Positive pole piece, lithium battery and device

Abstract

The invention provides a positive pole piece, a lithium battery and a device. The positive pole piece comprises a positive current collector as well as a bottom coating and a positive coating which are sequentially stacked on at least one side of the positive current collector, the bottom coating contains a first positive lithium supplement agent, the positive coating contains a positive active material and a second positive lithium supplement agent, the first coulombic efficiency of the first positive lithium supplement agent is less than 30%, and the second coulombic efficiency of the second positive lithium supplement agent is less than 30%. And the second positive electrode lithium supplement agent can be decomposed to generate gas at a voltage greater than the lithium removal potential thereof. The first positive electrode lithium supplement agent and the second positive electrode lithium supplement agent are simultaneously introduced into the positive electrode plate and are arranged in a layered manner, so that many problems caused by independent use of the first positive electrode lithium supplement agent and the second positive electrode lithium supplement agent can be reduced, the lithium supplement utilization rates of the positive electrode plate and the second positive electrode lithium supplement agent are improved, the battery impedance is not obviously increased, and the battery power performance is improved.

Description

Technical Field

[0001] The present application 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

[0002] During the first charge of a lithium battery, a solid electrolyte film (SEI film for short) will form on the surface of the negative electrode, which will consume the active lithium ions released from the positive electrode, reducing 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 taken measures to pre-add lithium replenishers that can provide active lithium ions to lithium batteries. 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 plate to achieve pre-lithiation, positive electrode lithium replenishment is safer and more compatible with existing battery preparation processes.

[0003] Among them, positive electrode lithium replenishment technology is to introduce positive electrode lithium replenishers with high reversible lithium removal into the positive electrode of the battery. Positive electrode lithium replenishers are mainly divided into two categories. The first category is lithium-rich materials with extremely low first coulomb efficiency. After removing lithium ions at a certain voltage, a part of the main structure or lithium removal products remains on the positive electrode side; the second category is sacrificial lithium replenishers that can decompose to produce lithium ions and gases at a certain voltage. However, there are certain problems with the separate use of these two types of positive electrode lithium replenishers in lithium batteries. For example, if all the positive electrode active materials are mixed with the first type of positive electrode lithium replenisher in a layer, the liquid phase diffusion impedance of the positive electrode will be significantly increased, reducing the power performance of the battery. For example, the positive electrode coating formed by the mixture of the second type of positive electrode lithium replenisher and the positive electrode active material is in direct contact with the positive electrode current collector. The gas generated by the decomposition of this type of lithium replenisher is difficult to be discharged smoothly, and the residual gas will reduce its utilization rate, increase the battery impedance, and reduce the battery power performance.

[0004] 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. Summary of the invention

[0005] In view of this, the present application introduces the above-mentioned lithium supplement material with low coulombic efficiency and the lithium supplement material that can decompose and produce gas into the positive electrode of the battery. By reasonably distributing the two materials, the negative effects of using a single 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.

[0006] Specifically, the first aspect of the present application 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 positive electrode lithium replenishing agent has a first coulombic efficiency of less than 30%, and the second positive electrode lithium replenishing agent can decompose to release lithium ions and generate gas.

[0007] In the above-mentioned positive electrode plate of the embodiment of the present application, 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 respectively containing the two, which can ensure the high structural stability of the overall coating structure, and can reduce the many problems caused by using these two positive electrode lithium replenishers alone, and their lithium replenishment utilization rates are improved, the energy density of the battery is effectively improved, and the battery impedance is low and the power performance is good.

[0008] In a second aspect, the present application provides a lithium battery, which includes the positive electrode plate as described in the first aspect of the present application.

[0009] 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 at the same time, the battery impedance is low and the power performance is good.

[0010] In a third aspect, the present application provides a device comprising the lithium battery described in the second aspect of the present application, and the device is an electrical device or an energy storage system. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1A and Figure 1B A schematic diagram of the structure of the positive electrode plate provided in this application.

[0012] Figure 2 Another structural schematic diagram of the positive electrode plate provided in this application. DETAILED DESCRIPTION

[0013] The technical solution of the embodiments of the present application will be described below in conjunction with the accompanying drawings.

[0014] Please also see Figure 1A and Figure 1BThe embodiment of the present application provides a positive electrode plate 100, including a positive electrode collector 10 and a coating structure 20 arranged on at least one side of the positive electrode collector 10, the coating structure 20 includes a first lithium replenishing layer 21, a positive electrode active material layer 22 and a second lithium replenishing layer 23 stacked in sequence, and the first lithium replenishing layer 21 is close to the positive electrode collector 10, wherein the first lithium replenishing layer 21 includes a first positive electrode lithium replenishing agent 210, the positive electrode active material layer 22 includes a first positive electrode active material 221, and the second lithium replenishing layer 23 includes a second positive electrode lithium replenishing agent 230 and a second positive electrode active material 231, wherein the first positive electrode lithium replenishing agent 210 has a first coulombic efficiency of less than 30%, and the second positive electrode lithium replenishing agent 230 can decompose to release lithium ions and generate gas.

[0015] 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 collector 10 as a bottom layer, and the positive electrode active material layer 22 is arranged thereon, which can increase the binding force between the positive electrode active material layer 22 and the positive electrode 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 when preparing the positive electrode plate 100, reducing the equipment investment required for humidity control, and reducing the manufacturing cost. In addition, compared with the electrode whose lithium replenishing material is only the first positive electrode lithium replenishing agent, under the condition that the total lithium replenishing amount remains unchanged, the amount of the first positive electrode lithium replenishing agent added in the positive electrode electrode of the present application is lower. Even when the first lithium replenishing layer 21 still contains positive electrode active material, the reduction in the compaction density of the electrode brought about by it is also smaller, the battery impedance is relatively low, and the power is relatively better.

[0016] 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 high-power discharge capability and continuous discharge capability of the battery.

[0017] In the present application, the second positive electrode lithium supplement can only decompose to release lithium ions, because after it decomposes to release 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 supplement can also be called a sacrificial lithium supplement. After the first positive electrode lithium supplement releases lithium ions at a higher voltage, a part of the main structure or lithium desorption products remain 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 supplement can be obtained by the ratio of the first cycle discharge capacity to the first cycle charging capacity of the button battery made of it as the positive electrode active material. Specifically, the test conditions for the first coulombic efficiency of the first positive electrode lithium replenisher are: 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 charging capacity is the first coulombic efficiency.

[0018] In the embodiment of the present application, the first positive electrode lithium supplement agent 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 not limited thereto. Among them, the surface of the first positive electrode lithium supplement agent may or may not have a conductive coating layer, and it is preferred to have a conductive coating layer. In the embodiment of the present application, the second positive electrode lithium supplement agent 230 can be selected from one or more of Li2CO3, Li3N, Li2O2, Li2O, Li2C2O4, Li2C4O4, Li2C3O5, Li2C4O6, etc., but not limited thereto.

[0019] 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 application, they are distinguished by different names / codes. In the embodiment of the present application, each positive electrode active material can be independently selected from one or more of lithium iron phosphate (LFP), lithium iron manganese phosphate (LMFP), lithium manganate (LMO), lithium cobaltate, nickel manganese oxide material (LNMO), nickel cobalt manganese oxide ternary material (NCM), nickel cobalt aluminum oxide ternary material (NCA), lithium-rich lithium manganese oxide 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 iron manganese phosphate usually have a conductive carbon coating.

[0020] In the present application, the first lithium replenishing layer 21 may not contain positive electrode active materials (such as Figure 1A ), and may also contain positive electrode active materials (such as Figure 1B As shown, it can be indicated by reference numeral 211 ). The material selection range of the positive electrode active material 211 can 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 this application.

[0021] In some embodiments of the present application, the first lithium replenishing layer 21 includes a third positive electrode active material having a mass percentage content not exceeding (i.e., less than or equal to) that of the first positive electrode lithium replenishing agent. By not introducing too much of the third positive electrode active material, the reduction in the compaction density of the positive electrode sheet caused by its distribution in the same layer with the first positive electrode lithium replenishing agent 210 can be reduced, and the battery impedance is relatively low, and the power is relatively good.

[0022] In some embodiments of the present application, 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 the third positive electrode active material with a mass percentage of no more than 40% is more conducive to ensuring a higher compaction density of the positive electrode sheet and a lower battery impedance. The presence of an appropriate amount of the binder can ensure the adhesion of the first lithium replenishing layer 21 on the positive electrode current collector 10, and the presence of an appropriate amount of the 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 the conductive agent can independently be 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 4%, 4.5%, 5%, 6%, 7%, 8% or 9%, etc.

[0023] In some embodiments of the present application, the first lithium replenishing layer 21 contains a third positive electrode active material, and its mass percentage can be 10-40%, for example, specifically 12%, 15%, 20%, 25%, 28%, 30%, 35%, or 40%. The first lithium replenishing layer 21 contains an appropriate amount of the third positive electrode active material, so that the first lithium replenishing layer 21 can also contribute a certain capacity in the battery after formation. In addition, the first lithium replenishing layer 21 containing the positive electrode active material is conducive to controlling the coating accuracy and improving the process stability.

[0024] In some other embodiments of the present application, 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 0. In this case, it can still be said that in the first lithium replenishing layer 21, the mass percentage of the first positive electrode replenishing agent 210 is greater than the third positive electrode active material (that is, in the first lithium replenishing layer, the mass percentage of the third positive electrode active material is less than or equal to the mass percentage of the first positive electrode replenishing agent). The first lithium replenishing layer 21 does not contain the third positive electrode active material, which can make the viscosity of the slurry used to form the first lithium replenishing layer 21 more suitable, easier to apply, and make the compaction density of the positive electrode sheet higher, avoiding reducing the battery impedance and power performance.

[0025] In some embodiments of the present application, 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 application, the positive electrode active material layer 22 may not contain the positive electrode lithium replenisher. This can avoid the problem of slurry coating difficulties caused by the positive electrode active material and the positive electrode lithium replenisher being arranged in the same layer, and the problem of reduced pole piece compaction density caused by the poor matching of the particle sizes of the two.

[0026] In some embodiments of the present application, the ratio of the single-sided surface density of the first lithium replenishing layer 21 to the single-sided 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 application, the ratio of the single-sided surface density of the positive electrode active material layer 22 to the single-sided surface density of the coating structure 20 is 0.1-0.9; in some embodiments of the present application, the ratio of the single-sided surface density of the second lithium replenishing layer 23 to the single-sided 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, the energy density of the battery is high, etc. 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.

[0027] In some embodiments of the present application, 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 replenishment capacity is appropriate, and the overall performance of the lithium battery is good. In some embodiments, the single-surface density of the first lithium replenisher layer 21 is 1-20 g / m 2 , for example, 1.5 g / 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 have both high positive electrode gram capacity and first coulomb efficiency, as well as high lithium supplement utilization rate. In the embodiment of the present application, the single surface density of the positive electrode active material layer 22 and the second lithium supplement layer 23 is independently 10-500g / m 2 In the range of, for example, 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 independently 100-500 g / m 2 This is more conducive to their role in providing capacity in the formed battery.

[0028] In some embodiments of the present application, the single-sided surface density of the positive electrode active material layer 22 and / or the second lithium supplement layer 23 is greater than that of the first lithium supplement layer 21. The positive electrode active material layer 22 and the second lithium supplement layer 23 are the main capacity-providing layers of the battery, and their single-sided surface density is higher than that of the first lithium supplement layer 21, which is conducive to ensuring that the energy density and discharge capacity of the battery are high. Accordingly, the single-sided thickness of the positive electrode active material layer 22 and / or the second lithium supplement layer 23 is greater than that of the first lithium supplement layer 21. In the embodiment of the present application, the single-sided thickness of the first lithium supplement layer 21 can be in the range of 0.1-100μm. In some embodiments, the single-sided thickness of the first lithium replenishing layer 21 is 1-20 μm, for example, specifically 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 to ensure the stable existence of the positive active material layer 22 on the positive current collector 10, and does not reduce the reversible capacity of the positive electrode plate 100 and the energy density of the battery cell, while ensuring 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 small during the first charging of the battery. In the embodiment of the present application, the single-sided thickness of the positive active material layer 22 or the second lithium replenishing layer 23 is independently 20-200 μm. An appropriately thick positive electrode active material layer 22 or second lithium supplement layer 23 can ensure that the energy density and discharge capacity of the battery are relatively high.

[0029] In some embodiments of the present application, the ratio of the single-surface surface density of the positive electrode active material layer 22 to the second lithium replenishing layer 23 is in the range of (0.5-2.0). The mass ratio of the positive electrode active material layer 22 to the second lithium replenishing layer 23 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.

[0030] In some embodiments of the present application, 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 formation process, it will not affect the overall second lithium replenishing layer 23 too much to provide capacity. In some embodiments of the present application, 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 can replenish the irreversible consumption of active lithium for the battery while making the gas production of the positive electrode of the battery less and the reversible capacity larger. In some embodiments, the mass ratio is 1-5%.

[0031] In some embodiments of the present application, the total mass proportion of the second positive electrode active material 231 in the second lithium replenishing layer 23 is more than 80%, preferably more than 90%. This is more conducive to ensuring that the reversible capacity provided by the second lithium replenishing layer 23 is higher, thereby ensuring that the reversible capacity of the overall positive electrode plate is higher.

[0032] In the embodiment of the present application, the second lithium supplement layer 23 can be a layer (such as Figure 1A , Figure 1B As shown), it can also be multi-layer (that is, the number of layers ≥ 2, such as Figure 2 When the second lithium supplement layer 23 is a single layer (as shown in Figure 1A , Figure 1B As shown), the second lithium supplement agent 230 may be uniformly dispersed in the second positive electrode active material 231 .

[0033] In some embodiments of the present application, when the second lithium replenishing layer 23 is multi-layered, such as Figure 2 As shown, it may include n layers of second lithium replenishing sublayers, n≥2. Each second lithium replenishing sublayer contains a second positive electrode lithium replenishing agent 230 and a second positive electrode active material 231. In which, from the positive electrode current collector 10 to the first lithium replenishing layer 21 ( Figure 2), the mass proportion of the second lithium replenishing agent 230 and the second positive electrode active material 231 in each second lithium replenishing sub-layer tends to increase.

[0034] 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 a second lithium replenishing layer, a second sublayer L2 of a 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 sublayer 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 sublayer 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 sublayer L n The mass ratio of the second positive electrode lithium supplement 230 to the second positive electrode active material 231 is denoted 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-increase again, 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).

[0035] The second positive electrode lithium replenisher 230 decomposes at a voltage greater than its delithiation potential to produce active lithium ions to replenish the battery, while releasing gas, so it can leave pores at its original position after decomposition, increasing the porosity of each second lithium replenishing sub-layer. The present application controls the mass ratio of the second positive electrode lithium replenisher to the second positive electrode active material in each second lithium replenishing sub-layer to increase in the direction away from the positive electrode current collector 10, which is more conducive to the construction of a smoother exhaust channel, especially conducive to the smooth discharge of the gas generated by the decomposition of the second positive electrode lithium replenisher 230 in the second lithium replenishing sub-layer close to the positive electrode current collector, reducing battery polarization, and making the delithiation potential of the second positive electrode lithium replenisher in each second lithium replenishing sub-layer basically the same, so that the decomposition ratio of the second positive electrode lithium replenisher in each sub-layer is relatively high, and the reduction of battery polarization is also conducive to reducing the overall impedance of the battery and improving the sustainable discharge capacity of the battery. In addition, after the decomposition of this type of lithium supplement, the pores created in each second lithium supplement sublayer also form a gradient pore structure, that is, the number of pores in the second lithium supplement sublayer close to the positive electrode current collector 10 is small and the porosity is small, while the porosity of the second lithium supplement sublayer farther away from the positive electrode current collector 10 is higher. This gradient pore structure helps to 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 the power performance of the battery.

[0036] In some embodiments, the above-mentioned increasing trend specifically increases layer by layer. That is, in the n-layer second lithium replenishing sub-layer, from the positive electrode current collector 10 to the first lithium replenishing layer 21, the mass proportion of the second lithium replenishing agent 230 and the second positive electrode active material 231 in each second lithium replenishing sub-layer increases layer by layer. This is more conducive to the gas generated by the decomposition of the second positive electrode lithium replenishing agent in the second lithium replenishing layer 23 to be discharged more smoothly, and after the decomposition, the second lithium replenishing layer 23 is given a pore structure with a porosity that increases in the direction of the arrow, which is more conducive to reducing the battery impedance.

[0037] In some embodiments of the present application, among the n-layer second lithium supplementation sub-layers, at least two adjacent layers satisfy: A m / (D m / D m-1 )-A m-1 ≥5%; among which, 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 of the m-1th layer, D m is the thickness of the mth second lithium supplement sublayer, m is any integer from 2 to n; on the same side of the positive electrode current collector, the m-1th second lithium supplement sublayer is closer to the positive electrode current collector than the mth second lithium supplement sublayer. That is to say, when the thickness of each second lithium supplement sublayer is roughly the same, at least two adjacent layers of the 1st to nth second lithium supplement 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 replenisher is decomposed, the porosity of at least two adjacent second lithium replenisher sublayers can be clearly distinguished, and the above-mentioned gradient pore structure has a good effect of reducing battery impedance and improving power performance. Further, in some embodiments of the present application, among the n layers of second lithium replenisher sublayers, any two adjacent second lithium replenisher sublayers satisfy: 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.

[0038] In some embodiments, when the thickness of each second lithium supplementing sub-layer is equal (ie, D m / Dm-1 =1), in the n-layer second lithium replenishing sub-layer, the mass ratio difference 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 more than 5%. That is to say: in D m / D m-1 = 1, among the n layers of the second lithium-replenishing sub-layers, any two adjacent layers of the second lithium-replenishing sub-layers satisfy: A m -A m-1 ≥5%, m is any integer from 2 to n. In this way, after the battery is formed, the porosity formed in the second lithium supplement layer 23 increases layer by layer in the direction away from the positive electrode active material layer 22, which is more effective in reducing battery impedance and improving power performance.

[0039] For example, if the mass ratio of the second positive electrode lithium replenisher in the first sublayer L1 of the second lithium replenishing layer 23 to the mass ratio of the second positive electrode lithium replenisher in the second lithium replenishing layer 23 is recorded as A1, the mass ratio of the second positive electrode lithium replenisher in the second sublayer L2 to the mass ratio of the second positive electrode lithium replenisher in the second lithium replenishing layer 23 is recorded as A2, ..., the mass ratio of the second positive electrode lithium replenisher in the nth sublayer L n The mass ratio of the second positive electrode lithium replenishing agent in 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 A n , when the thickness of each second lithium supplementation sublayer is equal, then |A2-A1|, |A3-A2|, ... |A n -A n-1 |are both ≥5%, preferably ≥10%. Wherein, A1 is greater than 0. If the total mass of all the second positive electrode lithium replenishers in the second lithium replenishing layer 23 is recorded as M, the mass of the second positive electrode lithium replenisher in the first sublayer L1 is recorded as m1, the mass of the second positive electrode lithium replenisher in the second sublayer L2 is recorded as m2, ..., the mass of the second positive electrode lithium replenisher in the nth sublayer L n The mass of the second positive electrode lithium supplement in is denoted 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%.

[0040] In the embodiment of the present application, the mass proportion of the second positive electrode active material in each second lithium replenishing sublayer is more than 80%, preferably more than 90%. This can be more conducive to the higher reversible capacity provided by each second lithium replenishing sublayer, thereby ensuring that the reversible capacity of the overall positive electrode sheet is higher. In addition, in some embodiments of the present application, the single-sided surface density of each positive electrode sub-coating may be equal or unequal. Among them, taking the first sublayer 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 sublayer L1 to the total mass of the first sublayer L1 is more than 80%, and further more than 90%.

[0041] In some embodiments of the present application, the above n=2, X2>X1. That is, the second lithium replenishing layer 23 includes two second lithium replenishing sub-layers, wherein the mass ratio of the second lithium replenishing agent 230 and the second positive electrode active material 231 in the second lithium replenishing sub-layer far 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 sub-layer close to the positive electrode current collector 10. In this way, while ensuring that the second lithium replenishing layer 23 has the above-mentioned effects, its preparation is more convenient and time-saving.

[0042] In addition, it should be noted that the first lithium replenishing layer 21 may also be a multilayer with a composition gradient change; the positive electrode active material layer 22 may also be a multilayer with a composition gradient change.

[0043] In the present application, the positive electrode active material layer 22 and the second lithium supplement layer 23 may also independently contain a conductive agent and a binder. The conductive agent in each of the above coatings may be independently 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 independently 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 also independently contain one or more dispersants, wherein each dispersant may be selected from one or more of polyvinyl pyrrolidone (PVP), polyvinyl alcohol (PVA), and the like.

[0044] In the present application, the positive electrode current collector 10 may include but is not limited to aluminum foil, aluminum alloy foil, a polymer film material coated with metal aluminum, or the aforementioned materials coated with carbon on the surface. In some embodiments of the present application, the positive electrode current collector 10 is aluminum foil. In the present application, a coating structure 20 (such as Figure 1A , Figure 1B and Figure 2 As shown in FIG. 1 , a coating structure 20 may also be formed on both sides of the positive electrode current collector 10 .

[0045] Among them, the first lithium replenishing layer 21 can be formed by coating and baking a primer slurry containing a first positive electrode lithium replenishing agent, a conductive agent, a binder, and a solvent; the positive electrode active material layer 22 can be formed by coating and baking a positive electrode slurry containing a first positive electrode active material, a conductive agent, a binder, and a solvent. The coating method may 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 and baking 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. Among them, the type of the second lithium replenishing slurry used corresponds to the total number of sublayers of the second lithium replenishing layer 23.

[0046] The solvents contained in each slurry may be the same or different, and may be independently selected from one or more of pyrrolidones (e.g., N-methylpyrrolidone (NMP), N-ethylpyrrolidone, etc.), cyclic ethers (e.g., tetrahydrofuran, methyltetrahydrofuran), etc., dimethyl sulfoxide, ketones (e.g., acetone, butanone), lactones (e.g., butyrolactone, caprolactone), etc., but are not limited thereto. The solid content of each slurry is not particularly limited, as long as the fluidity and uniformity of the slurry coating are met. Generally, the solid content of the primer slurry may be 10-50%. The solid content of the positive electrode slurry is in the range of 30%-70%.

[0047] 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 second lithium replenishment layer 23 as an example, a second lithium replenishment slurry can be directly applied to the positive electrode slurry (it 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, after the above-mentioned primer slurry is applied to one side surface of the positive electrode current collector 10 and dried to form the first lithium replenishment layer 21, the positive electrode slurry is applied on the first lithium replenishment layer 21 and dried to form the positive electrode active material layer 22, and then the second lithium replenishment slurry is applied on the positive electrode active material layer 22 to dry to form the second lithium replenishment layer 23, and then rolled.

[0048] The embodiment of the present application further provides a lithium battery, which includes the positive electrode plate 100 described above in the embodiment of the present application.

[0049] In some embodiments of the present application, the 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.

[0050] Among them, the negative electrode plate generally includes a negative electrode current collector and a negative electrode material layer arranged 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 application, 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 microspheres, etc. The silicon-based material may include one or more of elemental silicon, silicon alloys, silicon oxides, silicon-carbon composite materials, etc. The tin-based material may include one or more of elemental tin, tin oxides, tin-based alloys, tin-carbon compounds, etc.

[0051] The diaphragm is used to separate the positive electrode sheet and the negative electrode sheet to maintain the insulation and liquid retention characteristics between the two; the diaphragm, the positive electrode sheet and the negative electrode sheet together constitute the battery cell, which is accommodated in the battery shell and is infiltrated by the electrolyte contained in the shell. In some embodiments of the present application, the lithium battery can be assembled by the following method: the positive electrode sheet, the diaphragm and the negative electrode sheet are stacked in sequence to form a battery cell; the battery cell is accommodated in the battery shell, and the electrolyte is injected, and then the battery shell is sealed to obtain a battery. The battery cell can be wound or laminated.

[0052] The separator may use any separator material in the battery, and 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 and triple-layer PP / PE / PP polymer separators, or non-woven fabrics, etc. The electrolyte includes electrolyte salt and organic solvent, wherein the specific types and compositions of electrolyte salt and organic solvent are conventional choices in the battery field and can be selected according to actual needs.

[0053] The embodiment of the present application also provides a device, which includes the above-mentioned lithium battery of the embodiment of the present application. 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 computer, 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 may include a plurality of the above-mentioned 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.

[0054] The technical solution of the present application is further described below in conjunction with a number of specific embodiments.

[0055] Example 1

[0056] A method for preparing a positive electrode sheet, comprising:

[0057] 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 100:50:4.5:4.5:2:240, stirred evenly to obtain a primer slurry, and the primer slurry is sprayed on the surface of the positive electrode current collector - aluminum foil, and then high-temperature baking is performed to volatilize NMP to form an aluminum foil with a first lithium supplement layer. Among them, the single-sided surface density of the first lithium supplement layer is 5.8g / m 2 , the single-side thickness is 4±1μm.

[0058] Lithium iron phosphate (LFP) is mixed evenly 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 is coated on the first lithium supplement layer, and after baking, a single-sided surface density of 100 g / m is formed. 2 , the positive electrode active material layer has a single-sided thickness of 40μm.

[0059] Then, LFP was mixed evenly with a binder PVDF, a carbon nanotube conductive agent, a graphene conductive agent, a second positive electrode lithium supplement lithium oxalate (Li2C2O4), and a 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 positive electrode active material layer and baked to form a single-sided surface density of 100 g / m 2 , a second lithium supplement layer with a single-sided thickness of 40 μm. If double-sided coating is required, repeat the above operations of forming the first lithium supplement layer, the positive electrode active material layer, and the second lithium supplement layer on the other side of the aluminum foil to obtain a double-sided positive electrode sheet.

[0060] Preparation of a lithium battery:

[0061] (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 evenly 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-sided surface density of 100g / m 2 A negative electrode active material layer;

[0062] (2) Battery assembly: The positive electrode sheet, the separator, and the negative electrode sheet are stacked in sequence to obtain a battery cell; the stacked battery cell is then wound and placed in a battery casing, and after assembly and baking, the prepared electrolyte is injected, and the battery casing is sealed and an air bag is reserved to obtain a fully enclosed lithium battery for subsequent electrical performance testing.

[0063] Example 2

[0064] A preparation method of a positive electrode sheet, which is different from Example 1 in that: the second lithium supplement layer includes two sub-layers with equal surface density, and the single-surface surface density of the second lithium supplement layer is still the same as that of Example 1, which is 100 g / m 2 , with a thickness of 40μm; wherein, 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.

[0065] According to the method described in Example 1, the positive electrode sheets of Example 2 are assembled into a full-package lithium battery.

[0066] Example 3

[0067] A preparation of a positive electrode sheet, which is different 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. Among them, the single-sided surface density of the first lithium replenishing layer is 4.0g / m 2 , the single-side thickness is 3±1μm.

[0068] According to the method described in Example 1, the positive electrode sheets of Example 3 are assembled into a full-package lithium battery.

[0069] Example 4

[0070] A preparation of a positive electrode sheet, which is mainly different from Example 1 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 single-side thickness is 4±1μm.

[0071] According to the method described in Example 1, the positive electrode sheets of Example 4 are assembled into a full-package lithium battery.

[0072] Example 5

[0073] A preparation of 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 (the mass proportion of the coating layer material is 3wt%); the second positive electrode lithium replenishing agent in the second lithium replenishing layer is replaced by lithium nitride (Li3N).

[0074] Specifically, the formula of the primer slurry used to form the first lithium replenishing layer is the same as that of Example 1, except that the single-sided surface density of the first lithium replenishing layer is 4.8 g / m 2 , the single-side thickness is 4±1μm.

[0075] The composition and surface density of the positive electrode active material layer are the same as those of Examples 1 and 3.

[0076] The second lithium supplement layer includes two layers with equal surface density, and the single surface density of the second lithium supplement layer is 64g / m 2 The single-side thickness is 26μm; among them, the formula of the lower 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 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.

[0077] According to the method described in Example 1, the positive electrode sheets of Example 5 are assembled into a full-package lithium battery.

[0078] Example 6

[0079] A preparation of a positive electrode sheet, which is mainly different from Example 1 in that:

[0080] 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;

[0081] 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 surface density of the upper and lower second lithium replenishment sublayers is 6: 4, and the sum of the two is 100g / 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.

[0082] According to the method described in Example 1, the positive electrode sheets of Example 6 are assembled into a full-package lithium battery.

[0083] Example 7

[0084] A preparation of a positive electrode plate, which is mainly different from Example 6 in that: the second lithium replenishing layer is a layer, and the mixed slurry used to form the second lithium replenishing layer is obtained by mixing LFP, binder PVDF, carbon nanotube conductive agent, graphene conductive agent, second lithium replenishing agent Li2CO3, and NMP in a mass ratio of 100:2.5:1:0.5:1.4:60. Among them, the single-sided surface density and thickness of the second lithium replenishing layer are the same as those in Example 6. Among them, the single-sided surface density and thickness of the second lithium replenishing layer are the same as those in Example 6.

[0085] According to the method described in Example 1, the positive electrode sheets of Example 7 are assembled into a full-package lithium battery.

[0086] Example 8

[0087] A positive electrode plate, which is different from Example 1 in that the first positive electrode lithium supplement used is Li5FeO4 without a conductive coating layer on the surface.

[0088] Example 9

[0089] A method for preparing a positive electrode sheet comprises:

[0090] 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, and the primer slurry is sprayed on the surface of the positive electrode current collector-aluminum foil, and after baking, a single-sided surface density of 20g / m 2 , the first lithium replenishment layer has a single-sided thickness of 16±1μm.

[0091] The positive electrode slurry with the same formula as Example 1 is coated on the first lithium supplement layer, and after baking, a single-sided surface density of 150g / m 2 , the positive electrode active material layer has a single-sided thickness of 60μm.

[0092] Then, LFP was mixed evenly with a binder PVDF, a carbon nanotube conductive agent, a graphene conductive agent, a second positive electrode lithium supplement lithium oxalate (Li2C2O4), and a 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 positive electrode active material layer and baked to form a single-sided surface density of 30 g / m 2 , a second lithium replenishing layer with a single-side thickness of 12 μm. The single-side surface density of the first lithium replenishing layer is 10% of the sum of the single-side density of the first lithium replenishing layer, the positive electrode active material layer, and the second lithium replenishing layer.

[0093] The above-mentioned operations of forming the first lithium replenishing layer, the positive electrode active material layer, and the second lithium replenishing layer are repeated on the other side of the aluminum foil to obtain a double-sided positive electrode sheet.

[0094] According to the method described in Example 1, the positive electrode sheets of Example 9 are assembled into a full-package lithium battery.

[0095] Example 10

[0096] A method for preparing a positive electrode sheet, comprising:

[0097] 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, and the primer slurry is sprayed on the surface of the positive electrode current collector-aluminum foil, and after baking, a surface density of 50g / m 2 , a first lithium replenishing layer with a thickness of 40±1μm.

[0098] The positive electrode slurry with the same formula as Example 1 was coated on the first lithium supplement layer, and after baking, a single-sided surface density of 375 g / m 2 , a positive electrode active material layer with a single-sided thickness of 150μm.

[0099] Then, LFP was mixed evenly with a binder PVDF, a carbon nanotube conductive agent, a graphene conductive agent, a second positive electrode lithium supplement lithium oxalate (Li2C2O4), and a 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 positive electrode active material layer and baked to form a single-sided surface density of 75g / m 2, a second lithium replenishing layer with a single-sided thickness of 30μm.

[0100] The above-mentioned operations of forming the first lithium replenishing layer, the positive electrode active material layer, and the second lithium replenishing layer are repeated on the other side of the aluminum foil to obtain a double-sided positive electrode sheet.

[0101] Embodiment 11

[0102] A positive electrode sheet, which is mainly different from Example 1 in 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.

[0103] The method for preparing the positive electrode sheet comprises:

[0104] 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 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 the first lithium replenishing layer is formed after baking. Among them, the single-sided surface density of the first lithium replenishing layer is 40.0g / m 2 , the single-side thickness is 16μm.

[0105] The positive electrode slurry with the same formula as Example 1 was coated on the first lithium supplement layer, and after baking, a single-sided surface density of 140 g / m 2 , the positive electrode active material layer has a single-side thickness of 56μm.

[0106] Then, the mixed slurry with the same formula as that of Example 1 was coated on the above-mentioned positive electrode active material layer, and after baking, a single-side surface density of 20 g / m 2 , a second lithium replenishing layer with a single-sided thickness of 8μm.

[0107] According to the method described in Example 1, the positive electrode sheets of Example 11 are assembled into a full-package lithium battery.

[0108] Example 12

[0109] 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 single-sided thickness is 2±1μm; the single-sided surface density of the positive electrode active material layer is 30g / m 2 , the single-sided thickness is 12μm; the single-sided surface density of the second lithium supplement layer is 150g / m 2, the single-sided thickness 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 LFP. Among them, the single-sided surface density of the first lithium replenishing layer is 0.003 of the sum of the single-sided density of the first lithium replenishing layer, the positive electrode active material layer, and the second lithium replenishing layer.

[0110] The preparation method of the positive electrode plate comprises: spraying the primer slurry with the same formula as that of Example 1 on the surface of the positive electrode current collector-aluminum foil, and forming a first lithium supplement layer after baking. The single-surface density of the first lithium supplement layer is 0.5g / m 2 , single-sided thickness is 1μm.

[0111] 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 30 g / m 2 , the positive electrode active material layer has a single-sided thickness of 12μm.

[0112] Then, LFP was mixed evenly with a binder PVDF, a carbon nanotube conductive agent, a graphene conductive agent, a second positive electrode lithium supplement lithium oxalate (Li2C2O4), and a 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 positive electrode active material layer and baked to form a single-sided surface density of 170 g / m 2 , a second lithium replenishing layer with a single-sided thickness of 68μm.

[0113] According to the method described in Example 1, the positive electrode plates of Example 12 are assembled into a full-package lithium battery.

[0114] Embodiment 13

[0115] A positive electrode sheet, the main difference from Example 1 is that the single-sided surface density of the first lithium supplement layer is 2.0g / m 2 The single-sided thickness is 1 μm; the single-sided surface density of the positive electrode active material layer is 18 g / m 2 , the single-sided thickness is 8μm; the single-sided surface density of the second lithium supplement layer is 180g / m 2 , the single-sided thickness is 72μm, and in the slurry used to form the second lithium replenishing layer, the mass of the second lithium replenishing agent lithium oxalate is 1.1% of the mass of LFP. The single-sided surface density of the first lithium replenishing layer is 0.01 of the sum of the single-sided density of the first lithium replenishing layer, the positive electrode active material layer, and the second lithium replenishing layer; the single-sided surface density of the second lithium replenishing layer is 0.9 times the sum of the single-sided density of the first lithium replenishing layer, the positive electrode active material layer, and the second lithium replenishing layer.

[0116] The method for preparing the positive electrode sheet comprises:

[0117] The primer slurry with the same formula as Example 1 is sprayed on the surface of the positive electrode current collector - aluminum foil, and after baking, an aluminum foil with a first lithium supplement layer is formed. The single-sided surface density of the first lithium supplement layer is 2.0 g / m 2 , single-sided thickness is 1μm.

[0118] The positive electrode slurry with the same formula as Example 1 was coated on the first lithium supplement layer, and after baking, a single-sided surface density of 18 g / m 2 , the positive electrode active material layer has a single-sided thickness of 8μm.

[0119] Then, LFP was mixed evenly with a binder PVDF, a carbon nanotube conductive agent, a graphene conductive agent, a second positive electrode lithium supplement lithium oxalate (Li2C2O4), and a 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 positive electrode active material layer and baked to form a single-sided surface density of 180 g / m 2 , a second lithium replenishing layer with a single-sided thickness of 72μm.

[0120] According to the method described in Example 1, the positive electrode sheets of Example 13 are assembled into a fully packaged lithium battery.

[0121] Embodiment 14

[0122] A positive electrode sheet, the main difference from Example 1 is that the single-sided surface density of the positive electrode active material layer is 66g / m 2 The single-sided thickness is 26 μm, and the single-sided surface density of the second lithium supplement layer is 132 g / m 2 , the single-side thickness is 52 μm; the single-side surface density ratio of the positive electrode active material layer to the second lithium supplement layer is 0.5. In addition, in the slurry used to form the second lithium supplement layer, the mass of lithium oxalate is 1.5% of the mass of LFP.

[0123] The preparation method of the positive electrode sheet comprises: spraying a first positive electrode lithium supplement (specifically Li5FeO4 with a carbon coating layer on the surface, the coating layer material accounts for 3wt%) and 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 to form a primer slurry on the surface of the positive electrode current collector-aluminum foil, and after baking, a surface density of 5.8g / m 2 , the first lithium replenishment layer has a thickness of 4 μm.

[0124] 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 66 g / m 2 , the positive electrode active material layer has a single-sided thickness of 26μm.

[0125] Then, LFP was mixed evenly with a binder PVDF, a carbon nanotube conductive agent, a graphene conductive agent, a second positive electrode lithium supplement lithium oxalate (Li2C2O4), and a 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 positive electrode active material layer and baked to form a single-sided surface density of 132 g / m 2 , a second lithium replenishing layer with a single-sided thickness of 52μm.

[0126] According to the method described in Example 1, the positive electrode plates of Example 14 are assembled into a full-package lithium battery.

[0127] Embodiment 15

[0128] A positive electrode sheet, which is mainly different from Example 1 in that: the ratio of the single-surface surface density of the positive electrode active material layer to the second lithium supplement layer is 2.0, wherein the single-surface surface density of the positive electrode active material layer is 132 g / m 2 , the single-sided thickness is 52μm; the single-sided surface density of the second lithium supplement layer is 66g / m 2 , the single-side thickness 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.

[0129] The preparation method of the positive electrode plate includes: spraying the first positive electrode lithium supplement 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 on the surface of the positive electrode current collector-aluminum foil, and forming a first lithium supplement layer after baking. Among them, the single-sided surface density of the first lithium supplement layer is 5.8g / m 2 , the single-side thickness is 4μm.

[0130] The positive electrode slurry with the same formula as Example 1 was coated on the first lithium supplement layer, and after baking, a single-sided surface density of 132 g / m 2 , the positive electrode active material layer has a single-sided thickness of 52μm.

[0131] Then, LFP was mixed evenly with a binder PVDF, a carbon nanotube conductive agent, a graphene conductive agent, a second positive electrode lithium supplement lithium oxalate (Li2C2O4), and a 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 positive electrode active material layer and baked to form a single-sided surface density of 66 g / m 2 , a second lithium replenishing layer with a single-sided thickness of 26μm.

[0132] According to the method described in Example 1, the positive electrode plates of Example 15 are assembled into a full-package lithium battery.

[0133] Example 16

[0134] A positive electrode sheet, the main difference from Example 1 is that the single-sided surface density of the positive electrode active material layer is 34g / m 2 The single-sided thickness is 14 μm, and the single-sided surface density of the second lithium supplement layer is 166 g / m 2 The thickness of the single surface is 66 μm, and the mass of lithium oxalate in the slurry used to form the second lithium supplement layer is 1.2% of the mass of LFP. The ratio of the single surface density of the positive electrode active material layer to the second lithium supplement layer is 0.2.

[0135] The preparation method of the positive electrode plate comprises:

[0136] 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 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 the first lithium replenishing layer is formed after baking. Among them, the single-sided surface density of the first lithium replenishing layer is 5.8g / m 2 , the single-side thickness is 4μm.

[0137] The positive electrode slurry with the same formula as Example 1 was coated on the first lithium supplement layer, and after baking, a single-sided surface density of 34 g / m 2 , the positive electrode active material layer has a single-sided thickness of 14μm.

[0138] Then, LFP was mixed evenly with a binder PVDF, a carbon nanotube conductive agent, a graphene conductive agent, a second positive electrode lithium supplement lithium oxalate (Li2C2O4), and a 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 positive electrode active material layer and baked to form a single-sided surface density of 166 g / m 2 , a second lithium replenishing layer with a single-sided thickness of 66μm.

[0139] According to the method described in Example 1, the positive electrode plates of Example 16 are assembled into a full-package lithium battery.

[0140] Embodiment 17

[0141] The main difference between Example 17 and Example 1 is that the single-sided surface density of the positive electrode active material layer is 20 g / m 2 , the single-sided thickness is 8μm; the single-sided surface density of the second lithium supplement layer is 180g / m 2, the single-side thickness 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.

[0142] The preparation of the positive electrode sheet includes:

[0143] 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 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 the first lithium replenishing layer is formed after baking. Among them, the single-sided surface density of the first lithium replenishing layer is 5.8g / m 2 , the single-side thickness is 4μm.

[0144] The positive electrode slurry with the same formula as Example 1 is coated on the first lithium supplement layer, and after baking, a single-sided surface density of 20 g / m 2 , the positive electrode active material layer has a single-sided thickness of 8μm.

[0145] Then, LFP was mixed evenly with a binder PVDF, a carbon nanotube conductive agent, a graphene conductive agent, a second positive electrode lithium supplement lithium oxalate (Li2C2O4), and a 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 positive electrode active material layer and baked to form a single-sided surface density of 180 g / m 2 , a second lithium replenishing layer with a single-sided thickness of 72μm.

[0146] According to the method described in Example 1, the positive electrode plates of Example 17 are assembled into a full-package lithium battery.

[0147] Embodiment 18

[0148] The main difference between Example 18 and Example 1 is that in the positive electrode sheet of Example 18, the single-sided surface density of the positive electrode active material layer is 159 g / m 2 , the single-sided thickness is 64μm; the single-sided surface density of the second lithium supplement layer is 41g / m 2 , the single-side thickness is 16μm; in the second lithium replenishing layer, the total mass of the second lithium replenishing agent is 5% of the total mass of LFP. Among them, the single-side surface density of the second lithium replenishing layer is 0.2 times the sum of the single-side density of the first lithium replenishing layer, the positive electrode active material layer, and the second lithium replenishing layer.

[0149] The preparation of the positive electrode sheet includes:

[0150] 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 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 the first lithium replenishing layer is formed after baking. Among them, the single-sided surface density of the first lithium replenishing layer is 5.8g / m 2 , the single-side thickness is 4μm.

[0151] The positive electrode slurry with the same formula as Example 1 was coated on the first lithium supplement layer, and after baking, a single-sided surface density of 159 g / m 2 , the positive electrode active material layer has a single-sided thickness of 64μm.

[0152] Then, LFP was mixed evenly with a binder PVDF, a carbon nanotube conductive agent, a graphene conductive agent, a second positive electrode lithium supplement lithium oxalate (Li2C2O4), and a 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 positive electrode active material layer and baked to form a single-sided surface density of 41g / m 2 , a second lithium replenishing layer with a single-sided thickness of 16μm.

[0153] According to the method described in Example 1, the positive electrode plates of Example 18 are assembled into a full-package lithium battery.

[0154] Embodiment 19

[0155] The main difference between Example 19 and Example 1 is that in the positive electrode sheet of Example 19, the single-sided surface density of the positive electrode active material layer is 178 g / m 2 , the single-sided thickness is 71μm; the single-sided surface density of the second lithium supplement layer is 22g / m 2 , the single-side thickness is 9μm; in the second lithium replenishing layer, the total mass of the second lithium replenishing agent is 10% of the total mass of LFP. Among them, the single-side surface density of the second lithium replenishing layer is 0.11 times the sum of the single-side density of the first lithium replenishing layer, the positive electrode active material layer, and the second lithium replenishing layer.

[0156] The preparation of the positive electrode sheet includes:

[0157] 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 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 the first lithium replenishing layer is formed after baking. The single-sided surface density of the first lithium replenishing layer is 5.8g / m 2 , the single-side thickness is 4μm.

[0158] The positive electrode slurry with the same formula as Example 1 was coated on the first lithium supplement layer, and after baking, a single-sided surface density of 178 g / m 2 , the positive electrode active material layer has a single-sided thickness of 71μm.

[0159] Then, LFP was mixed evenly with a binder PVDF, a carbon nanotube conductive agent, a graphene conductive agent, a second positive electrode lithium supplement lithium oxalate (Li2C2O4), and a 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 positive electrode active material layer and baked to form a single-sided surface density of 22 g / m 2 , a second lithium replenishing layer with a single-sided thickness of 9μm.

[0160] According to the method described in Example 1, the positive electrode plates of Example 19 are assembled into a full-package lithium battery.

[0161] Embodiment 20

[0162] The main difference between Example 20 and Example 1 is that in the positive electrode sheet of Example 20, in the second lithium replenishing layer, the total mass of the second lithium replenishing agent is 0.5% of the total mass of LFP; the single-sided surface density of the first lithium replenishing layer is 9.5g / m 2 , the single-side thickness is 7μm.

[0163] The preparation of the positive electrode sheet includes:

[0164] 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 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 the first lithium replenishing layer was formed after baking. The single-sided surface density of the first lithium replenishing layer is 9.5g / m 2 , the single-side thickness is 7μm.

[0165] The positive electrode slurry with the same formula as Example 1 is coated on the first lithium supplement layer, and after baking, a single-sided surface density of 100 g / m 2 , the positive electrode active material layer has a single-sided thickness of 40μm.

[0166] Then, LFP was mixed evenly with a binder PVDF, a carbon nanotube conductive agent, a graphene conductive agent, a second positive electrode lithium supplement lithium oxalate (Li2C2O4), and a 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 positive electrode active material layer and baked to form a single-sided surface density of 100 g / m 2 , a second lithium replenishing layer with a single-sided thickness of 40μm.

[0167] According to the method described in Example 1, the positive electrode plates of Example 20 are assembled into a full-package lithium battery.

[0168] Embodiment 21

[0169] The main difference between Example 21 and Example 1 is that in the positive electrode sheet of Example 21, in the second lithium replenishing layer, the total mass of the second lithium replenishing agent is 0.2% of the total mass of the positive electrode active material; the single-sided surface density of the first lithium replenishing layer is 10.0 g / m 2 , thickness is 8μm.

[0170] The preparation of the positive electrode sheet includes:

[0171] 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 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 the first lithium replenishing layer was formed after baking. The single-sided surface density of the first lithium replenishing layer is 10.0g / m 2 , thickness is 8μm.

[0172] The positive electrode slurry with the same formula as Example 1 is coated on the first lithium supplement layer, and after baking, a single-sided surface density of 100 g / m 2 , the positive electrode active material layer has a single-sided thickness of 40μm.

[0173] Then, LFP was mixed evenly with a binder PVDF, a carbon nanotube conductive agent, a graphene conductive agent, a second positive electrode lithium supplement lithium oxalate (Li2C2O4), and a 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 positive electrode active material layer and baked to form a single-sided surface density of 100 g / m 2, a second lithium replenishing layer with a single-sided thickness of 40μm.

[0174] According to the method described in Example 1, the positive electrode sheets of Example 21 are assembled into a fully packaged lithium battery.

[0175] In order to highlight the beneficial effects of the present application, the present application also provides the following comparative examples 1-4.

[0176] Comparative Example 1

[0177] A preparation method for a non-lithium supplemented positive electrode sheet includes: mixing lithium iron phosphate LFP, a binder PVDF, carbon nanotubes, 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 200g / m 2 The positive electrode coating is then coated on the other side of the aluminum foil and dried to obtain a double-sided positive electrode sheet.

[0178] According to the method described in Example 1, the positive electrode sheet of Comparative Example 1 was assembled into a full-package lithium battery.

[0179] Comparative Example 2

[0180] A positive electrode plate, which is different from the embodiment 1 in that only a mixed layer containing both LFP and a first positive electrode lithium replenisher is provided on the aluminum foil.

[0181] The preparation of the positive electrode sheet includes: mixing LFP, binder PVDF, carbon nanotube conductive agent, graphene conductive agent, first positive electrode lithium supplement agent (same as in 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-sided surface density of 200g / m 2 of the positive electrode coating.

[0182] According to the method described in Example 1, the positive electrode sheets of Comparative Example 2 were assembled into a fully packaged lithium battery.

[0183] Comparative Example 3

[0184] A positive electrode plate, which is different from Example 1 in that only a mixed layer containing both LFP and a second positive electrode lithium replenisher is provided on the aluminum foil.

[0185] The preparation of the positive electrode sheet includes: mixing LFP, a binder PVDF, carbon nanotubes, graphene, a second positive electrode lithium supplement Li2C2O4, and a 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 the aluminum foil current collector to form a single-side surface density of 200g / m 2 positive electrode mixed layer.

[0186] According to the method described in Example 1, the positive electrode sheets of Comparative Example 3 were assembled into a fully encapsulated lithium battery.

[0187] Comparative Example 4

[0188] A positive electrode plate, which is different 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 arranged on the aluminum foil.

[0189] LFP, binder PVDF, carbon nanotubes, graphene, the first positive electrode lithium supplement, the second positive electrode lithium supplement 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 an aluminum foil, and after baking, 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 baked to obtain a double-sided positive electrode sheet.

[0190] According to the method described in Example 1, the positive electrode sheets of Comparative Example 4 were assembled into a fully encapsulated sodium battery.

[0191] Comparative Example 5

[0192] A positive electrode sheet is different from Example 1 in that: there is no second lithium supplement layer on the positive electrode active material layer, and the single-surface surface density of the positive electrode active material layer is equal to the sum of the single-surface surface densities of the positive electrode active material layer and the second lithium supplement layer in Example 1.

[0193] The preparation of the positive electrode plate includes: (1) mixing the first positive electrode lithium supplement (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 100:50:4.5:4.5:2:240, 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 supplement layer. The single-sided surface density of the first lithium supplement layer is 11.6g / m 2, the single-sided thickness 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 first lithium supplement layer, and after drying, a single-sided surface density of 200g / m 2 positive electrode active material layer.

[0194] According to the method described in Example 1, the positive electrode sheets of Comparative Example 5 were assembled into a fully encapsulated lithium battery.

[0195] Comparative Example 6

[0196] 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.

[0197] The preparation method of the positive electrode plate comprises:

[0198] The LFP, binder PVDF, carbon nanotubes, graphene, the second positive electrode lithium supplement Li2C2O4, and solvent NMP are uniformly mixed 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 is coated on an aluminum foil current collector, and after drying, a single-sided surface density of 200 g / m 2 The first material layer.

[0199] The first positive electrode lithium supplement agent (same as in Example 1) is 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 is coated on the first material layer, and after drying, a single-sided surface density of 5.8 g / m is formed. 2 The second material layer.

[0200] Comparative Example 7

[0201] A preparation of a positive electrode, 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.

[0202] 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 operation of forming the positive electrode material layer on the other side of the aluminum foil, and then roll-press to obtain the positive electrode.

[0203] According to the method described in Example 1, the positive electrode of Comparative Example 7 was assembled into a fully encapsulated lithium battery.

[0204] In order to strongly support the beneficial effects brought by the technical solution of the present application, the full-package lithium batteries of the above embodiments or comparative examples were subjected to the following performance tests:

[0205] a. Positive electrode gram capacity test: At room temperature (25±3℃), charge the above batteries at 1 / 3C constant current and constant voltage to an upper limit voltage of 4.6V (C is the battery capacity) for formation, and record the first charge capacity (i.e. the charge capacity during formation). After aging (the aging procedure is 100% SOC state stored at 45℃ for 48h), discharge each battery for the first time at 1 / 3C to a lower limit voltage of 2.0V, and calculate the first discharge capacity and average discharge voltage. Then the positive electrode gram capacity = first discharge capacity / total mass of positive electrode active materials; the mass energy density of the battery = first discharge capacity × average discharge voltage / mass of the battery.

[0206] b. Cycle performance test: At room temperature (25±3°C), charge each aged battery at 1 / 3C constant current and constant voltage to an upper limit voltage of 3.8V, and then discharge at 1 / 3C to a lower limit voltage of 2.0V. Repeat the above charge and discharge steps 500 times, and record the capacity retention rate after 500 cycles. Among them, the capacity retention rate after 500 cycles = the discharge capacity of the 500th cycle / the discharge capacity of the first discharge after aging.

[0207] c. Battery DCIR test: At room temperature (25±3℃), charge the aged batteries at 1 / 3C constant current to an upper voltage limit of 3.8V, and then discharge at 1 / 3C to a lower voltage limit of 2.0V. After 3 cycles, charge at 1 / 3C constant current to 50% SOC at 25℃, record the battery voltage after standing for 1 hour as V1; then discharge at 1.5C for 30s, record the battery voltage after the discharge as V2, where DCIR = (V1-V2) / 1.5C.

[0208] d. Utilization rate test of lithium supplement materials:

[0209] Prepare non-lithium-supplemented batteries corresponding to the lithium-supplemented batteries of the embodiments and comparative examples of the present application (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 process of each non-lithium-supplemented battery and the corresponding lithium-supplemented battery is basically the same, the difference is that: no lithium supplement agent is added to the positive electrode of the non-lithium-supplemented battery.

[0210] Then, at room temperature (25±3°C), each of the above batteries is charged at a constant current and constant voltage of 1 / 3C to an upper limit voltage of 4.6V for formation, and discharged at 1 / 3C to a lower limit voltage of 2.0V after aging. The discharge capacity of each lithium-supplemented battery is recorded as C1, and the discharge capacity of the non-lithium-supplemented battery corresponding to each lithium-supplemented battery is recorded as C2. Then, the utilization rate of the lithium-supplemented material = (C1-C2) / (mass of the lithium-supplemented material × theoretical gram capacity of the lithium-supplemented material).

[0211] The relevant test results are summarized in Table 1 below.

[0212] Table 1

[0213]

[0214] From the comparison of Example 1 and Comparative Examples 1-5 in Table 1, it can be learned that when the positive electrode of the battery does not contain a lithium supplement material (Comparative Example 1), the positive electrode capacity and mass energy density of the battery are both low, and the DCIR value is high. While the positive electrode contains only one type of positive electrode lithium supplement (such as Comparative Examples 2, 3, and 5), or the positive electrode contains two types of positive electrode lithium supplements but they are not distributed as in Comparative Examples 4 and 6 of Example 1 of the present application, 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 supplement material is not high. While in the case of the same positive electrode active material, Example 1 of the present application introduces the above-mentioned first positive electrode lithium supplement and the second positive electrode lithium supplement into the positive electrode of the lithium battery at the same time, and arranges them in the manner required by the present application, the positive electrode capacity, the utilization rate of the lithium supplement material is 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 capacity and continuous discharge capacity 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 supplementation layers, also has similar effects, and the effects are even better than those of Example 1. In addition, the comparison between Comparative Example 7 and Example 4 also reveals similar phenomena to those between Example 1 and Comparative Example 1.

[0215] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

Claims

1. A positive electrode sheet, characterized in that: It includes a positive electrode current collector and a coating structure arranged on at least one side of the positive electrode current collector, wherein the coating structure includes 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.

2. The positive electrode sheet according to claim 1, characterized in that: The first positive electrode lithium replenisher 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 is selected from one or more of Li2CO3, Li3N, Li2O2, Li2O, Li2C2O4, Li2C4O4, Li2C3O5, and Li2C4O6.

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

9.

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

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

6. The positive electrode sheet 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 to the single-surface density of the second lithium supplementing layer is in the range of (0.5-2.0).

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

8. The positive electrode sheet according to any one of claims 1 to 7, characterized in that: The thickness of a single surface of the positive electrode active material layer or the second lithium replenishing layer is independently 20-200 μm.

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

10. The positive electrode sheet according to any one of claims 1 to 9, characterized in that: The first lithium replenishing layer includes 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 according to any one of claims 1 to 10, characterized in that: In the second lithium replenishing layer, the total mass of the second positive electrode lithium replenishing agent is 0.5%-5% of the total mass of the second positive electrode active material; preferably, in the second lithium replenishing layer, the total mass percentage of the second positive electrode active material is above 80%, and more preferably above 90%.

12. The positive electrode sheet according to any one of claims 1 to 11, characterized in that: The second lithium replenishing layer includes n second lithium replenishing sublayers, 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 from the positive electrode current collector to the first lithium replenishing layer.

13. The positive electrode sheet according to any one of claims 1 to 12, characterized in that: The second lithium replenishing layer includes n second lithium replenishing sublayers, 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 to the first lithium replenishing layer.

14. The positive electrode sheet according to claim 12 or 13, 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 replenishing agent in the m-1th second lithium replenishing sublayer to the total second positive electrode lithium replenishing agent in the second lithium replenishing layer, 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-replenishing sublayer of the m-1th layer, 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.

15. The positive electrode sheet according to any one of claims 1 to 14, characterized in that: The content of the lithium supplement agent in the positive electrode active material layer is less than or equal to 1%.

16. A lithium battery, characterized in that: Comprising the positive electrode sheet as described in any one of claims 1 to 15.

17. A device, characterized in that: The device comprises the lithium battery as claimed in claim 16, wherein the device is an electrical device or an energy storage system.

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