratio of the second positive electrode lithium replenishing agent in the second lithium replenishing layer 23 is recorded as A1, the mass ratio of the second positive electrode lithium replenishing agent in the second sublayer L2 to the mass ratio of the second positive electrode lithium replenishing agent in the second lithium replenishing layer 23 is recorded as A2, ..., the mass ratio of the second positive electrode lithium replenishing agent in the nth sublayer L n The mass ratio of the second positive electrode lithium replenishing agent to the second lithium replenishing agent in the second lithium replenishing layer 23 is recorded as A n , when the thickness of each second lithium-replenishing sub-layer is equal, then |A2-A1|, |A3-A2|, ... |A n -A n-1 |are all ≥5%, preferably ≥10%. Wherein, A1 is greater than 0. If the total mass of all the second positive electrode lithium replenishing agents in the second lithium replenishing layer 23 is recorded as M, the mass of the second positive electrode lithium replenishing agent in the first sublayer L1 is recorded as m1, the mass of the second positive electrode lithium replenishing agent in the second sublayer L2 is recorded as m2, ..., the mass of the second positive electrode lithium replenishing agent in the nth sublayer L n The mass of the second positive electrode lithium supplement is recorded as m n , then the above A1=m1 / M, A2=m2 / M, ..., A n =m n / M. In some embodiments, when n=2, A1=20%, A2=80%; or A1=30%, A2=70%; or A1=40%, A2=60%; or A1=45%, A2=55%. When n=3, A1=23%, A2=33%, A3=44%; or A1=20%, A2=30%, A3=50%; or A1=10%, A2=30%, A3=60%.

[0042] In the embodiment of the present disclosure, the mass proportion of the second positive electrode active material in each second lithium replenishing sub-layer is more than 80%, preferably more than 90%. This can be more conducive to the higher reversible capacity provided by each second lithium replenishing sub-layer, thereby ensuring that the reversible capacity of the overall positive electrode sheet is higher. In addition, in some embodiments of the present disclosure, the single-sided surface density of each positive electrode sub-coating can be equal or unequal. Among them, taking the first sub-layer L1 of the second lithium replenishing layer 23 as an example, specifically, the ratio of the mass of the second positive electrode active material in the first sub-layer L1 to the total mass of the first sub-layer L1 is more than 80%, and further more than 90%.

[0043] In some embodiments of the present disclosure, n=2, and X2>X1. That is, the second lithium-replenishing layer 23 includes two second lithium-replenishing sublayers, wherein the mass ratio of the second lithium-replenishing agent 230 and the second positive electrode active material 231 in the second lithium-replenishing sublayer farther from the positive electrode current collector 10 is greater than the mass ratio of the second lithium-replenishing agent 230 and the second positive electrode active material 231 in the second lithium-replenishing sublayer closer to the positive electrode current collector 10. This ensures that the second lithium-replenishing layer 23 has the aforementioned effects while being more convenient and time-saving to prepare.

[0044] In addition, it should be noted that the first lithium replenishing layer 21 may also be a multilayer with a gradient composition change; and the positive electrode active material layer 22 may also be a multilayer with a gradient composition change.

[0045] In the present disclosure, the positive electrode active material layer 22 and the second lithium replenishing layer 23 may further contain a conductive agent and a binder, respectively. The conductive agent in each of the above coatings may be selected from one or more of conductive carbon black (such as acetylene black, Ketjen black, Super P, 350G carbon black, etc.), carbon nanotubes (such as single-walled carbon nanotubes or multi-walled carbon nanotubes), graphene, graphite sheets, etc. The binder in each of the above coatings may be selected from one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyolefins (such as polyethylene (PE), polypropylene (PP)), polyacrylonitrile (PAN), polyacrylic acid (PAA), polyimide (PI), styrene-butadiene rubber (SBR), sodium carboxymethyl cellulose (CMC), sodium alginate (SA), gelatin, and a composite binder made of poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) (PEDOT:PSS), but is not limited thereto. In some embodiments, the first lithium replenishing layer 21, the positive electrode active material layer 22, and the second lithium replenishing layer 23 may further contain one or more of a dispersant. The dispersants may be selected from one or more of polyvinyl pyrrolidone (PVP), polyvinyl alcohol (PVA), and the like.

[0046] In the present disclosure, the positive electrode current collector 10 may include, but is not limited to, aluminum foil, aluminum alloy foil, a polymer film coated with aluminum, or the aforementioned materials with a carbon coating on the surface. In some embodiments of the present disclosure, the positive electrode current collector 10 is aluminum foil. In the present disclosure, a coating structure 20 may be formed on one surface of the positive electrode current collector 10 (as shown in Figures 1A, 1B, and 2), or a coating structure 20 may be formed on both opposite surfaces of the positive electrode current collector 10.

[0047] The first lithium replenishing layer 21 can be formed by coating a primer slurry containing a first positive electrode lithium replenishing agent, a conductive agent, a binder, and a solvent, followed by baking. The positive electrode active material layer 22 can be formed by coating a positive electrode slurry containing a first positive electrode active material, a conductive agent, a binder, and a solvent, followed by baking. The coating method can include, but is not limited to, a combination of one or more methods such as spin coating, brush coating, spray coating, dip coating, and scraping. Similarly, the second lithium replenishing layer 23 can be formed by coating a second lithium replenishing slurry containing a second positive electrode lithium replenishing agent, a second positive electrode active material, a conductive agent, a binder, and a solvent, followed by baking. The type of second lithium replenishing slurry used corresponds to the total number of sublayers of the second lithium replenishing layer 23.

[0048] The solvents contained in each slurry may be the same or different, and may be selected from one or more of pyrrolidones (such as N-methylpyrrolidone (NMP), N-ethylpyrrolidone, etc.), cyclic ethers (such as tetrahydrofuran, methyltetrahydrofuran), dimethyl sulfoxide, ketones (such as acetone, butanone), lactones (such as butyrolactone, caprolactone), etc., but are not limited thereto. The solid content of each slurry is not particularly limited, as long as it can meet the fluidity and uniformity of the slurry coating. Generally, the solid content of the primer slurry can be 10-50%. The solid content of the positive electrode slurry is in the range of 30%-70%.

[0049] In addition, each slurry can be applied simultaneously or sequentially in a stacked manner, or applied on the coating formed by drying the previous slurry. Taking the case where the second lithium replenishing layer 23 is a layer as an example, a second lithium replenishing slurry can be directly applied on the positive electrode slurry (can be applied simultaneously or sequentially), and then dried together to remove the solvent, and then rolled. If double-sided coating is required, the above operation can be repeated on the other side surface of the positive electrode current collector 10. Alternatively, the above-mentioned primer slurry can be applied on one side surface of the positive electrode current collector 10 and dried to form the first lithium replenishing layer 21, and then the positive electrode slurry can be applied on the first lithium replenishing layer 21 and dried to form the positive electrode active material layer 22, and then the second lithium replenishing slurry can be applied on the positive electrode active material layer 22 to dry to form the second lithium replenishing layer 23, and then rolled.

[0050] The embodiment of the present disclosure further provides a lithium battery, which includes the positive electrode plate 100 described above in the embodiment of the present disclosure.

[0051] In some embodiments of the present disclosure, a lithium battery includes a positive electrode sheet, a negative electrode sheet, and a separator and an electrolyte disposed between the negative electrode sheet and the positive electrode sheet.

[0052] Among them, the negative electrode plate generally includes a negative electrode current collector and a negative electrode material layer provided on the surface of at least one side of the negative electrode current collector. The negative electrode material layer generally contains a negative electrode active material, a conductive agent, and a binder. In the embodiment of the present disclosure, the negative electrode active material can be selected from one or more of carbon materials, silicon-based materials, tin-based materials, etc. Among them, the carbon material includes one or more of soft carbon, hard carbon, graphite, mesophase carbon microbeads, etc. The silicon-based material may include one or more of elemental silicon, silicon alloy, silicon oxide, silicon-carbon composite material, etc. The tin-based material may include one or more of elemental tin, tin oxide, tin-based alloy, tin-carbon compound, etc.

[0053] The separator is used to separate the positive and negative electrode sheets, maintaining insulation and fluid retention between them. Together, the separator, the positive and negative electrode sheets form the battery cell, which is housed in a battery casing and is soaked in electrolyte. In some embodiments of the present disclosure, the lithium battery can be assembled by the following method: stacking the positive electrode sheet, the separator, and the negative electrode sheet in sequence to form a cell; placing the cell in a battery casing, injecting electrolyte, and then sealing the battery casing to produce the battery. The cell can be wound or laminated.

[0054] The separator can be any separator material used in batteries. For example, the separator may include, but is not limited to, single-layer PP (polypropylene) film, single-layer PE (polyethylene) film, double-layer PP / PE, double-layer PP / PP, triple-layer PP / PE / PP, and other polymer separators, or non-woven fabrics. The electrolyte includes an electrolyte salt and an organic solvent. The specific types and compositions of the electrolyte salt and organic solvent are conventional in the battery field and can be selected according to actual needs.

[0055] The embodiments of the present disclosure also provide a device, which includes the above-mentioned lithium battery of the embodiments of the present disclosure. The above-mentioned device can be an electric vehicle (such as a car, motorcycle, bicycle, etc.), an electric toy, a 3C product (such as a mobile phone, a laptop, a tablet computer, a pen-input computer, an e-book player, a wearable device, etc.) and other electrical equipment; it can also be an energy storage system, etc. The energy storage system can include multiple lithium batteries and a battery management system. The energy storage system can also supply power to electrical equipment. Among them, the electrical equipment powered by the above-mentioned lithium battery has a long operating time and a fast charging speed.

[0056] The technical solution of the present disclosure is further described below in conjunction with a number of specific embodiments.

[0057] Example 1

[0058] A method for preparing a positive electrode sheet includes the following steps.

[0059] The first positive electrode lithium replenisher (for example, Li5FeO4 with a carbon coating layer on the surface, with the coating material accounting for 3wt%) is mixed with the positive electrode active material lithium iron phosphate (LFP), the binder PVDF, the conductive agent carbon black, the dispersant PVP, and the solvent NMP in a mass ratio of 100:50:4.5:4.5:2:240, and stirred evenly to obtain a primer slurry. The primer slurry is sprayed on the surface of the positive electrode current collector - aluminum foil, and then baked at a high temperature to volatilize the NMP to form an aluminum foil with a first lithium replenishing layer. Among them, the single-side density of the first lithium replenishing layer is 5.8g / m 2 , the thickness of single side is 4±1μm.

[0060] Lithium iron phosphate (LFP) was mixed with a binder PVDF, a carbon nanotube conductive agent, a graphene conductive agent, and a solvent NMP in a mass ratio of 100:2.5:1:0.5:60 to prepare a positive electrode slurry; the positive electrode slurry was applied on the first lithium supplement layer and baked to form a single-side surface density of 100g / m 2 , a positive electrode active material layer with a thickness of 40 μm on a single side.

[0061] Then, LFP was mixed evenly with binder PVDF, carbon nanotube conductive agent, graphene conductive agent, second positive electrode lithium supplement lithium oxalate (Li2C2O4), and solvent NMP in a mass ratio of 100:2.5:1:0.5:2:60 to prepare a mixed slurry, which was coated on the above-mentioned positive electrode active material layer and baked to form a single-side surface density of 100g / m 2 , a second lithium replenishing layer with a thickness of 40 μm on one side. If double-sided coating is required, repeat the above steps of forming the first lithium replenishing layer, the positive electrode active material layer, and the second lithium replenishing layer on the other side of the aluminum foil to obtain a double-sided positive electrode sheet.

[0062] Preparation of a lithium battery:

[0063] (1) Preparation of negative electrode sheet: The negative electrode active material graphite, binder SBR, thickener CMC, conductive agent carbon black and solvent H2O are mixed uniformly in a mass ratio of 100:2:2:1:120 to prepare a negative electrode slurry. The negative electrode slurry is applied to the negative electrode current collector - copper foil, and after baking, a single-side surface density of 100g / m 2 a negative electrode active material layer;

[0064] (2) Battery assembly: The positive electrode sheets, separators, and negative electrode sheets are stacked in sequence to obtain a battery cell; the stacked battery cell is then wound and placed in a battery casing. After assembly and baking, the prepared electrolyte is injected, and the battery casing is sealed with an air bag reserved to obtain a fully enclosed lithium battery for subsequent electrical performance testing.

[0065] Example 2

[0066] Preparation of a positive electrode sheet, which differs from Example 1 in that the second lithium replenishing layer includes two sub-layers with equal surface density, and the single-surface surface density of the second lithium replenishing layer is still the same as that of Example 1, which is 100g / m 2 , with a thickness of 40μm; among them, the formula of the lower layer slurry coated close to the positive electrode active material layer is LFP:PVDF:carbon nanotubes:graphene:Li2C2O4:NMP=100:2.6:1:0.5:1.0:60, and the formula of the upper layer slurry coated away from the positive electrode active material layer is LFP:PVDF:carbon nanotubes:graphene:Li2C2O4:NMP=100:2.4:1:0.5:3.0:60.

[0067] According to the method described in Example 1, the positive electrode sheets of Example 2 were assembled into a full-pack lithium battery.

[0068] Example 3

[0069] A positive electrode sheet is prepared, which differs from Example 1 mainly in that the first lithium replenishing layer does not contain the positive electrode active material LFP. Accordingly, the slurry formula for forming the first lithium replenishing layer is a mixture of Li5FeO4, binder PVDF, carbon black, dispersant PVP, and solvent NMP in a mass ratio of 100:4.5:4.5:2:240. The single-surface density of the first lithium replenishing layer is 4.0g / m 2 , the thickness of single side is 3±1μm.

[0070] According to the method described in Example 1, the positive electrode sheets of Example 3 were assembled into a full-pack lithium battery.

[0071] Example 4

[0072] A preparation method of a positive electrode sheet, which differs from Example 1 mainly in that the first positive electrode lithium replenishing agent in the first lithium replenishing layer is replaced by Li6CoO4 with a carbon coating layer on the surface (wherein the mass of the coating layer material accounts for 2.5wt%), and the positive electrode active material is replaced from LFP to lithium manganese iron phosphate (LMFP, with a structural formula of LiMn 0.6 Fe 0.4 PO4). The single surface density of the first lithium supplement layer is 5.0 g / m 2 , the thickness of single side is 4±1μm.

[0073] According to the method described in Example 1, the positive electrode sheets of Example 4 were assembled into a full-pack lithium battery.

[0074] Example 5

[0075] A preparation method for a positive electrode plate, which mainly differs from Example 2 in that: the first positive electrode lithium replenishing agent in the first lithium replenishing layer is replaced by Li6MnO4 with a carbon coating layer on the surface (wherein the mass proportion of the coating layer material is 3wt%); and the second positive electrode lithium replenishing agent in the second lithium replenishing layer is replaced by lithium nitride (Li3N).

[0076] Specifically, the formula of the primer slurry used to form the first lithium replenishing layer is the same as that in Example 1, except that the single-side density of the first lithium replenishing layer is 4.8 g / m 2 , the thickness of single side is 4±1μm.

[0077] The composition and surface density of the positive electrode active material layer are the same as those in Examples 1 and 3.

[0078] The second lithium replenishing layer includes two layers with equal surface density, and the single surface density of the second lithium replenishing layer is 64g / m 2 The thickness of a single side is 26 μm; among them, the formula of the lower layer slurry coated close to the positive electrode active material layer is LFP: PVDF: carbon nanotubes: graphene: Li3N: NMP = 100: 2.6: 1: 0.5: 0.6: 60, and the formula of the upper layer slurry coated away from the positive electrode active material layer is LFP: PVDF: carbon nanotubes: graphene: Li3N: NMP = 100: 2.4: 1: 0.5: 1.0: 60.

[0079] According to the method described in Example 1, the positive electrode sheets of Example 5 were assembled into a full-pack lithium battery.

[0080] Example 6

[0081] A preparation method of a positive electrode sheet, which is different from Example 1 mainly in that:

[0082] 1) The primer slurry for forming the first lithium replenishing layer is obtained by mixing the first positive electrode lithium replenishing agent (Li2NiO2 without a coating layer on the surface) with LFP, binder PVDF, conductive agent carbon black, dispersant PVP, and solvent NMP in a mass ratio of 100:30:4.5:4.5:2:240, wherein the single surface density of the first lithium replenishing layer is 8.4g / m 2 , coating thickness is 6±1μm;

[0083] 2) The second lithium replenishment layer includes two sublayers, the lower sublayer close to the positive electrode active material layer has a slurry formula of LFP: PVDF: carbon nanotubes: graphene: Li2CO3: NMP = 100: 2.6: 1: 0.5: 1: 60, and the upper sublayer away from the positive electrode active material layer has a slurry formula of LFP: PVDF: carbon nanotubes: graphene: Li2CO3: NMP = 100: 2.4: 1: 0.5: 2: 60. The ratio of the single surface density of the upper and lower second lithium replenishment sublayers is 6: 4, and the sum of the two is 100 g / m 2 In the second lithium replenishing layer of Example 6, the total mass of the second lithium replenishing agent Li2CO3 is 1.4% of the total mass of LFP.

[0084] According to the method described in Example 1, the positive electrode sheets of Example 6 were assembled into a full-pack lithium battery.

[0085] Example 7

[0086] A preparation method for a positive electrode plate, differing primarily from Example 6 in that the second lithium replenishing layer is a single layer. The mixed slurry used to form the second lithium replenishing layer is prepared by mixing LFP, a binder (PVDF), a carbon nanotube conductive agent, a graphene conductive agent, a second lithium replenishing agent (Li2CO3), and NMP in a mass ratio of 100:2.5:1:0.5:1.4:60. The single-surface density and thickness of the second lithium replenishing layer are the same as those in Example 6.

[0087] According to the method described in Example 1, the positive electrode sheets of Example 7 were assembled into a full-pack lithium battery.

[0088] Example 8

[0089] A positive electrode plate, which differs from Example 1 in that the first positive electrode lithium replenisher used is Li5FeO4 without a conductive coating layer on the surface.

[0090] Example 9

[0091] A method for preparing a positive electrode sheet includes:

[0092] The first positive electrode lithium supplement (specifically Li5FeO4 with a carbon coating layer on the surface, the coating material accounts for 3wt%) and the positive electrode active material lithium iron phosphate (LFP), binder PVDF, conductive agent carbon black, dispersant PVP, solvent NMP are mixed in a mass ratio of 61:50:4.5:4.5:2:120 to form a primer slurry. The primer slurry is sprayed on the surface of the positive electrode current collector - aluminum foil, and after baking, a single-side surface density of 20g / m 2 , the first lithium replenishment layer has a single-sided thickness of 16±1μm.

[0093] The positive electrode slurry with the same formula as Example 1 was coated on the first lithium supplement layer, and after baking, a single surface density of 150g / m 2 , a positive electrode active material layer with a single-side thickness of 60μm.

[0094] Then, LFP was mixed evenly with the binder PVDF, carbon nanotube conductive agent, graphene conductive agent, second positive electrode lithium supplement lithium oxalate (Li2C2O4), and solvent NMP in a mass ratio of 100:2.5:1:0.5:1:60 to prepare a mixed slurry, which was coated on the above-mentioned positive electrode active material layer and baked to form a single-side surface density of 30g / m 2 , a second lithium replenishing layer with a single-side thickness of 12 μm. Wherein, the single-side density of the first lithium replenishing layer is 10% of the sum of the single-side densities of the first lithium replenishing layer, the positive electrode active material layer, and the second lithium replenishing layer.

[0095] Repeat the above operations of forming the first lithium replenishing layer, the positive electrode active material layer, and the second lithium replenishing layer on the other side of the aluminum foil to obtain a double-sided positive electrode sheet.

[0096] According to the method described in Example 1, the positive electrode sheets of Example 9 were assembled into a fully encapsulated lithium battery.

[0097] Example 10

[0098] A method for preparing a positive electrode sheet, comprising:

[0099] The first positive electrode lithium supplement (specifically Li5FeO4 with a carbon coating layer on the surface, the coating material accounts for 3wt%) and the positive electrode active material lithium iron phosphate (LFP), binder PVDF, conductive agent carbon black, dispersant PVP, solvent NMP are mixed in a mass ratio of 61:50:4.5:4.5:2:120 to form a primer slurry, which is sprayed on the surface of the positive electrode current collector - aluminum foil, and is baked to form a surface density of 50g / m 2 , a first lithium replenishing layer with a thickness of 40±1 μm.

[0100] The positive electrode slurry with the same formula as Example 1 was coated on the first lithium supplement layer, and after baking, a single surface density of 375g / m 2 , a positive electrode active material layer with a single-side thickness of 150 μm.

[0101] Then, LFP was mixed evenly with binder PVDF, carbon nanotube conductive agent, graphene conductive agent, second positive electrode lithium supplement lithium oxalate (Li2C2O4), and solvent NMP in a mass ratio of 100:2.5:1:0.5:1:60 to prepare a mixed slurry, which was coated on the above-mentioned positive electrode active material layer and baked to form a single-side surface density of 75g / m 2, a second lithium replenishing layer with a single-sided thickness of 30μm.

[0102] Repeat the above operations of forming the first lithium replenishing layer, the positive electrode active material layer, and the second lithium replenishing layer on the other side of the aluminum foil to obtain a double-sided positive electrode sheet.

[0103] Example 11

[0104] A positive electrode sheet, the main difference from Example 1 is that: the single-surface density of the first lithium replenishing layer is 0.2 of the sum of the single-surface densities of the first lithium replenishing layer, the positive electrode active material layer, and the second lithium replenishing layer; the single-surface density of the second lithium replenishing layer is 0.1 times the sum of the single-surface densities of the first lithium replenishing layer, the positive electrode active material layer, and the second lithium replenishing layer.

[0105] The method for preparing the positive electrode sheet comprises:

[0106] The first positive electrode lithium replenisher (specifically Li5FeO4 with a carbon coating layer on the surface, the coating material accounts for 3wt%) and the positive electrode active material lithium iron phosphate (LFP), binder PVDF, conductive agent carbon black, dispersant PVP, solvent NMP are mixed in a mass ratio of 61:50:4.5:4.5:2:100 to form a primer slurry sprayed on the surface of the positive electrode current collector - aluminum foil, and after baking, the first lithium replenishing layer is formed. Among them, the single-side density of the first lithium replenishing layer is 40.0g / m 2 , the thickness of single side is 16μm.

[0107] The positive electrode slurry with the same formula as Example 1 was coated on the first lithium supplement layer, and after baking, a single surface density of 140 g / m 2 , the positive electrode active material layer has a single-side thickness of 56μm.

[0108] Then the mixed slurry with the same formula as Example 1 was coated on the above-mentioned positive electrode active material layer, and after baking, a single-side surface density of 20g / m 2 , a second lithium replenishing layer with a single-sided thickness of 8μm.

[0109] According to the method described in Example 1, the positive electrode sheets of Example 11 were assembled into a fully encapsulated lithium battery.

[0110] Example 12

[0111] A positive electrode sheet, which differs from Example 1 in that the single-surface density of the first lithium supplement layer is 0.5 g / m 2 The thickness of the single surface is 2±1μm; the single surface density of the positive electrode active material layer is 30g / m 2 , the thickness of the single surface is 12μm; the single surface density of the second lithium supplement layer is 150g / m 2The thickness per side is 60 μm. In the slurry used to form the second lithium replenishing layer, the mass of the second lithium replenishing agent, lithium oxalate, is 4% of the mass of the LFP. The single-side density of the first lithium replenishing layer is 0.003 of the sum of the single-side densities of the first lithium replenishing layer, the positive electrode active material layer, and the second lithium replenishing layer.

[0112] The preparation method of the positive electrode plate comprises: spraying the primer slurry with the same formula as Example 1 on the surface of the positive electrode current collector - aluminum foil, and baking it to form a first lithium replenishing layer. The single surface density of the first lithium replenishing layer is 0.5g / m 2 , the thickness of one side is 1μm.

[0113] The positive electrode slurry with the same formula as Example 1 was coated on the first lithium supplement layer, and after baking, a single surface density of 30 g / m 2 , a positive electrode active material layer with a single-side thickness of 12μm.

[0114] Then, LFP was mixed evenly with binder PVDF, carbon nanotube conductive agent, graphene conductive agent, second positive electrode lithium supplement lithium oxalate (Li2C2O4), and solvent NMP in a mass ratio of 100:2.5:1:0.5:3.7:60 to prepare a mixed slurry, which was coated on the above-mentioned positive electrode active material layer and baked to form a single-side surface density of 170g / m 2 , a second lithium replenishing layer with a single-side thickness of 68μm.

[0115] According to the method described in Example 1, the positive electrode sheets of Example 12 were assembled into a fully encapsulated lithium battery.

[0116] Example 13

[0117] A positive electrode sheet, the main difference from Example 1 is that the single-surface density of the first lithium supplement layer is 2.0g / m 2 The thickness of the single surface is 1 μm; the single surface density of the positive electrode active material layer is 18 g / m 2 , the thickness of the single surface is 8μm; the single surface density of the second lithium supplement layer is 180g / m 2 The thickness per side is 72 μm. In the slurry used to form the second lithium replenishment layer, the mass of lithium oxalate, the second lithium replenishment agent, is 1.1% of the mass of LFP. The single-side areal density of the first lithium replenishment layer is 0.01 of the sum of the single-side densities of the first lithium replenishment layer, the positive electrode active material layer, and the second lithium replenishment layer. The single-side areal density of the second lithium replenishment layer is 0.9 times the sum of the single-side densities of the first lithium replenishment layer, the positive electrode active material layer, and the second lithium replenishment layer.

[0118] The method for preparing the positive electrode sheet comprises:

[0119] The primer slurry with the same formula as Example 1 was sprayed on the surface of the positive electrode current collector - aluminum foil, and after baking, the aluminum foil with the first lithium supplement layer was formed. The single surface density of the first lithium supplement layer was 2.0 g / m 2 , the thickness of one side is 1μm.

[0120] The positive electrode slurry with the same formula as Example 1 was coated on the first lithium supplement layer, and after baking, a single surface density of 18g / m 2 , a positive electrode active material layer with a thickness of 8 μm on a single side.

[0121] Then, LFP was mixed evenly with binder PVDF, carbon nanotube conductive agent, graphene conductive agent, second positive electrode lithium supplement lithium oxalate (Li2C2O4), and solvent NMP in a mass ratio of 100:2.5:1:0.5:2.8:60 to prepare a mixed slurry, which was coated on the above-mentioned positive electrode active material layer and baked to form a single-side surface density of 180g / m 2 , a second lithium replenishing layer with a single-sided thickness of 72μm.

[0122] According to the method described in Example 1, the positive electrode sheets of Example 13 were assembled into a fully encapsulated lithium battery.

[0123] Example 14

[0124] A positive electrode sheet, the main difference from Example 1 is that the single-side density of the positive electrode active material layer is 66g / m 2 The thickness of the single surface is 26 μm, and the single surface density of the second lithium supplement layer is 132 g / m 2 The thickness per surface is 52 μm; the ratio of the single-surface density of the positive electrode active material layer to the second lithium replenishing layer is 0.5. In addition, the mass of lithium oxalate in the slurry used to form the second lithium replenishing layer is 1.5% of the mass of LFP.

[0125] The preparation method of the positive electrode plate comprises: spraying a primer slurry formed by mixing a first positive electrode lithium supplement agent (specifically Li5FeO4 with a carbon coating layer on the surface, the coating layer material accounts for 3wt%) with a positive electrode active material lithium iron phosphate (LFP), a binder PVDF, a conductive agent carbon black, a dispersant PVP, and a solvent NMP in a mass ratio of 100:50:4.5:4.5:2:100 on the surface of the positive electrode current collector - aluminum foil, and baking it to form a surface density of 5.8g / m 2 , the first lithium replenishment layer has a thickness of 4 μm.

[0126] The positive electrode slurry with the same formula as Example 1 was coated on the first lithium supplement layer, and after baking, a single surface density of 66g / m 2 , the positive electrode active material layer has a single-side thickness of 26μm.

[0127] Then, LFP was mixed evenly with binder PVDF, carbon nanotube conductive agent, graphene conductive agent, second positive electrode lithium supplement lithium oxalate (Li2C2O4), and solvent NMP in a mass ratio of 100:2.5:1:0.5:1.5:60 to prepare a mixed slurry, which was coated on the above-mentioned positive electrode active material layer and baked to form a single-side surface density of 132g / m 2 , a second lithium replenishing layer with a single-side thickness of 52μm.

[0128] According to the method described in Example 1, the positive electrode sheets of Example 14 were assembled into a full-pack lithium battery.

[0129] Example 15

[0130] A positive electrode sheet, the main difference from Example 1 is that the ratio of the single-surface density of the positive electrode active material layer to the second lithium supplement layer is 2.0, wherein the single-surface density of the positive electrode active material layer is 132g / m 2 The thickness of the single surface is 52 μm; the single surface density of the second lithium supplement layer is 66 g / m 2 , the thickness of a single side is 26 μm; in the slurry used to form the second lithium replenishing layer, the mass of lithium oxalate is 3% of the mass of LFP.

[0131] The preparation method of the positive electrode plate includes: spraying the primer slurry formed by mixing the first positive electrode lithium replenisher (specifically Li5FeO4 with a carbon coating layer on the surface, the coating material accounts for 3wt%) with the positive electrode active material lithium iron phosphate (LFP), the binder PVDF, the conductive agent carbon black, the dispersant PVP, and the solvent NMP in a mass ratio of 100:50:4.5:4.5:2:100 on the surface of the positive electrode current collector - aluminum foil, and baking to form the first lithium replenishing layer. The single-side density of the first lithium replenishing layer is 5.8g / m 2 , the thickness of single side is 4μm.

[0132] The positive electrode slurry with the same formula as Example 1 was coated on the first lithium supplement layer, and after baking, a single surface density of 132 g / m 2 , the positive electrode active material layer has a single-side thickness of 52μm.

[0133] Then, LFP was mixed evenly with binder PVDF, carbon nanotube conductive agent, graphene conductive agent, second positive electrode lithium supplement lithium oxalate (Li2C2O4), and solvent NMP in a mass ratio of 100:2.5:1:0.5:3:60 to prepare a mixed slurry, which was coated on the above-mentioned positive electrode active material layer and baked to form a single-side surface density of 66g / m 2 , a second lithium replenishing layer with a single-sided thickness of 26μm.

[0134] According to the method described in Example 1, the positive electrode sheets of Example 15 were assembled into a fully encapsulated lithium battery.

[0135] Example 16

[0136] A positive electrode sheet, the main difference from Example 1 is that the single-side density of the positive electrode active material layer is 34g / m 2 The thickness of the single surface is 14 μm, and the single surface density of the second lithium supplement layer is 166 g / m 2 The thickness per side is 66 μm, and the mass of lithium oxalate in the slurry used to form the second lithium replenishing layer is 1.2% of the mass of LFP. The ratio of the single-side density of the positive electrode active material layer to the second lithium replenishing layer is 0.2.

[0137] The preparation method of the positive electrode plate includes:

[0138] The first positive electrode lithium replenisher (specifically Li5FeO4 with a carbon coating layer on the surface, with the coating material accounting for 3wt%) is mixed with the positive electrode active material lithium iron phosphate (LFP), the binder PVDF, the conductive agent carbon black, the dispersant PVP, and the solvent NMP in a mass ratio of 100:50:4.5:4.5:2:100 to form a primer slurry sprayed on the surface of the positive electrode current collector - aluminum foil. After baking, the first lithium replenisher layer is formed. The single-surface density of the first lithium replenisher layer is 5.8g / m 2 , the thickness of single side is 4μm.

[0139] The positive electrode slurry with the same formula as Example 1 was coated on the first lithium supplement layer, and after baking, a single surface density of 34g / m 2 , a positive electrode active material layer with a single-side thickness of 14μm.

[0140] Then, LFP was mixed evenly with binder PVDF, carbon nanotube conductive agent, graphene conductive agent, second positive electrode lithium supplement lithium oxalate (Li2C2O4), and solvent NMP in a mass ratio of 100:2.5:1:0.5:1.2:60 to prepare a mixed slurry, which was coated on the above-mentioned positive electrode active material layer and baked to form a single-side surface density of 166g / m 2 , a second lithium replenishing layer with a single-side thickness of 66μm.

[0141] According to the method described in Example 1, the positive electrode sheets of Example 16 were assembled into a fully encapsulated lithium battery.

[0142] Example 17

[0143] The main difference between Example 17 and Example 1 is that the single-surface density of the positive electrode active material layer is 20 g / m 2 , the thickness of the single surface is 8μm; the single surface density of the second lithium supplement layer is 180g / m2 , the thickness on one side is 72 μm; in the second lithium replenishing layer of the positive electrode plate of Example 17, the total mass of the second lithium replenishing agent is 1.1% of the total mass of LFP.

[0144] The preparation of the positive electrode sheet includes:

[0145] The first positive electrode lithium replenisher (specifically Li5FeO4 with a carbon coating layer on the surface, with the coating material accounting for 3wt%) is mixed with the positive electrode active material lithium iron phosphate (LFP), the binder PVDF, the conductive agent carbon black, the dispersant PVP, and the solvent NMP in a mass ratio of 100:50:4.5:4.5:2:100 to form a primer slurry that is sprayed on the surface of the positive electrode current collector - aluminum foil, and is baked to form the first lithium replenishing layer. Among them, the single-side density of the first lithium replenishing layer is 5.8g / m 2 , the thickness of one side is 4μm.

[0146] The positive electrode slurry with the same formula as Example 1 was coated on the first lithium supplement layer, and after baking, a single surface density of 20g / m 2 , a positive electrode active material layer with a thickness of 8 μm on a single side.

[0147] Then, LFP was mixed evenly with binder PVDF, carbon nanotube conductive agent, graphene conductive agent, second positive electrode lithium supplement lithium oxalate (Li2C2O4), and solvent NMP in a mass ratio of 100:2.5:1:0.5:1.1:60 to prepare a mixed slurry, which was coated on the above-mentioned positive electrode active material layer and baked to form a single-side surface density of 180g / m 2 , a second lithium replenishing layer with a single-sided thickness of 72μm.

[0148] According to the method described in Example 1, the positive electrode sheets of Example 17 were assembled into a fully encapsulated lithium battery.

[0149] Example 18

[0150] The main difference between Example 18 and Example 1 is that in the positive electrode sheet of Example 18, the single-side density of the positive electrode active material layer is 159 g / m 2 , the thickness of the single surface is 64μm; the single surface density of the second lithium supplement layer is 41g / m 2 The thickness on one side is 16 μm. In the second lithium replenishing layer, the total mass of the second lithium replenishing agent is 5% of the total mass of the LFP. The single-side density of the second lithium replenishing layer is 0.2 times the sum of the single-side densities of the first lithium replenishing layer, the positive electrode active material layer, and the second lithium replenishing layer.

[0151] The preparation of the positive electrode sheet includes:

[0152] The first positive electrode lithium replenisher (specifically Li5FeO4 with a carbon coating layer on the surface, with the coating material accounting for 3wt%) is mixed with the positive electrode active material lithium iron phosphate (LFP), the binder PVDF, the conductive agent carbon black, the dispersant PVP, and the solvent NMP in a mass ratio of 100:50:4.5:4.5:2:100 to form a primer slurry that is sprayed on the surface of the positive electrode current collector - aluminum foil, and is baked to form the first lithium replenishing layer. Among them, the single-side density of the first lithium replenishing layer is 5.8g / m 2 , the thickness of single side is 4μm.

[0153] The positive electrode slurry with the same formula as Example 1 was coated on the first lithium supplement layer, and after baking, a single surface density of 159 g / m 2 , the positive electrode active material layer has a single-side thickness of 64μm.

[0154] Then, LFP was mixed evenly with binder PVDF, carbon nanotube conductive agent, graphene conductive agent, second positive electrode lithium supplement lithium oxalate (Li2C2O4), and solvent NMP in a mass ratio of 100:2.5:1:0.5:5:60 to prepare a mixed slurry, which was coated on the above-mentioned positive electrode active material layer and baked to form a single-side surface density of 41g / m 2 , a second lithium replenishing layer with a single-sided thickness of 16μm.

[0155] According to the method described in Example 1, the positive electrode sheets of Example 18 were assembled into a fully encapsulated lithium battery.

[0156] Example 19

[0157] The main difference between Example 19 and Example 1 is that in the positive electrode sheet of Example 19, the single-side density of the positive electrode active material layer is 178 g / m 2 The thickness of the single surface is 71 μm; the single surface density of the second lithium supplement layer is 22 g / m 2 The thickness on one side is 9 μm. In the second lithium replenishing layer, the total mass of the second lithium replenishing agent is 10% of the total mass of the LFP. The single-side density of the second lithium replenishing layer is 0.11 times the sum of the single-side densities of the first lithium replenishing layer, the positive electrode active material layer, and the second lithium replenishing layer.

[0158] The preparation of the positive electrode sheet includes:

[0159] The first positive electrode lithium replenisher (specifically Li5FeO4 with a carbon coating layer on the surface, with the coating material accounting for 3wt%) is mixed with the positive electrode active material lithium iron phosphate (LFP), the binder PVDF, the conductive agent carbon black, the dispersant PVP, and the solvent NMP in a mass ratio of 100:50:4.5:4.5:2:100 to form a primer slurry that is sprayed on the surface of the positive electrode current collector - aluminum foil, and then baked to form the first lithium replenishing layer. The single-side density of the first lithium replenishing layer is 5.8g / m 2 , the thickness of single side is 4μm.

[0160] The positive electrode slurry with the same formula as Example 1 was coated on the first lithium supplement layer, and after baking, a single surface density of 178g / m 2 , the positive electrode active material layer has a single-side thickness of 71μm.

[0161] Then, LFP was mixed evenly with binder PVDF, carbon nanotube conductive agent, graphene conductive agent, second positive electrode lithium supplement lithium oxalate (Li2C2O4), and solvent NMP in a mass ratio of 100:2.5:1:0.5:10:60 to prepare a mixed slurry, which was coated on the above-mentioned positive electrode active material layer and baked to form a single-side surface density of 22g / m 2 , a second lithium replenishing layer with a single-sided thickness of 9μm.

[0162] According to the method described in Example 1, the positive electrode sheets of Example 19 were assembled into a fully encapsulated lithium battery.

[0163] Example 20

[0164] The main difference between Example 20 and Example 1 is that in the positive electrode of Example 20, the total mass of the second lithium replenishing agent in the second lithium replenishing layer is 0.5% of the total mass of LFP; the single surface density of the first lithium replenishing layer is 9.5g / m 2 , the thickness of single side is 7μm.

[0165] The preparation of the positive electrode sheet includes:

[0166] The first positive electrode lithium replenishing agent (specifically Li5FeO4 with a carbon coating layer on the surface, the coating material accounts for 3wt%) and the positive electrode active material lithium iron phosphate (LFP), binder PVDF, conductive agent carbon black, dispersant PVP, solvent NMP in a mass ratio of 100:50:4.5:4.5:2:100 to form a primer slurry sprayed on the surface of the positive electrode current collector - aluminum foil, and after baking, the first lithium replenishing layer is formed. The single-side density of the first lithium replenishing layer is 9.5g / m 2 , the thickness of single side is 7μm.

[0167] The positive electrode slurry with the same formula as Example 1 was coated on the first lithium supplement layer, and after baking, a single-side surface density of 100 g / m 2 , a positive electrode active material layer with a thickness of 40 μm on a single side.

[0168] Then, LFP was mixed evenly with binder PVDF, carbon nanotube conductive agent, graphene conductive agent, second positive electrode lithium supplement lithium oxalate (Li2C2O4), and solvent NMP in a mass ratio of 100:2.5:1:0.5:0.5:60 to prepare a mixed slurry, which was coated on the above-mentioned positive electrode active material layer and baked to form a single-side surface density of 100g / m 2 , a second lithium replenishing layer with a single-sided thickness of 40μm.

[0169] According to the method described in Example 1, the positive electrode sheets of Example 20 were assembled into a full-pack lithium battery.

[0170] Example 21

[0171] The main difference between Example 21 and Example 1 is that in the positive electrode sheet of Example 21, the total mass of the second lithium replenishing agent in the second lithium replenishing layer is 0.2% of the total mass of the positive electrode active material; the single surface density of the first lithium replenishing layer is 10.0 g / m 2 , with a thickness of 8μm.

[0172] The preparation of the positive electrode sheet includes:

[0173] The first positive electrode lithium replenishing agent (specifically Li5FeO4 with a carbon coating layer on the surface, the coating material accounts for 3wt%) and the positive electrode active material lithium iron phosphate (LFP), binder PVDF, conductive agent carbon black, dispersant PVP, solvent NMP in a mass ratio of 100:50:4.5:4.5:2:100 to form a primer slurry sprayed on the surface of the positive electrode current collector - aluminum foil, and after baking, the first lithium replenishing layer is formed. The single surface density of the first lithium replenishing layer is 10.0g / m 2 , with a thickness of 8μm.

[0174] The positive electrode slurry with the same formula as Example 1 was coated on the first lithium supplement layer, and after baking, a single-side surface density of 100 g / m 2 , a positive electrode active material layer with a thickness of 40 μm on a single side.

[0175] Then, LFP was mixed evenly with binder PVDF, carbon nanotube conductive agent, graphene conductive agent, second positive electrode lithium supplement lithium oxalate (Li2C2O4), and solvent NMP in a mass ratio of 100:2.5:1:0.5:0.2:60 to prepare a mixed slurry, which was coated on the above-mentioned positive electrode active material layer and baked to form a single-side surface density of 100g / m 2, a second lithium replenishing layer with a single-sided thickness of 40μm.

[0176] According to the method described in Example 1, the positive electrode sheets of Example 21 were assembled into a full-pack lithium battery.

[0177] In order to highlight the beneficial effects of the present disclosure, the present disclosure also provides the following comparative examples 1-4.

[0178] Comparative Example 1

[0179] A non-lithium supplemented positive electrode sheet is prepared by uniformly mixing lithium iron phosphate (LFP), a binder (PVDF), carbon nanotubes (CNTs), graphene, and a solvent (NMP) in a mass ratio of 100:2.5:1:0.5:60 to prepare a positive electrode slurry. The positive electrode slurry is coated on an aluminum foil current collector and dried to form a single-sided surface density of 200 g / m 2 The positive electrode coating is then applied to the other side of the aluminum foil and dried to obtain a double-sided positive electrode sheet.

[0180] According to the method described in Example 1, the positive electrode sheets of Comparative Example 1 were assembled into a fully encapsulated lithium battery.

[0181] Comparative Example 2

[0182] A positive electrode plate, which differs from Example 1 in that only a mixed layer containing both LFP and a first positive electrode lithium replenisher is provided on the aluminum foil.

[0183] The preparation of the positive electrode plate includes: mixing LFP, binder PVDF, carbon nanotube conductive agent, graphene conductive agent, first positive electrode lithium supplement agent (same as Example 1, Li5FeO4 with a conductive carbon coating layer on the surface), and solvent NMP in a mass ratio of 100:2.5:1:0.5:2:60 to prepare a mixed slurry. The mixed slurry is coated on an aluminum foil current collector and dried to form a single-side surface density of 200g / m 2 positive electrode coating.

[0184] According to the method described in Example 1, the positive electrode sheets of Comparative Example 2 were assembled into a fully enclosed lithium battery.

[0185] Comparative Example 3

[0186] A positive electrode plate, which differs from Example 1 in that only a mixed layer containing LFP and a second positive electrode lithium replenisher is provided on the aluminum foil.

[0187] The preparation of the positive electrode sheet includes: mixing LFP, binder PVDF, carbon nanotubes, graphene, second positive electrode lithium supplement Li2C2O4, and solvent NMP in a mass ratio of 100:2.5:1:0.5:2:60 to prepare a positive electrode slurry; coating the positive electrode slurry on an aluminum foil current collector, and drying it to form a single-side surface density of 200g / m 2 positive electrode mixed layer.

[0188] According to the method described in Example 1, the positive electrode sheets of Comparative Example 3 were assembled into a fully enclosed lithium battery.

[0189] Comparative Example 4

[0190] A positive electrode plate, which differs from Example 1 mainly in that a mixed layer containing a first positive electrode lithium replenisher, a second positive electrode lithium replenisher and a positive electrode active material is directly provided on the aluminum foil.

[0191] LFP, binder PVDF, carbon nanotubes, graphene, the first positive electrode lithium replenisher, the second positive electrode lithium replenisher Li2C2O4, and solvent NMP are uniformly mixed in a mass ratio of 100:2.5:1:0.5:1:1:60 to obtain a positive electrode slurry; the positive electrode slurry is directly coated on aluminum foil, and after baking, a single-sided surface density of 200 g / m is formed. 2 The positive electrode coating is then applied to the other side of the aluminum foil and baked to obtain a double-sided positive electrode sheet.

[0192] According to the method described in Example 1, the positive electrode sheets of Comparative Example 4 were assembled into a fully enclosed sodium battery.

[0193] Comparative Example 5

[0194] A positive electrode sheet differs from Example 1 in that: there is no second lithium replenishing layer on the positive electrode active material layer, and the single-surface density of the positive electrode active material layer is equal to the sum of the single-surface density of the positive electrode active material layer and the second lithium replenishing layer in Example 1.

[0195] The preparation of the positive electrode plate includes: (1) mixing the first positive electrode lithium replenisher (specifically Li5FeO4 with a carbon coating layer on the surface, the coating material accounts for 3wt%) with the positive electrode active material lithium iron phosphate (LFP), binder PVDF, conductive agent carbon black, dispersant PVP, and solvent NMP in a mass ratio of 100:50:4.5:4.5:2:240, stirring evenly to obtain a primer slurry, spraying the primer slurry on the surface of the positive electrode current collector - aluminum foil, and then baking at a high temperature to volatilize the NMP to form an aluminum foil with a first lithium replenishing layer. The single-sided surface density of the first lithium replenishing layer is 11.6g / m 2, the thickness of a single surface is 8±1μm; (2) LFP, binder PVDF, carbon nanotube conductive agent, graphene conductive agent, and solvent NMP are mixed uniformly in a mass ratio of 100:2.5:1:0.5:60 to prepare a positive electrode slurry; the positive electrode slurry is coated on the above-mentioned first lithium supplement layer, and after drying, a single surface density of 200g / m 2 positive electrode active material layer.

[0196] According to the method described in Example 1, the positive electrode sheets of Comparative Example 5 were assembled into a fully encapsulated lithium battery.

[0197] Comparative Example 6

[0198] The main difference between a positive electrode sheet and Example 1 is that the positions of the second lithium replenishing layer and the first lithium replenishing layer in Example 1 are reversed, and there is no separate positive electrode active material layer.

[0199] The preparation method of the positive electrode plate includes:

[0200] LFP, binder PVDF, carbon nanotubes, graphene, second positive electrode lithium supplement Li2C2O4, and solvent NMP were mixed uniformly in a mass ratio of 100:2.5:1:0.5:2:60 to prepare a first positive electrode slurry; the first positive electrode slurry was coated on an aluminum foil current collector and dried to form a single-side surface density of 200g / m 2 The first material layer.

[0201] The first positive electrode lithium supplement agent (same as in Example 1) was mixed with LFP, binder PVDF, conductive agent carbon black, dispersant PVP, and solvent NMP in a mass ratio of 100:50:4.5:4.5:2:240 to prepare a second slurry; the second slurry was coated on the first material layer, and after drying, a single-side surface density of 5.8 g / m was formed. 2 The second material layer.

[0202] Comparative Example 7

[0203] A positive electrode is prepared, which is different from Comparative Example 1 in that the positive electrode active material is replaced by lithium iron phosphate with lithium manganese iron phosphate.

[0204] The preparation method of the positive electrode comprises: mixing lithium manganese iron phosphate, binder PVDF, carbon nanotube conductive agent, graphene conductive agent, and solvent NMP in a mass ratio of 100:2.5:1:0.5:60 to prepare a positive electrode slurry. The positive electrode slurry is coated on an aluminum foil current collector and dried to form a single-side surface density of 200g / m 2 Repeat the above steps of forming the positive electrode material layer on the other side of the aluminum foil, and then roll-press to obtain the positive electrode.

[0205] According to the method described in Example 1, the positive electrode of Comparative Example 7 was assembled into a full-pack lithium battery.

[0206] In order to strongly support the beneficial effects brought about by the technical solution of the present disclosure, the full-pack lithium batteries of the above embodiments or comparative examples were subjected to the following performance tests:

[0207] a. Positive Electrode Gram Capacity Test: At room temperature (25±3°C), charge each battery at a constant current and constant voltage of 1 / 3C to an upper voltage limit of 4.6V (C represents the battery capacity) for formation. Record the initial charge capacity (i.e., the charge capacity at formation). After aging (aging procedure: 100% SOC at 45°C for 48 hours), discharge each battery at 1 / 3C to a lower voltage limit of 2.0V. Calculate the initial discharge capacity and average discharge voltage. Here, the positive electrode gram capacity = initial discharge capacity / total mass of the positive electrode active material; the battery's mass energy density = initial discharge capacity × average discharge voltage / battery mass.

[0208] b. Cycling Performance Test: At room temperature (25±3°C), charge each aged battery at a constant current and constant voltage rate of 1 / 3C to an upper voltage limit of 3.8V. Then, discharge at a constant current and constant voltage rate of 1 / 3C to a lower voltage limit of 2.0V. Repeat this charge and discharge process 500 times, and record the capacity retention rate after 500 cycles. Capacity retention rate after 500 cycles = discharge capacity at the 500th cycle / discharge capacity at the first discharge after aging.

[0209] c. Battery Direct Current Internal Resistance (DCIR) Test: At room temperature (25±3°C), each aged battery was charged at a constant current of 1 / 3C to an upper voltage limit of 3.8V. The battery was then discharged at a constant current of 1 / 3C to a lower voltage limit of 2.0V. After three cycles, the battery was again charged at a constant current of 1 / 3C at 25°C to 50% SOC. The battery voltage after standing for one hour was recorded as V1. The battery was then discharged at 1.5C for 30 seconds, and the battery voltage at the end of discharge was recorded as V2. DCIR = (V1 - V2) / 1.5C.

[0210] d. Utilization rate test of lithium supplement materials:

[0211] Non-lithium-supplemented batteries corresponding to the lithium-supplemented batteries of the embodiments and comparative examples of the present disclosure were prepared (wherein, embodiments 1-21 and comparative examples 2-6 are all lithium-supplemented batteries, and comparative examples 1 and 7 are non-lithium-supplemented batteries). The manufacturing processes of the non-lithium-supplemented batteries and the corresponding lithium-supplemented batteries are basically the same, except that no lithium-supplementing agent is added to the positive electrode of the non-lithium-supplemented batteries.

[0212] Then, at room temperature (25±3°C), each of the above batteries was charged at a constant current and constant voltage rate of 1 / 3C to an upper limit voltage of 4.6V for formation. After aging, it was discharged at a constant current and constant voltage rate of 1 / 3C to a lower limit voltage of 2.0V. The discharge capacity of each lithium-supplemented battery was recorded as C1, and the discharge capacity of the non-lithium-supplemented battery corresponding to each lithium-supplemented battery was recorded as C2. The utilization rate of the lithium-supplemented material = (C1-C2) / (mass of the lithium-supplemented material × theoretical gram capacity of the lithium-supplemented material).

[0213] The relevant test results are summarized in Table 1 below.

[0214] Table 1

[0215] From the comparison of Example 1 and Comparative Examples 1-5 in Table 1, it can be seen that when the positive electrode of the battery does not contain a lithium replenishing material (Comparative Example 1), the positive electrode capacity and mass energy density of the battery are both low, and the DCIR value is high. However, when the positive electrode contains only one type of positive electrode lithium replenishing agent (such as Comparative Examples 2, 3, and 5), or the positive electrode contains two types of positive electrode lithium replenishing agents but they are not distributed as in Comparative Examples 4 and 6 of Example 1 of the present disclosure, although the positive electrode capacity and volume energy density of the battery are improved compared to Comparative Example 1, the DCIR value impedance of the battery is still high (which can reflect the poor power performance of the battery), and the utilization rate of the lithium replenishing material is not high. When the positive electrode active materials are the same, Example 1 of the present disclosure introduces the above-mentioned first positive electrode lithium replenishing agent and the second positive electrode lithium replenishing agent into the positive electrode of the lithium battery at the same time, and arranges them in the manner required by the present disclosure, the positive electrode capacity, the utilization rate of the lithium replenishing material are high, and the mass energy density of the battery is high, the impedance is low, the average discharge voltage is increased, the high-power discharge capability and continuous discharge capability of the battery are improved, the cycle capacity retention rate is also improved, and the battery life can be improved. The only difference from Example 1 is that Example 2, which has two second lithium replenishing layers, also has similar effects, and the effects are even better than those of Example 1. In addition, a comparison between Comparative Example 7 and Example 4 also reveals similar phenomena as those between Example 1 and Comparative Example 1.

[0216] The above-described embodiments merely represent several implementation methods of the present disclosure. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the scope of the present disclosure, all of which fall within the scope of protection of the present disclosure. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A positive electrode sheet (100), characterized in that: The invention comprises a positive electrode current collector (10) and a coating structure (20) arranged on at least one side of the positive electrode current collector (10), wherein the coating structure (20) comprises a first lithium replenishing layer (21), a positive electrode active material layer (22) and a second lithium replenishing layer (23) which are stacked in sequence, and the first lithium replenishing layer (21) is close to the positive electrode current collector (10); wherein the first lithium replenishing layer (21) comprises a first positive electrode lithium replenishing agent (210), the positive electrode active material layer (22) comprises a first positive electrode active material (221), and the second lithium replenishing layer (23) comprises a second positive electrode lithium replenishing agent (230) and a second positive electrode active material (231), wherein the first coulombic efficiency of the first positive electrode lithium replenishing agent (210) is less than 30%, and the second positive electrode lithium replenishing agent (230) can be decomposed to release lithium ions and generate gas.

2. The positive electrode sheet (100) according to claim 1, characterized in that: The first positive electrode lithium replenisher (210) is selected from one or more of Li6CoO4, Li2MoO3, Li5FeO4, Li6MnO4, Li2NiO2, Li2CuO2, Li3PO4, Li4SiO4, Li2SiO3, Li3VO4, Li2VO3, Li5ReO6, Li2RuO3, Li2MnO3, Li2MoO3, Li2S, and LiF; the second positive electrode lithium replenisher (230) is selected from one or more of Li2CO3, Li3N, Li2O2, Li2O, Li2C2O4, Li2C4O4, Li2C3O5, and Li2C4O6.

3. The positive electrode sheet (100) according to claim 1, characterized in that: The ratio of the single-surface surface density of the first lithium replenishing layer (21) to the single-surface surface density of the coating structure (20) is 0.01-0.2; the ratio of the single-surface surface density of the positive electrode active material layer (22) to the single-surface surface density of the coating structure (20) is 0.1-0.9; and the ratio of the single-surface surface density of the second lithium replenishing layer (23) to the single-surface surface density of the coating structure (20) is 0.1-0.

9.

4. The positive electrode sheet (100) according to any one of claims 1 to 3, characterized in that: The single-surface surface density of the positive electrode active material layer (22) and / or the second lithium replenishing layer (23) is greater than the single-surface surface density of the first lithium replenishing layer (21).

5. The positive electrode sheet (100) according to any one of claims 1 to 4, characterized in that: The single-surface density of the first lithium supplement layer (21) is 0.5-20 g / m 2 The single-surface density of the positive electrode active material layer (22) and the second lithium supplement layer (23) is 50-500 g / m 2 within the range.

6. The positive electrode sheet (100) according to any one of claims 1 to 5, characterized in that: The ratio of the single-surface density of the positive electrode active material layer (22) to the second lithium supplement layer (23) is in the range of 0.5-2.

0.

7. The positive electrode sheet (100) according to any one of claims 1 to 6, characterized in that: The single-side thickness of the first lithium replenishing layer (21) is 1-20 μm.

8. The positive electrode sheet (100) according to any one of claims 1 to 7, characterized in that: The single-side thickness of the positive electrode active material layer (22) or the second lithium supplement layer (23) is 20-200 μm.

9. The positive electrode sheet (100) according to any one of claims 1 to 8, characterized in that: The first lithium replenishing layer (21) includes a third positive electrode active material whose mass percentage content does not exceed that of the first positive electrode lithium replenishing agent (210).

10. The positive electrode sheet (100) according to any one of claims 1 to 9, characterized in that: The first lithium replenishing layer (21) comprises the following components in percentage by mass: 50%-90% of the first positive electrode lithium replenishing agent, 0-40% of the third positive electrode active material, 0.5-10% of the binder, and 0.5-10% of the conductive agent.

11. The positive electrode sheet (100) according to any one of claims 1 to 10, characterized in that: In the second lithium replenishing layer (23), the total mass of the second positive electrode lithium replenishing agent (230) is 0.5% to 5% of the total mass of the second positive electrode active material (231).

12. The positive electrode sheet (100) according to claim 11, characterized in that: In the second lithium replenishing layer (23), the total mass percentage of the second positive electrode active material (231) is greater than 80%.

13. The positive electrode sheet (100) according to claim 11, characterized in that: In the second lithium replenishing layer (23), the total mass percentage of the second positive electrode active material (231) is greater than 90%.

14. The positive electrode sheet (100) according to any one of claims 1 to 13, characterized in that: The second lithium replenishing layer (23) comprises n second lithium replenishing sublayers, where n≥2, wherein the mass ratio of the second positive electrode lithium replenishing agent to the second positive electrode active material in each second lithium replenishing sublayer tends to increase from the positive electrode current collector (10) to the first lithium replenishing layer (21).

15. The positive electrode sheet (100) according to any one of claims 1 to 14, characterized in that: The second lithium replenishing layer comprises n second lithium replenishing sublayers, where n≥2, wherein the mass ratio of the second positive electrode lithium replenishing agent to the second positive electrode active material in each second lithium replenishing sublayer increases layer by layer from the positive electrode current collector (10) to the first lithium replenishing layer (21).

16. The positive electrode sheet (100) according to claim 14 or 15, characterized in that: Among the n layers of the second lithium supplementation sub-layers, at least two adjacent layers satisfy: A m / (D m / D m-1 )-A m-1 ≥5%; Among them, A m-1 is the mass ratio of the second positive electrode lithium replenisher in the m-1th second lithium replenisher sublayer to the total second positive electrode lithium replenisher in the second lithium replenisher layer (23), A m is the mass ratio of the second positive electrode lithium replenishing agent in the mth second lithium replenishing sublayer to the total second positive electrode lithium replenishing agent in the second lithium replenishing layer, D m-1 is the thickness of the second lithium supplementation sublayer of the m-1th layer, D m is the thickness of the mth second lithium-replenishing sublayer, m is any integer between 2 and n; on the same side of the positive electrode current collector (10), the m-1th second lithium-replenishing sublayer is closer to the positive electrode current collector (10) than the mth second lithium-replenishing sublayer.

17. The positive electrode sheet (100) according to any one of claims 1 to 16, characterized in that: The content of the lithium supplement in the positive electrode active material layer (22) is less than or equal to 1%.

18. A lithium battery, characterized in that: Comprising the positive electrode sheet as described in any one of claims 1-17.

19. The lithium battery according to claim 18, characterized in that: It includes a negative electrode plate, and a separator and an electrolyte arranged between the negative electrode plate and the positive electrode plate.

20. A device, characterized in that: Comprising the lithium battery as described in claim 18 or 19, wherein the device is an electrical equipment or an energy storage system.

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