Positive electrode, lithium battery and device

Abstract

The invention provides a positive electrode, a lithium battery and a device. The positive electrode comprises a positive electrode current collector and a lithium supplement layer and a positive electrode material layer which are sequentially stacked on at least one side of the positive electrode current collector, the lithium supplement layer contains a first positive electrode lithium supplement agent, the positive electrode material layer contains a positive electrode active material and a second positive electrode lithium supplement agent, the first coulombic efficiency of the first positive electrode lithium supplement agent is less than 30%, and the second coulombic efficiency of the second positive electrode lithium supplement agent is less than 30%. And the second positive electrode lithium supplement agent can be decomposed to generate gas. The first positive electrode lithium supplement agent and the second positive electrode lithium supplement agent are simultaneously introduced into the positive electrode and are arranged in a layered manner, so that the power performance of the battery can be improved while the impedance of the battery is not obviously increased.

Description

Technical Field

[0001] The present application relates to the technical field of lithium-ion batteries, and in particular to a positive electrode, 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 in the lithium battery and reduce 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 using highly chemically active metallic lithium to directly pre-lithiate the negative electrode, positive electrode lithium replenishment is safer and more compatible with existing battery preparation processes.

[0003] Among them, the positive electrode lithium replenishment technology includes introducing a positive electrode lithium replenisher that can perform an irreversible lithium delithiation reaction during the first charging process into the positive electrode of the battery to replenish active lithium ions for the lithium battery. Positive electrode lithium replenishers are mainly divided into two categories. The first category is a lithium-rich material with a low first coulomb efficiency. After removing lithium ions at a certain voltage, a part of the main structure or delithiation product remains on the positive electrode side; the second category is a sacrificial lithium replenisher that can decompose to produce lithium ions and gas at a certain voltage. However, there are certain problems with the separate use of these two types of positive electrode lithium replenishers in batteries. For example, when using the first type of positive electrode lithium replenisher, the positive electrode active material is mixed with the first type of positive electrode lithium replenisher, which will increase the positive electrode liquid phase diffusion impedance and thus reduce the battery power performance. 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, and the gas generated by its decomposition is difficult to be discharged smoothly, and the residual gas will also increase the battery impedance and reduce the battery power performance.

[0004] Therefore, it is necessary to develop a solution that can take into account both good positive electrode lithium replenishment effect and battery power performance. Summary of the invention

[0005] In view of this, the present application introduces for the first time a lithium supplement material with low coulombic efficiency and a sacrificial lithium supplement agent that can decompose and produce gas into the positive electrode of the battery, and through the reasonable arrangement of the distribution positions of the two, the battery can have both high battery energy density and good battery power performance.

[0006] Specifically, the first aspect of the present application provides a positive electrode, including a positive electrode current collector and a lithium replenishing layer and a positive electrode material layer stacked in sequence on at least one side of the positive electrode current collector, wherein the lithium replenishing layer contains a first positive electrode lithium replenishing agent, and the positive electrode material layer contains a positive electrode active material and a second positive electrode lithium replenishing agent, 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 produce gas.

[0007] In the above-mentioned battery positive electrode provided in 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 arranged in layers as above, which can reduce the problems of large battery impedance and poor power performance caused by using the first and second positive electrode lithium replenishers alone, so that the battery has both high energy density and good power performance.

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

[0009] Due to the use of the above-mentioned positive electrode, the lithium battery can have both high energy density and good power performance.

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

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

[0012] Figure 2 Another schematic diagram of the structure of the positive electrode 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 1 and Figure 2 The embodiment of the present application provides a positive electrode 100, including a positive electrode current collector 10, and a lithium replenishing layer 20 and a positive electrode material layer 30 stacked in sequence on at least one side of the positive electrode current collector 10, that is, on the same side of the positive electrode current collector 10, the lithium replenishing layer 20 is closer to the positive electrode current collector 10 relative to the positive electrode material layer 30, and the positive electrode material layer 30 is farther away from the positive electrode current collector 10 relative to the lithium replenishing layer 20. Among them, the lithium replenishing layer 20 contains a first positive electrode lithium replenishing agent 201, and the positive electrode material layer 30 contains a positive electrode active material 302 and a second positive electrode lithium replenishing agent 301; the first coulomb efficiency of the first positive electrode lithium replenishing agent 201 is less than 30%, and the second positive electrode lithium replenishing agent 301 can decompose to release lithium ions and generate gas.

[0015] The above-mentioned positive electrode 100 contains two types of positive electrode lithium replenishers at the same time, and the second positive electrode lithium replenisher 301 that can decompose and produce gas is arranged in the positive electrode material layer 30 away from the positive electrode current collector 10, and the first positive electrode lithium replenisher 201 with low first coulomb efficiency is arranged in the lithium replenishing layer 20 close to the positive electrode current collector 10. On the one hand, compared with the existing positive electrode having only a positive electrode material layer, under the condition that the total lithium replenishment capacity remains unchanged, two types of positive electrode lithium replenishers are jointly introduced into the positive electrode of the present application, the addition amount of the second positive electrode lithium replenisher is reduced, and the decomposition gas production thereof is also reduced accordingly; on the other hand, because the positive electrode material layer 30 containing the second positive electrode lithium replenisher is arranged on the surface of the positive electrode 100 and away from the positive electrode current collector 10, the discharge path of the gas released by its decomposition is shortened, which is more conducive to gas discharge. In this way, the battery polarization is reduced during its decomposition process, the decomposition ratio and utilization rate of the second positive electrode lithium replenisher are guaranteed, and the lithium replenishment utilization rate of the first positive electrode lithium replenisher is also guaranteed. At the same time, less gas remains in the positive electrode 100, the battery impedance is also reduced, and the power performance is improved.

[0016] The commonly used particle size range of the first positive electrode lithium replenisher is within the range of 3-10μm. In the existing positive electrode with only a mixed layer containing the first positive electrode lithium replenisher and the positive electrode active material, the particle size matching degree of the first positive electrode lithium replenisher and the positive electrode active material in the mixed layer is not high and usually cannot form a close stacking, which will reduce the compaction density of the positive electrode sheet and affect the battery energy density. Compared with the existing positive electrode with only a mixed layer containing the first positive electrode lithium replenisher and the positive electrode active material, under the condition that the total lithium replenishment amount remains unchanged, two types of positive electrode lithium replenishers are introduced into the positive electrode of the present application, and the amount of the first positive electrode lithium replenisher added is also reduced. Correspondingly, the impact of reducing the compaction density of the positive electrode brought about by it is also reduced. In addition, the conductivity of the first positive electrode lithium replenisher after releasing active lithium ions is generally good. Setting it in the lithium replenisher layer 20 in contact with the positive electrode current collector 10 is also conducive to ensuring that the conductive network of the overall positive electrode is good, so that the utilization rate of the lithium replenisher is improved, while reducing the battery impedance and improving the battery power performance.

[0017] Therefore, in the above-mentioned positive electrode of the embodiment of the present application, the first and second positive electrode lithium supplements are arranged in layers as above, which can produce a synergistic effect between the two types of lithium supplements and between the two types of lithium supplements and the positive electrode active material of the battery, so that the lithium supplement utilization rate of the two types of lithium supplements is improved, the energy density of the battery is improved, and at the same time the impedance of the battery is reduced and the power performance is improved.

[0018] It should be noted that the second positive electrode lithium replenisher can decompose to release lithium ions. Since the main structure does not exist after it decomposes to release lithium ions and gas, the lithium ions cannot be inserted back into it. This type of lithium replenisher can also be called a sacrificial lithium replenisher. Therefore, for this type of positive electrode lithium replenisher, there is no concept of "first coulomb efficiency". The first positive electrode lithium replenisher can release lithium ions at a higher voltage, and a part of the main structure or lithium desorption products remain in the positive electrode. It has a certain ability to reinsert lithium ions, but its ability to reinsert lithium ions is poor, that is, its ability to reversibly remove / insert lithium ions is poor, and the first coulomb efficiency is low (less than 30%), which is much lower than the first coulomb efficiency of the positive electrode active material (generally above 60%). Among them, the first coulomb efficiency of the first positive electrode lithium replenisher can be obtained by the ratio of the first cycle discharge capacity to the first cycle charging capacity of the buckle made of it as a positive electrode active material. Specifically, the conditions for the first coulombic efficiency test of the first positive electrode lithium replenisher are: the buckling specification is CR2032, the positive electrode foil is carbon-coated aluminum foil, the positive electrode formula is the first positive electrode 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.

[0019] In the embodiment of the present application, the first positive electrode lithium supplement 201 may include one or more of Li6CoO4, Li2MoO3, Li5FeO4, Li6MnO4, Li2NiO2, Li2CuO2, Li3PO4, Li4SiO4, Li2SiO3, Li3VO4, Li2VO3, Li5ReO6, Li2RuO3, Li2MnO3, Li2MoO3, Li2S, LiF, etc., but is not limited thereto. In the embodiment of the present application, the second positive electrode lithium supplement 301 may include one or more of Li2CO3, Li3N, Li2O2, Li2O, Li2C2O4, Li2C4O4, Li2C3O5, Li2C4O6, etc., but is not limited thereto.

[0020] The surface of the first positive electrode lithium supplement may or may not have a conductive coating layer. In some embodiments, the surface of the first positive electrode lithium supplement has a conductive coating layer. At this time, the first positive electrode lithium supplement has good conductivity, which is conducive to ensuring a good conductive network of the lithium supplement layer 20, reducing battery impedance, and improving battery power performance.

[0021] In some embodiments of the present application, in the positive electrode material layer 30, the positive electrode active material 302 can be selected from one or more of lithium iron phosphate, lithium iron manganese phosphate, lithium manganate, lithium cobaltate, nickel lithium manganate material, lithium cobalt manganate ternary material, nickel cobalt aluminum lithium ternary material, lithium-rich lithium manganate material, etc. These positive electrode active materials can be undoped or modified by doping, and their surfaces can have a conductive coating layer or no conductive coating layer. Generally, lithium iron phosphate and lithium iron manganese phosphate materials usually have a conductive carbon coating layer.

[0022] In some embodiments of the present application, in the positive electrode material layer 30, the particle size of the second positive electrode lithium supplement 301 is smaller than the average particle size of the positive electrode active material 302. In some embodiments of the present application, in the positive electrode material layer 30, the Dv50 of the second positive electrode lithium supplement 301 is 20-500nm, and the Dv50 of the positive electrode active material 302 is 0.2-5μm. In this way, the second positive electrode lithium supplement 301 with a smaller particle size is arranged in the same layer as the positive electrode active material 302 with a larger particle size. The particle size matching degree between the two is high, and a tight stacking can be formed, which will not reduce the compaction density and energy density of the positive electrode 100. In addition, the pore size produced by the second positive electrode lithium supplement 301 in this particle size range after decomposition and release of active lithium is suitable, which can make the positive electrode material layer 30 have suitable pores, thereby helping to reduce the overall impedance of the battery and improve the power performance. Among them, Dv50 refers to the particle size corresponding to the cumulative volume fraction reaching 50% in the particle size distribution based on the particle volume.

[0023] In the present application, the lithium replenishing layer 20 may not contain positive electrode active materials, or may contain positive electrode active materials. In the embodiment of the present application, the lithium replenishing layer 20 may contain the following components in percentage by weight: 50%-90% of the first positive electrode lithium replenishing agent, 0-40% of the second positive electrode active material, 0.5-10% of the binder, and 0.5-10% of the conductive agent. Among them, the selection range of the second positive electrode active material can refer to the description of the positive electrode active material in the positive electrode material layer 30 in the previous text of this application. The second positive electrode active material and the positive electrode active material in the positive electrode material layer 30 may be the same or different materials. Specifically, the mass percentage of the first positive electrode lithium replenishing agent in the lithium replenishing layer 20 may be 55%, 60%, 65%, 70%, 75%, 80%, 85% or 90%, etc. The mass percentage of the binder or the conductive agent can be independently 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%.

[0024] In some embodiments of the present application, when the content of the second positive electrode active material in the lithium replenishing layer 20 is 0, it is considered that the lithium replenishing layer 20 does not contain the positive electrode active material. In this way, the problem of increasing the viscosity of the positive electrode slurry and making it difficult to coat caused by directly mixing the first positive electrode lithium replenishing agent with the positive electrode active material is avoided, and the impact of deteriorating the compaction density of the positive electrode due to the poor matching degree of the particle sizes of the two is also greatly reduced. It also avoids the problem of increasing the positive electrode liquid phase diffusion impedance and slowing down the liquid phase transmission speed of lithium ions caused by its dispersion in the positive electrode slurry, which is conducive to reducing the battery impedance.

[0025] In some embodiments of the present application, the single-sided surface density of the positive electrode material layer 30 is greater than the single-sided surface density of the lithium supplement layer 20. The positive electrode material layer 30 is the main capacity-providing layer of the battery, and its single-sided surface density is higher than that of the lithium supplement layer 20, which is conducive to ensuring that the energy density and discharge capacity of the battery are high. Taking the lithium supplement layer 20 as an example, the "single-sided surface density" here refers to the surface density of the lithium supplement layer 20 on one side of the positive current collector 10, rather than the sum of the surface densities of the two lithium supplement layers 20 located on both sides of the positive current collector 10.

[0026] In the embodiment of the present application, the single surface density of the lithium supplement layer 20 is 0.5-50 g / m 2 This can ensure that the lithium replenishing capacity of the first positive electrode lithium replenishing agent is appropriate to a certain extent, and ensure that the overall performance of the lithium battery is good. It will not cause the lithium replenishing effect of the battery to be insignificant due to insufficient lithium replenishing capacity of the first positive electrode lithium replenishing agent, nor will it cause the lithium replenishing amount to exceed the reasonable level of the current battery design due to excessive addition of the first positive electrode lithium replenishing agent. In some embodiments, the single-sided surface density of the lithium replenishing layer 20 is 0.5-20g / m 2 , for example, 0.8 g / m 2 1.0g / m 2 , 1.2g / m 2 , 1.5g / m 2 , 2g / m 2 , 2.5g / m 2 3.0g / m 2 4.0g / m 2 5.0g / m 2 , 6.0g / m 2 , 7.0g / m 2 , 8.0g / m 2 , 9.0g / m 2 10.0g / m 2 , 15.0g / m 2 or 20.0g / m 2 This will help the battery to have both high positive electrode gram capacity and initial coulombic efficiency, as well as higher lithium supplement utilization.

[0027] In the embodiment of the present application, the single surface density of the positive electrode material layer 30 is 50-1000 g / m 2 , for example, 60g / m 2 , 80g / m 2 , 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 material layer 30 is 100-500 g / m 2 .

[0028] In the embodiment of the present application, the thickness of a single surface of the lithium supplement layer 20 is smaller than the thickness of a single surface of the positive electrode material layer 30. This is also conducive to ensuring a high energy density of the battery.

[0029] In the embodiment of the present application, the single-sided thickness of the lithium replenishing layer 20 can be in the range of 0.1-100 μm, and can further be 0.1-50 μm, or 0.5-20 μm, etc. In some embodiments, the single-sided thickness of the lithium replenishing layer 20 is 0.5-10 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 or 9 μm, etc. In this case, the lithium replenishing layer 20 containing the first positive electrode lithium replenishing agent can ensure that the gas production of the positive electrode is small and the battery impedance is low during the first charging of the battery, and the total capacity of the positive electrode 100 and the energy density of the battery cell will not be reduced due to its excessive thickness. In an embodiment of the present application, the single-sided thickness of the positive electrode material layer 30 may be in the range of 25-500 μm, for example, 30 μm, 50 μm, 80 μm, 100 μm, 120 μm, 150 μm, 200 μm, 220 μm, 250 μm, 300 μm, 350 μm, 400 μm, or 450 μm, etc.; in some embodiments, the single-sided thickness of the positive electrode material layer 30 is 50-250 μm.

[0030] In the embodiment of the present application, in the positive electrode material layer 30, the total mass of the second positive electrode lithium supplement 301 is 0.5%-5% of the total mass of the positive electrode active material 302, for example, specifically 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%. This can ensure that the second positive electrode lithium supplement 301 can replenish the irreversible consumption of active lithium in the battery while not making the reversible capacity of the positive electrode of the battery too small or the gas production of the positive electrode too much. Among them, whether the positive electrode material layer 30 is a layer (such as Figure 1 as shown) or multiple layers (i.e., the number of layers ≥ 2, such as Figure 2 In some embodiments, in the positive electrode material layer 30 , the total mass of the second positive electrode lithium supplement 301 is 1-5% of the total mass of the positive electrode active material 302 .

[0031] In the embodiment of the present application, in the positive electrode 100, the ratio of the lithium replenishing capacity that can be provided by the first positive electrode lithium replenisher 201 and the second positive electrode lithium replenisher 301 is (0.2-2): 1. In this case, it is more conducive to improving the comprehensive performance of the lithium battery, especially to reducing the DCIR value of the battery and improving the utilization rate of the lithium replenisher. Among them, the lithium replenishing capacity provided by each lithium replenisher is equal to the product of its mass and its gram capacity. The gram capacity here is calculated according to the number of active lithium ions actually removed by each lithium replenisher when replenishing lithium, which is well known in the industry. For example, for Li5FeO4, its gram capacity corresponds to its theoretical gram capacity for releasing 4 lithium ions; for Li6CoO4, its gram capacity corresponds to its theoretical gram capacity for releasing 5 lithium ions; for Li2CuO2, its gram capacity corresponds to its theoretical gram capacity for releasing 1 lithium ion; for Li2CO3, its gram capacity corresponds to its theoretical gram capacity for releasing 2 lithium ions; for Li2C2O4, its gram capacity corresponds to its theoretical gram capacity for releasing 2 lithium ions; for Li3N, its gram capacity corresponds to its theoretical gram capacity for releasing 3 lithium ions.

[0032] In the present application, when the positive electrode material layer 30 is a single layer (eg Figure 1 As shown), the second positive electrode lithium supplement 301 is uniformly dispersed in the positive electrode active material 302. In some embodiments of the present application, the positive electrode material layer 30 is multi-layered, which includes n layers of positive electrode material sub-layers, n ≥ 2 (such as Figure 2 As shown). In the direction from the positive electrode current collector 10 to the lithium supplement layer 20 (that is, the direction from the positive electrode current collector 10 to the positive electrode material layer 30), Figure 2 ), the mass ratio of the second positive electrode lithium replenisher 301 to the positive electrode active material 302 in each positive electrode sub-coating layer tends to increase.

[0033] The following is an explanation of the increasing trend of the above parameters. From the positive electrode current collector 10 to the lithium replenishing layer 20, each sub-coating of the positive electrode material layer 30 can be sequentially recorded as 31, 32...3n. In this way, the surface of the positive electrode current collector 10 is sequentially provided with a lithium replenishing layer 20, a first positive electrode material sub-layer 31, a second positive electrode material sub-layer 32, ..., and an nth positive electrode material sub-layer 3n. If the mass ratio of the second positive electrode lithium replenisher to the positive electrode active material in the first positive electrode material sub-layer 31 is recorded as X1, the mass ratio of the second positive electrode lithium replenisher to the positive electrode active material in the second positive electrode material sub-layer 32 is recorded as X2, ..., the mass ratio of the second positive electrode lithium replenisher to the positive electrode active material in the nth positive electrode material sub-layer 3n is recorded as X n , then the above “increasing trend” can be expressed as: X1≤X2≤X3…≤X n , and X n >X1, where X1 is greater than 0. For example, the above “increasing trend” may specifically be: first increase-then remain unchanged-then increase, or first remain unchanged and then increase sequentially, or first remain unchanged-then increase-then remain unchanged-then increase, or a non-sequential increase method such as increasing layer by layer (such as X1<X2<X3…<X n ).

[0034] The second positive electrode lithium replenisher decomposes at a voltage greater than its delithiation potential to produce active lithium ions to replenish the battery, while releasing gas, so after decomposition, pores can be left at its original position, increasing the porosity of each positive electrode material sublayer. The present application controls the mass ratio of the second positive electrode lithium replenisher to the positive electrode active material in each positive electrode material sublayer to increase in the direction away from the positive electrode current collector 10, which is more conducive to the smooth discharge of the gas generated by the decomposition of the second positive electrode lithium replenisher in each positive electrode material sublayer close to the positive electrode current collector, and the degree of battery polarization caused by the residual gas is reduced. At the same time, after the decomposition of this type of lithium replenisher, the pores created in each positive electrode material sublayer also constitute a gradient pore structure, that is, the number of pores in the positive electrode material sublayer close to the positive electrode current collector 10 is small and the porosity is small, and the porosity of the positive electrode material 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 and reduce its pore tortuosity, thereby reducing the overall impedance of the battery and improving the power performance of the battery.

[0035] In some embodiments of the present application, from the positive electrode current collector 10 to the lithium supplement layer 20 (that is, the direction from the positive electrode current collector 10 to the positive electrode material layer 30, Figure 2 In the direction indicated by the arrow in the figure), the mass ratio of the second positive electrode lithium supplement 301 to the positive electrode active material in each positive electrode sub-coating layer increases layer by layer. This is conducive to the smoother discharge of the gas generated during the decomposition process of the second positive electrode lithium supplement in the positive electrode material layer 30, and after its decomposition, the positive electrode material layer is given a pore structure with a porosity increasing in the direction of the arrow, which is more conducive to reducing the battery impedance.

[0036] In some embodiments of the present application, among the n layers of positive electrode material sub-layers, at least two adjacent layers satisfy: A m / (D m / D m-1 )-A m-1 ≥5%; among which, A m-1 is the mass ratio of the second positive electrode lithium replenisher in the m-1th positive electrode material sublayer to the total second positive electrode lithium replenisher in the positive electrode material layer, A m is the mass ratio of the second positive electrode lithium replenisher in the mth positive electrode material sublayer to the total second positive electrode lithium replenisher in the positive electrode material layer, D m-1 is the thickness of the m-1th positive electrode material sublayer, D m is the thickness of the mth positive electrode material sublayer, m is any integer from 2 to n; on the same side of the positive electrode current collector, the m-1th positive electrode material sublayer is closer to the positive electrode current collector than the mth positive electrode material sublayer. That is to say, when the thickness of each positive electrode material sublayer is roughly the same, at least two adjacent layers of the 1st to nth positive electrode material 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 supplement is decomposed, the porosity of at least two adjacent positive electrode material sublayers can be clearly distinguished, and the above-mentioned gradient pore structure has a better effect of reducing battery impedance and improving power performance. In some embodiments of the present application, among the n layers of positive electrode material sublayers, any two adjacent layers of positive electrode material 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-1 ≥10%, for example, 10%, 15%, 20%, 25%, 30%, 40%, 50%, or 60%, etc.

[0037] For example, in some embodiments, when the thickness of each cathode material sublayer is substantially the same (ie, D m / D m-1 =1), the difference in mass proportion between the second positive electrode lithium replenisher in any two adjacent positive electrode material sub-layers and the total mass of the second positive electrode lithium replenisher in the positive electrode material layer 30 is greater than 5%. m / D m-1 = 1, among the n layers of positive electrode material sub-layers, any two adjacent layers of positive electrode material sub-layers satisfy: A m -A m-1≥5%, m is any integer from 2 to n. If the mass ratio of the second positive electrode lithium replenisher in the first positive electrode material sublayer 31 to the total mass ratio of the second positive electrode lithium replenisher in the positive electrode material layer 30 is recorded as A1, the mass ratio of the second positive electrode lithium replenisher in the second positive electrode material sublayer 32 to the total mass ratio of the second positive electrode lithium replenisher in the positive electrode material layer 30 is recorded as A2, ..., the mass ratio of the second positive electrode lithium replenisher in the nth positive electrode material sublayer 3n to the total mass ratio of the second positive electrode lithium replenisher in the positive electrode material layer 30 is recorded as A n , if D m / D m-1 =1, then |A2-A1|, |A3-A2|, ... |A n -A n-1 |are all ≥5%, preferably ≥10%. Wherein, A1 is greater than 0. 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%.

[0038] In the embodiment of the present application, the mass proportion of the positive electrode active material in each positive electrode material sublayer is more than 80%, preferably more than 90%. This is more conducive to ensuring that the reversible capacity provided by each positive electrode material sublayer is high, thereby ensuring that the reversible capacity of the overall positive electrode is high. Among them, taking the first positive electrode material sublayer 31 as an example, specifically, the ratio of the mass of the positive electrode active material in the first positive electrode material sublayer 31 to the total mass of the first positive electrode material sublayer 31 is more than 80%, and further more than 90%.

[0039] In the present application, the single-sided surface density of each positive electrode material sub-layer may be equal or unequal; in some embodiments of the present application, the single-sided surface density of each positive electrode material sub-layer is equal. This helps to ensure that their stacked structure is more stable. It should be noted that the single-sided surface density mentioned here and the single-sided surface density of the positive electrode material layer 30 and the lithium supplement layer 20 mentioned in the previous text of this application all refer to the single-sided surface density of each positive electrode material sub-layer before the battery is cycled for the first time (i.e., before formation).

[0040] 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 stacked structure (such as a lithium supplement layer 20 and a positive electrode material layer 30) may be formed on one side of the positive electrode current collector 10. Figure 1 and Figure 2As shown in FIG. 1 , a stacked structure in which the lithium supplement layer 20 and the positive electrode material layer 30 are formed on both sides of the positive electrode current collector 10 may also be formed.

[0041] In the present application, the lithium supplement layer 20 may also contain a conductive agent; the positive electrode material layer 30 may also contain a conductive agent. Each conductive agent 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, graphene, carbon fiber, etc. Among them, the carbon nanotubes may be specifically single-walled carbon nanotubes or multi-walled carbon nanotubes, and the carbon fiber may be specifically arrayed carbon fiber. In some embodiments, the lithium supplement layer 20 and the positive electrode material layer 30 may also contain one or more of a binder and a dispersant. Among them, each binder 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, etc., but is not limited thereto. Each dispersant may be selected from one or more of polyvinyl pyrrolidone (PVP), polyvinyl alcohol (PVA), etc.

[0042] Among them, the lithium replenishing layer 20 can be formed by coating and drying a primer slurry containing a first positive electrode lithium replenishing agent, a conductive agent, 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 positive electrode material layer 30 can be formed by coating and drying a positive electrode slurry containing a positive electrode active material, a second positive electrode lithium replenishing agent, a conductive agent, and a solvent. Among them, when the positive electrode material layer 30 is a layer, the positive electrode slurry is one type, and when the positive electrode material layer 30 is a multi-layer, the type of positive electrode slurry used corresponds to the number of layers of the positive electrode material layer 30.

[0043] 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 1-50%. The solid content of the positive electrode slurry is in the range of 50%-70%.

[0044] In addition, each slurry can be applied simultaneously or sequentially in a stacked manner, or applied on the coating formed by drying the previous slurry. Taking the case of a positive electrode material layer 30 as an example, a positive electrode slurry can be directly applied on the primer 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, the above primer slurry can be applied on one side surface of the positive electrode current collector 10 and dried to form a lithium replenishing layer 20, and then the positive electrode slurry can be applied on the lithium replenishing layer 20, and dried to form a positive electrode material layer 30, and then rolled.

[0045] The present application also provides a lithium battery, which includes the positive electrode 100 of the present application. Due to the use of the positive electrode 100, the utilization rate of the two types of lithium supplements in the lithium battery is high, the reversible capacity of the battery is high, the energy density is improved, and the battery impedance is low and the power performance is good.

[0046] In the embodiment of the present application, the lithium battery further includes a negative electrode, and a separator and an electrolyte disposed between the positive electrode and the negative electrode.

[0047] Among them, the negative electrode 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.

[0048] The diaphragm is used to separate the positive electrode and the negative electrode to maintain the insulation and liquid retention characteristics between the two; the diaphragm, the positive electrode and the negative electrode 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, the diaphragm and the negative electrode 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.

[0049] 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.

[0050] The present application also provides a device, which includes the lithium battery of the present application. The device can be a vehicle (such as a car, motorcycle, bicycle, etc.), an electric toy, a 3C product (such as a mobile phone, a laptop, a tablet computer, a pen-type computer, an e-book player, a wearable device, etc.) or an energy storage system. The electric device powered by the lithium battery has a long operating time and a fast charging speed.

[0051] The technical solution of the present application is further described below in conjunction with a number of specific embodiments.

[0052] Example 1

[0053] A method for preparing a positive electrode, comprising:

[0054] The first positive electrode lithium supplement agent (specifically Li5FeO4 with a carbon coating layer on the surface, the coating material accounts for 3wt%), the binder PVDF, the conductive agent carbon black, the dispersant PVP, and the solvent NMP are mixed in a mass ratio of 10:1:1:0.1:90, and stirred evenly to obtain a primer slurry, which is sprayed on the surface of the positive electrode current collector-aluminum foil, and then dried to form an aluminum foil with a lithium supplement layer; wherein the single-sided surface density of the lithium supplement layer is 2.41g / m 2 , the coating thickness is 3±1μm.

[0055] The positive electrode active material - lithium iron phosphate (LFP, Dv50 is 3μm) is mixed evenly with a binder PVDF, a carbon nanotube conductive agent, a graphene conductive agent, a second positive electrode lithium supplement agent (specifically Li2CO3 with a Dv50 of 200nm), and a solvent NMP in a mass ratio of 100:2.5:1:0.5:1:60 to prepare a positive electrode slurry; the positive electrode slurry is coated on the above-mentioned lithium supplement layer, and dried to form a single-sided surface density of 200g / m 2 positive electrode material layer.

[0056] Repeat the above steps of forming the lithium replenishing layer and the positive electrode material layer on the other side of the aluminum foil, and then roll-press to obtain a positive electrode to be used. In the positive electrode, the ratio of the lithium replenishing capacity of the first positive electrode lithium replenishing agent to that of the second positive electrode lithium replenishing agent is about 1:1.

[0057] Preparation of a lithium battery:

[0058] (1) Preparation of negative electrode: 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 coated on the negative electrode current collector - copper foil, and after drying, a single-sided surface density of 100g / m 2 negative electrode material layer.

[0059] (2) Battery assembly: The positive electrode and the separator (specifically, a PP separator with a thickness of 14 μm) and the negative electrode 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 drying, the prepared electrolyte is injected, and the battery casing is sealed and an air bag is reserved to obtain a lithium battery for subsequent electrical performance testing.

[0060] Example 2

[0061] A preparation of a positive electrode, which differs from Example 1 in that: the positive electrode material layer is two layers, and the first positive electrode slurry and the second positive electrode slurry are laminated and coated on one side of the lithium replenishing layer at the same time, and after drying, the first positive electrode slurry forms a first positive electrode material sublayer, and the second positive electrode slurry forms a second positive electrode material sublayer, the first positive electrode material sublayer is close to the lithium replenishing layer, and the second positive electrode material sublayer is arranged on the side of the first positive electrode material sublayer away from the lithium replenishing layer; wherein the formula of the first positive electrode slurry in contact with the lithium replenishing layer is lithium iron phosphate: P VDF: carbon nanotubes: graphene: Li2CO3: NMP = 100: 2.6: 1: 0.5: 0.5: 60. The formula of the second positive electrode slurry away from the lithium supplement layer is lithium iron phosphate: PVDF: carbon nanotubes: graphene: Li2CO3: NMP = 100: 2.4: 1: 0.5: 1.5: 60. The surface density ratio of the first positive electrode material sublayer and the second positive electrode material sublayer is 1: 1. The single-sided surface density of the total positive electrode material layer is still 200g / m 2 In the positive electrode, the ratio of the lithium replenishing capacity of the first positive electrode lithium replenishing agent to that of the second positive electrode lithium replenishing agent is still 1:1.

[0062] According to the method described in Example 1, the positive electrode of Example 2 is assembled into a lithium battery.

[0063] Example 3

[0064] A method for preparing a positive electrode, comprising:

[0065] The first positive electrode lithium supplement agent (specifically Li6CoO4 with a carbon coating layer on the surface, the coating material accounts for 2.5wt%), the binder PVDF, the conductive agent carbon black, PVP, and NMP are mixed in a mass ratio of 10:1:1:0.2:90, and stirred evenly to obtain a primer slurry, which is sprayed on the surface of the aluminum foil, and after drying, an aluminum foil current collector with a lithium supplement layer is formed; wherein the single-sided surface density of the lithium supplement layer is 2.46g / m 2 , thickness is 3±1μm.

[0066] The positive electrode active material lithium iron phosphate (LFP, Dv50 is 3 μm) is mixed evenly with the binder PVDF, carbon nanotubes, graphene, the second positive electrode lithium supplement (specifically Li2C2O4 with Dv50 of 150 nm), and the solvent NMP in a mass ratio of 100:2.5:1:0.5:1.4:60 to prepare a positive electrode slurry; the positive electrode slurry is coated on the above-mentioned lithium supplement layer, and after drying, a single-sided surface density of 200 g / m 2 The total mass of the second positive electrode lithium supplement in the positive electrode material layer is 1.4% of the total mass of the positive electrode active material.

[0067] Repeat the above steps of forming the lithium replenishing layer and the positive electrode material layer on the other side of the aluminum foil, and then roll-press to obtain a positive electrode to be used. In this positive electrode, the ratio of the lithium replenishing capacity of the first positive electrode lithium replenishing agent to that of the second positive electrode lithium replenishing agent is 1.2:1.

[0068] According to the method described in Example 1, the positive electrode of Example 3 was assembled into a lithium battery.

[0069] Example 4

[0070] A preparation of a positive electrode, which differs from Example 3 in that: the positive electrode material layer is two layers, double-layer coating is adopted, and the first positive electrode slurry and the second positive electrode slurry are laminated and coated on one side of the lithium replenishing layer at the same time, and after drying, the first positive electrode slurry forms a first positive electrode material sublayer, and the second positive electrode slurry forms a second positive electrode material sublayer, the first positive electrode material sublayer is close to the lithium replenishing layer, and the second positive electrode material sublayer is arranged on the side of the first positive electrode material sublayer away from the lithium replenishing layer; the formula of the first positive electrode slurry in contact with the lithium replenishing layer is lithium iron phosphate: P VDF: carbon nanotubes: graphene: Li2C2O4: NMP = 100: 2.6: 1: 0.5: 0.7: 60. The formula of the second positive electrode slurry away from the lithium supplement layer is lithium iron phosphate: PVDF: carbon nanotubes: graphene: Li2C2O4: NMP = 100: 2.4: 1: 0.5: 2.1: 60. The surface density ratio of the first positive electrode material sublayer and the second positive electrode material sublayer is controlled to be 1: 1. The single surface density of the total positive electrode material layer is still 200g / m 2 In the positive electrode, the ratio of the lithium replenishing capacity of the first positive electrode lithium replenishing agent to that of the second positive electrode lithium replenishing agent is still 1.2:1.

[0071] According to the method described in Example 1, the negative electrode of Example 4 was assembled into a lithium battery.

[0072] Example 5

[0073] A method for preparing a positive electrode, comprising:

[0074] The first positive electrode lithium supplement agent (specifically Li2CuO2 without a coating layer) is mixed with a binder PVDF, a conductive agent carbon black, PVP, and NMP in a mass ratio of 10:1:1:0.2:90, and stirred evenly to obtain a primer slurry, which is sprayed on the surface of an aluminum foil, and dried to form an aluminum foil current collector with a lithium supplement layer; wherein the single-sided surface density of the lithium supplement layer is 4g / m 2 , the coating thickness is 5±1μm.

[0075] The positive electrode active material lithium iron phosphate (LFP, Dv50 is 3μm) is mixed with the binder PVDF, carbon nanotubes, graphene, the second positive electrode lithium supplement (specifically Li3N with Dv50 of 400nm), and the solvent NMP at a mass ratio of 100:2.5:1:0.5:1:60 to prepare a positive electrode slurry. The positive electrode slurry is coated on the above-mentioned lithium supplement layer and dried to form a single-sided surface density of 200g / m 2 positive electrode material layer.

[0076] Repeat the above steps of forming the lithium supplement layer and the positive electrode material layer on the other side of the aluminum foil, and then roll-press to obtain a positive electrode to be used. According to the method described in Example 1, the positive electrode of Example 5 was assembled into a lithium battery.

[0077] Example 6

[0078] A preparation of a positive electrode, which differs from Example 5 in that: the positive electrode material layer is two layers, double-layer coating is adopted, and the first positive electrode slurry and the second positive electrode slurry are laminated and coated on one side of the lithium replenishing layer at the same time, and after drying, the first positive electrode slurry forms a first positive electrode material sublayer, and the second positive electrode slurry forms a second positive electrode material sublayer, the first positive electrode material sublayer is close to the lithium replenishing layer, and the second positive electrode material sublayer is arranged on the side of the first positive electrode material sublayer away from the lithium replenishing layer; wherein the formula of the first positive electrode slurry in contact with the lithium replenishing layer is Lithium iron phosphate: PVDF: carbon nanotubes: graphene: Li3N: NMP = 100: 2.6: 1: 0.5: 0.4: 60. The formula of the second positive electrode slurry away from the lithium supplement layer is lithium iron phosphate: PVDF: carbon nanotubes: graphene: Li3N: NMP = 100: 2.4: 1: 0.5: 1.6: 60. The surface density ratio of the first positive electrode material sublayer and the second positive electrode material sublayer is 1: 1. The single-sided surface density of the total positive electrode material layer is still 200g / m 2 .

[0079] According to the method described in Example 1, the positive electrode of Example 6 was assembled into a lithium battery.

[0080] Example 7

[0081] The difference between Example 7 and Example 1 is that the first positive electrode lithium supplement is Li5FeO4 without a conductive coating layer on the surface.

[0082] Example 8

[0083] The main difference between the positive electrode of Example 8 and Example 1 is that the lithium supplement layer also contains positive electrode active material LFP.

[0084] The lithium replenishing layer is obtained by coating and drying the primer slurry obtained by mixing the first positive electrode lithium replenishing agent with lithium iron phosphate (LFP, Dv50 is 3μm), binder PVDF, conductive agent carbon black, dispersant PVP, and solvent NMP in a mass ratio of 6:4:1:1:0.1:90. The single-sided surface density of the lithium replenishing layer is 3.97g / m 2 , thickness is 4±1μm.

[0085] The positive electrode slurry with the same formulation as in Example 1 is coated on the above lithium supplement layer and dried to form a single-sided surface density of 198 g / m 2 positive electrode material layer.

[0086] The above-mentioned operation of forming the lithium supplement layer and the positive electrode material layer is repeated on the other side of the aluminum foil, and then roll-pressing is performed to obtain the positive electrode.

[0087] In the positive electrode of Example 8, the ratio of the lithium replenishing capacity of the first positive electrode lithium replenishing agent to that of the second positive electrode lithium replenishing agent is still 1:1.

[0088] Example 9

[0089] The main difference between Example 9 and Example 1 is that in the positive electrode of Example 9, the ratio of the lithium replenishing capacity of the first positive electrode lithium replenishing agent to that of the second positive electrode lithium replenishing agent is 0.1:1. The formula composition of the primer slurry used to form the lithium replenishing layer in Example 9 is the same as that in Example 1, but the single-surface density of the lithium replenishing layer is 0.48 g / m 2 , the coating thickness is 2±1μm.

[0090] The positive electrode active material lithium iron phosphate (LFP, Dv50 is 3 μm) is mixed evenly with the binder PVDF, the carbon nanotube conductive agent, the graphene conductive agent, the second positive electrode lithium supplement agent (Li2CO3 with Dv50 of 200 nm), and the solvent NMP in a mass ratio of 100:2.5:1:0.5:2:60 to prepare a positive electrode slurry; the positive electrode slurry is coated on the above-mentioned lithium supplement layer, and dried to form a single-sided surface density of 200 g / m 2The total mass of the second positive electrode lithium supplement in the positive electrode material layer is 2% of the total mass of the positive electrode active material.

[0091] Repeat the above steps of forming the lithium replenishing layer and the positive electrode material layer on the other side of the aluminum foil, and then roll-press to obtain a positive electrode to be used. In the positive electrode prepared in Example 9, the ratio of the lithium replenishing capacity of the first positive electrode lithium replenishing agent to that of the second positive electrode lithium replenishing agent is 0.1:1.

[0092] Example 10

[0093] The main difference between Example 10 and Example 1 is that the ratio of the lithium replenishing capacity of the first positive electrode lithium replenishing agent to the second positive electrode lithium replenishing agent in Example 10 is 9:1. The formula composition of the primer slurry used to form the lithium replenishing layer in Example 10 is the same as that in Example 1, but the single-surface density of the lithium replenishing layer is 4.38 g / m 2 , the coating thickness is 5±1μm.

[0094] The positive electrode active material lithium iron phosphate (LFP, Dv50 is 3 μm) is mixed evenly with the binder PVDF, the carbon nanotube conductive agent, the graphene conductive agent, the second positive electrode lithium supplement agent (Li2CO3 with Dv50 of 200 nm), and the solvent NMP in a mass ratio of 100:2.5:1:0.5:0.2:60 to prepare a positive electrode slurry; the positive electrode slurry is coated on the above-mentioned lithium supplement layer, and dried to form a single-sided surface density of 200 g / m 2 The total mass of the second positive electrode lithium supplement in the positive electrode material layer is 0.2% of the total mass of the positive electrode active material.

[0095] Repeat the above steps of forming the lithium replenishing layer and the positive electrode material layer on the other side of the aluminum foil, and then roll-press to obtain a positive electrode to be used. In the positive electrode of Example 10, the ratio of the lithium replenishing capacity of the first positive electrode lithium replenishing agent to the second positive electrode lithium replenishing agent is 9:1; the total mass of the second positive electrode lithium replenishing agent is 0.2% of the total mass of the positive electrode active material.

[0096] Embodiment 11

[0097] The main difference between Example 11 and Example 1 is that the Dv50 of the second positive electrode lithium supplement is 600nm.

[0098] Example 12

[0099] The main difference between Example 12 and Example 1 is that the Dv50 of the second positive electrode lithium supplement is 20 nm, and the Dv50 of the positive electrode active material - lithium iron phosphate (LFP) is 0.2 μm.

[0100] Embodiment 13

[0101] The main difference between Example 13 and Example 1 is that the Dv50 of the second positive electrode lithium supplement is 500nm, and the Dv50 of the positive electrode active material - lithium iron phosphate (LFP) is 5μm.

[0102] Embodiment 14

[0103] The main difference between the positive electrode of Example 14 and Example 1 is that in the positive electrode of Example 14, the total mass of the second positive electrode lithium replenisher is 0.5% of the total mass of the positive electrode active material; the ratio of the lithium replenishing capacity of the first positive electrode lithium replenisher to the second positive electrode lithium replenisher is about 3:1. Among them, the single-sided surface density of the lithium replenishing layer is 3.65g / m 2 , the single-side thickness is 4±1μm.

[0104] The positive electrode active material - lithium iron phosphate (LFP, Dv50 is 3μm) is mixed evenly with a binder PVDF, a carbon nanotube conductive agent, a graphene conductive agent, a second positive electrode lithium supplement agent (specifically Li2CO3 with a Dv50 of 200nm), and a solvent NMP in a mass ratio of 100:2.5:1:0.5:0.5:60 to prepare a positive electrode slurry; the positive electrode slurry is coated on the above-mentioned lithium supplement layer, and dried to form a single-sided surface density of 200g / m 2 The total mass of the second positive electrode lithium supplement in the positive electrode material layer is 0.5% of the total mass of the positive electrode active material.

[0105] Repeat the above steps of forming the lithium supplement layer and the positive electrode material layer on the other side of the aluminum foil, and then roll-press to obtain a positive electrode to be used. According to the method described in Example 1, the positive electrode of Example 14 was assembled into a lithium battery.

[0106] Embodiment 15

[0107] The main difference between Example 15 and Example 1 is that in the positive electrode of Example 15, the total mass of the second positive electrode lithium replenisher is 5% of the total mass of the positive electrode active material; the ratio of the lithium replenishing capacity of the first positive electrode lithium replenisher to the second positive electrode lithium replenisher is about 0.15:1. The single surface density of the lithium replenishing layer is 1.74g / m 2 , the single-side thickness is 2±1μm.

[0108] The positive electrode active material - lithium iron phosphate (LFP, Dv50 is 3μm) is mixed evenly with a binder PVDF, a carbon nanotube conductive agent, a graphene conductive agent, a second positive electrode lithium supplement agent (specifically Li2CO3 with a Dv50 of 200nm), and a solvent NMP in a mass ratio of 100:2.5:1:0.5:5:60 to prepare a positive electrode slurry; the positive electrode slurry is coated on the above-mentioned lithium supplement layer, and dried to form a single-sided surface density of 200g / m 2 The total mass of the second positive electrode lithium supplement in the positive electrode material layer is 5% of the total mass of the positive electrode active material.

[0109] Repeat the above steps of forming the lithium supplement layer and the positive electrode material layer on the other side of the aluminum foil, and then roll-press to obtain a positive electrode to be used. According to the method described in Example 1, the positive electrode of Example 15 was assembled into a lithium battery.

[0110] Example 16

[0111] The main difference between the positive electrode of Example 16 and Example 1 is that the lithium supplement layer also contains positive electrode active material (specifically LFP, Dv50 is 3 μm), and the single-sided surface density of the lithium supplement layer is 20 g / m 2 The single-sided thickness is 12±1μm. The lithium supplement layer is obtained by coating and drying the primer slurry obtained by mixing the first positive electrode lithium supplement agent with LFP, binder PVDF, conductive agent carbon black, dispersant PVP, and solvent NMP in a mass ratio of 2:8:0.2:0.2:0.1:90. In addition, the single-sided surface density of the positive electrode material layer is 180g / m 2 .

[0112] Correspondingly, in the positive electrode of Example 16, the ratio of the lithium replenishing capacity of the first positive electrode lithium replenishing agent to that of the second positive electrode lithium replenishing agent is approximately 2.12:1.

[0113] Embodiment 17

[0114] The main difference between the positive electrode of Example 17 and Example 1 is that the single-sided surface density of the lithium supplement layer is 50 g / m 2 The single-sided thickness is 30±1μm. The lithium supplement layer is obtained by coating and drying the primer slurry obtained by mixing the first positive electrode lithium supplement agent with LFP, binder PVDF, conductive agent carbon black, dispersant PVP, and solvent NMP in a mass ratio of 0.8:9.2:0.2:0.2:0.1:90. In addition, the single-sided surface density of the positive electrode material layer is 150g / m 2 .

[0115] In the positive electrode of Example 17, the ratio of the lithium replenishing capacity of the first positive electrode lithium replenishing agent to that of the second positive electrode lithium replenishing agent is approximately 2.55:1.

[0116] Embodiment 18

[0117] The main difference between Example 18 and Example 1 is that in the positive electrode of Example 18, the ratio of the lithium replenishing capacity of the first positive electrode lithium replenishing agent to that of the second positive electrode lithium replenishing agent is about 2:1; wherein the single surface density of the lithium replenishing layer is 4.81 g / m 2 , single-side thickness is 5±1μm.

[0118] Embodiment 19

[0119] The main difference between Example 19 and Example 2 in the preparation method is that the formula of the first positive electrode slurry in contact with the lithium replenishing layer is lithium iron phosphate: PVDF: carbon nanotubes: graphene: Li2CO3: NMP = 100: 2.6: 1: 0.5: 0.9: 60, and the formula of the second positive electrode slurry away from the lithium replenishing layer is lithium iron phosphate: PVDF: carbon nanotubes: graphene: Li2CO3: NMP = 100: 2.4: 1: 0.5: 1.1: 60.

[0120] In Example 19, the mass ratio of the second positive electrode lithium replenisher in the first positive electrode material sublayer formed by drying the first positive electrode slurry to the total second positive electrode lithium replenisher in the positive electrode is 45%, and the mass ratio of the second positive electrode lithium replenisher in the second positive electrode material sublayer formed by drying the second positive electrode slurry to the total second positive electrode lithium replenisher in the positive electrode is 55%. In addition, the surface density ratio of the first positive electrode material sublayer and the second positive electrode material sublayer is still 1:1, and the single-sided surface density of the total positive electrode material layer is still 200g / m 2 ; In this positive electrode, the ratio of the lithium replenishing capacity of the first positive electrode lithium replenishing agent to that of the second positive electrode lithium replenishing agent is still 1:1.

[0121] Embodiment 20

[0122] A positive electrode, which is different from the positive electrode of Example 1 only in that the positive electrode active material is lithium manganese iron phosphate (LMFP) with a Dv50 of 1 μm.

[0123] Preparation of a lithium battery:

[0124] (1) Preparation of negative electrode: The negative electrode active material graphite, silicon-carbon composite material, binder SBR, thickener CMC, conductive agent carbon black and solvent H2O are mixed evenly in a mass ratio of 90:10:2:2:1:120 to prepare a negative electrode slurry. The negative electrode slurry is applied to the negative electrode current collector - copper foil, and after drying, a single-sided surface density of 80 g / m 2 of the negative electrode material layer.

[0125] (2) Battery assembly: The positive electrode and the separator (specifically, a PP separator with a thickness of 14 μm) and the negative electrode 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 drying, the prepared electrolyte is injected, and the battery casing is sealed and an air bag is reserved to obtain a lithium battery for subsequent electrical performance testing.

[0126] In order to highlight the beneficial effects of the present application, the present application also provides the following comparative examples 1-8.

[0127] Comparative Example 1

[0128] A preparation of a positive electrode, which is different from Example 1 in that the positive electrode does not contain the first and second types of positive electrode lithium replenishers.

[0129] The preparation method of the positive electrode comprises: mixing lithium 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.

[0130] According to the method described in Example 1, the positive electrode of Comparative Example 1 was assembled into a lithium battery.

[0131] Comparative Example 2

[0132] The difference between the positive electrode of Comparative Example 2 and Example 7 is that a mixed layer containing the first positive electrode lithium replenisher and the positive electrode active material is directly disposed on the aluminum foil.

[0133] The preparation of the positive electrode in comparative example 2 specifically includes: mixing lithium iron phosphate, binder PVDF, carbon nanotube conductive agent, graphene conductive agent, first positive electrode lithium supplement agent (specifically Li5FeO4 without carbon coating layer on the surface, the coating layer material accounts for 3wt%), and solvent NMP in a mass ratio of 100:2.5:1:0.5:2:60 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 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.

[0134] According to the method described in Example 1, the positive electrode of Comparative Example 2 was assembled into a lithium battery.

[0135] Comparative Example 3

[0136] A positive electrode, which is different from Example 3 mainly in that a mixed layer containing a second positive electrode lithium replenisher and a positive electrode active material is directly arranged on the aluminum foil.

[0137] The preparation of the positive electrode in Comparative Example 3 specifically includes: mixing lithium iron phosphate, binder PVDF, carbon nanotubes, graphene, the second positive electrode lithium supplement Li2C2O4, and solvent NMP in a mass ratio of 100:2.5:1:0.5:3:60 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 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.

[0138] According to the method described in Example 1, the positive electrode of Comparative Example 3 was assembled into a lithium battery.

[0139] Comparative Example 4

[0140] A positive electrode, which is different from Example 1 mainly in that: a positive electrode material layer without a lithium replenisher is arranged on an aluminum foil, and a second lithium replenisher layer containing a second positive electrode lithium replenisher is arranged on the positive electrode active material layer.

[0141] The slurry formula for forming the positive electrode material layer does not contain the second positive electrode lithium supplement, and the relative contents of other substances are the same as those in Example 1. The single-surface density of the positive electrode material layer is still 200 g / m 2 The slurry for forming the second lithium replenishing layer is obtained by mixing the second positive electrode lithium replenishing agent with the binder PVDF, the conductive agent carbon black, the dispersant PVP, and the solvent NMP in a mass ratio of 10:1:1:0.1:90; the single surface density of the second lithium replenishing layer is 4.6g / m 2 .

[0142] According to the method described in Example 1, the positive electrode of Comparative Example 4 was assembled into a lithium battery.

[0143] Comparative Example 5

[0144] A positive electrode, which is different from Example 1 in that: the positive electrode material layer containing the second positive electrode lithium replenisher in Example 1 is directly in contact with the aluminum foil, and the lithium replenishing layer in Example 1 is arranged on the side of the positive electrode material layer away from the aluminum foil.

[0145] According to the method described in Example 1, the positive electrode of Comparative Example 5 was assembled into a lithium battery.

[0146] Comparative Example 6

[0147] A positive electrode, which is mainly different from Example 4 in that: there is no lithium supplement layer on the aluminum foil current collector, but a first positive electrode material sublayer and a second positive electrode material sublayer are directly stacked in sequence. Among them, in Comparative Example 6, the first positive electrode slurry formula for forming the first positive electrode material sublayer close to the current collector is lithium iron phosphate: PVDF: carbon nanotubes: graphene: Li2C2O4: NMP = 100: 2.6: 1: 0.5: 1.5: 60, and the second positive electrode slurry formula for forming the second positive electrode material sublayer away from the current collector is lithium iron phosphate: PVDF: carbon nanotubes: graphene: Li2C2O4: NMP = 100: 2.4: 1: 0.5: 4.6: 60, and the surface density ratio of the first positive electrode material sublayer formed by drying the first positive electrode slurry and the second positive electrode material sublayer formed by drying the second positive electrode slurry is controlled to be 1: 1, and the single-sided surface density of the total positive electrode material layer is still 200g / m 2 .

[0148] According to the method described in Example 1, the positive electrode of Comparative Example 6 was assembled into a lithium battery.

[0149] Comparative Example 7

[0150] 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.

[0151] 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.

[0152] According to the method described in Example 1, the positive electrode of Comparative Example 7 was assembled into a lithium battery.

[0153] Comparative Example 8

[0154] A positive electrode, which is different from Example 7 in that: a lithium replenishing layer is arranged on the aluminum foil, and a positive electrode material layer not containing a second positive electrode lithium replenishing agent is arranged on the lithium replenishing layer.

[0155] The slurry formula for forming the lithium supplement layer is the same as that in Example 7, and the single-sided surface density of the lithium supplement layer is 4.82 g / m 2 , thickness is 5±1μm; the slurry forming the positive electrode material layer is a positive electrode active material lithium iron phosphate (LFP, Dv50 is 3μm) and a binder PVDF, a carbon nanotube conductive agent, a graphene conductive agent, and a solvent NMP mixed in a mass ratio of 100:2.5:1:0.5:60. The single-sided surface density of the positive electrode material layer is 200g / m 2 .

[0156] In order to strongly support the beneficial effects brought by the technical solution of the present application, the lithium batteries of the above embodiments or comparative examples were subjected to the following performance tests:

[0157] a. Positive electrode gram capacity test: At room temperature (25°C), 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 at formation). After aging (aging procedure is 100% SOC state and storage at 45°C for 48h, the same below), discharge at 1 / 3C to a lower limit voltage of 2.0V, and calculate the first discharge capacity. Then the positive electrode gram capacity = first discharge capacity / mass of positive electrode active material. The first coulomb efficiency η = first discharge capacity / first charge capacity.

[0158] b. Cycle performance test: At room temperature (25°C), charge the aged batteries 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.

[0159] c. Battery DCIR test: At room temperature (25°C), charge each aged battery 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 at 25°C to 50% SOC, 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.

[0160] d. Utilization rate test of lithium supplement materials:

[0161] Make non-lithium-supplemented batteries corresponding to the lithium-supplemented batteries of the embodiments and comparative examples of the present application: wherein, embodiments 1-20 and comparative examples 2-6 and 8 are all lithium-supplemented batteries, comparative example 1 is the non-lithium-supplemented battery corresponding to embodiments 1-19 and comparative examples 2-6, and comparative example 7 is the non-lithium-supplemented battery corresponding to embodiment 20). At room temperature (25°C), the above batteries are charged to an upper limit voltage of 4.6V at a constant current and constant voltage of 1 / 3C for formation, and discharged to a lower limit voltage of 2.0V at 1 / 3C after aging. The discharge capacity of each lithium-supplemented battery is recorded as C1, and the discharge capacity of the corresponding non-lithium-supplemented battery is recorded as C2. Then the utilization rate of the lithium-supplemented material = (C1-C2) / (mass of the lithium-supplemented material × gram capacity of the lithium-supplemented material). The gram capacity of the lithium-supplemented material here is calculated according to the number of active lithium ions actually removed when each lithium-supplementing agent known in the industry replenishes lithium.

[0162] The relevant test results are summarized in Table 1 below.

[0163] Table 1

[0164]

[0165]

[0166] It can be seen from Examples 1 and 7 and Comparative Examples 1-2 and 4-5 in Table 1 that when the positive electrode of the battery does not contain a lithium replenisher (Comparative Example 1), the positive electrode gram capacity and the first coulomb efficiency of the battery are both low, and the DCIR value is high. However, in Comparative Examples 2 and 4-5, where the positive electrode contains only one type of positive electrode lithium replenisher, or the positive electrode contains two types of positive electrode lithium replenishers but they are not distributed as in Example 1 of the present application (the sum of the lithium replenishment capacity provided by the lithium replenisher in the positive electrode is close to that of Examples 1 and 7), although the positive electrode gram capacity and the first coulomb efficiency of the battery can be improved to a certain extent, the effect of reducing the DCIR value of the battery is not obvious, and the DCIR value impedance of the battery is still high (which can reflect the poor power performance of the battery). In Example 1 of the present application, a lithium replenisher layer containing a first positive electrode lithium replenisher material is used as a bottom coating on the current collector, and a positive electrode material layer formed by distributing the second positive electrode lithium replenisher material in the positive electrode active material is arranged on the bottom coating, which can increase the positive electrode gram capacity and reduce the battery impedance. In addition, similar phenomena can also be seen from the comparison between Comparative Example 3 and Example 3, and the comparison between Comparative Example 6 and Example 4.

[0167] In addition, from the comparison between Example 1 and Examples 9, 10, and 14, it can be learned that when the sum of the lithium replenishing capacities provided by the lithium replenishing agents in the positive electrode is close, and the composition of the lithium replenishing layer and the single-surface surface density of the positive electrode material layer are the same, when the ratio of the lithium replenishing capacity of the first positive electrode lithium replenishing agent to the second positive electrode lithium replenishing agent is in the range of (0.2-2):1, it is more conducive to improving the comprehensive performance of the lithium battery, especially reducing the battery DCIR value and improving the utilization rate of the lithium replenishing agent.

[0168] From the comparison between Examples 1, 12, and 13 and Example 11, it is known that when the composition, thickness, surface density, etc. of each layer in the positive electrode are the same but the Dv50 of the second positive electrode lithium replenisher and / or the positive electrode active material is different, the Dv50 of the second positive electrode lithium replenisher is in the range of 20-500nm and the Dv50 of the positive electrode active material is in the range of 0.2-5μm, which is more conducive to increasing the gram capacity of the battery positive electrode, thereby increasing the energy density of the positive electrode, and reducing the battery DCIR value.

[0169] In addition, from the comparison between Example 1 and Example 7, it can be seen that when other parameters of the battery positive electrode are the same, when the surface of the first positive electrode lithium supplement agent has a conductive coating layer, it is more conducive to reducing the battery impedance and improving the utilization rate of the lithium supplement material. The comparison between Example 20 and Comparative Example 7 in which the positive electrode active material is changed also has similar phenomena as that between Example 1 and Comparative Example 1.

[0170] 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, characterized in that It includes a positive electrode current collector and a lithium replenishing layer and a positive electrode material layer stacked in sequence on at least one side of the positive electrode current collector, wherein the lithium replenishing layer contains a first positive electrode lithium replenishing agent, and the positive electrode material layer contains a positive electrode active material and a second positive electrode lithium replenishing agent, 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 generate gas.

2. The positive electrode according to claim 1, characterized in that The first positive electrode lithium supplement includes one or more of Li6CoO4, Li2MoO3, Li5FeO4, Li6MnO4, Li2NiO2, Li2CuO2, Li3PO4, Li4SiO4, Li2SiO3, Li3VO4, Li2VO3, Li5ReO6, Li2RuO3, Li2MnO3, Li2MoO3, Li2S, and LiF.

3. The positive electrode according to claim 1 or 2, characterized in that The surface of the first positive electrode lithium supplement agent has a conductive coating layer.

4. The positive electrode according to any one of claims 1 to 3, characterized in that The lithium replenishing layer contains the following components in percentage by mass: 50%-90% of the first positive electrode lithium replenishing agent, 0-40% of the second positive electrode active material, 0.5-10% of the binder, and 0.5-10% of the conductive agent.

5. The positive electrode according to any one of claims 1 to 4, characterized in that The second positive electrode lithium supplement includes one or more of Li2CO3, Li3N, Li2O2, Li2O, Li2C2O4, Li2C4O4, Li2C3O5, and Li2C4O6.

6. The positive electrode according to any one of claims 1 to 5, characterized in that In the positive electrode material layer, the Dv50 of the second positive electrode lithium supplement is 20-500nm, and the Dv50 of the positive electrode active material is 0.2-5μm.

7. The positive electrode according to any one of claims 1 to 6, characterized in that In the positive electrode material layer, the total mass of the second positive electrode lithium supplement is 0.5-5% of the total mass of the positive electrode active material.

8. The positive electrode according to any one of claims 1 to 7, characterized in that The ratio of the lithium replenishing capacity that can be provided by the first positive electrode lithium replenishing agent and the second positive electrode lithium replenishing agent is (0.2-2):

1.

9. The positive electrode according to any one of claims 1 to 8, characterized in that The single-surface surface density of the positive electrode material layer is greater than the single-surface surface density of the lithium supplement layer.

10. The positive electrode according to any one of claims 1 to 9, characterized in that The single surface density of the lithium supplement layer is 0.5-50g / m 2 .

11. The positive electrode according to claim 10, characterized in that The single surface density of the lithium supplement layer is 0.5-20 g / m 2 .

12. The positive electrode according to any one of claims 1 to 11, characterized in that The single-side thickness of the lithium supplement layer is 0.1-100 μm.

13. The positive electrode according to claim 12, characterized in that The single-side thickness of the lithium supplement layer is 0.5-10 μm.

14. The positive electrode according to any one of claims 1 to 13, characterized in that The positive electrode material layer includes n positive electrode material sublayers, n≥2, wherein the mass ratio of the second positive electrode lithium supplement to the positive electrode active material in each positive electrode material sublayer increases from the positive electrode current collector to the positive electrode material layer.

15. The positive electrode according to any one of claims 1 to 13, characterized in that The positive electrode material layer includes n positive electrode material sublayers, n≥2, wherein the mass ratio of the second positive electrode lithium supplement to the positive electrode active material in each positive electrode material sublayer increases layer by layer from the positive electrode current collector to the positive electrode material layer.

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

17. The positive electrode according to claim 16, characterized in that Among the n layers of positive electrode material sub-layers, any two adjacent layers of the positive electrode material sub-layers satisfy: A m / (D m / D m-1 )-A m-1 ≥5%.

18. The positive electrode according to any one of claims 15 to 17, characterized in that The mass proportion of the positive electrode active material in each positive electrode material sub-layer is greater than 80%.

19. A lithium battery, characterized in that: The method comprises the positive electrode as claimed in any one of claims 1 to 18.

20. A device comprising the lithium battery as claimed in claim 19, wherein the device is an electrical device or an energy storage system.

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