CN115939308A - Lithium-supplement positive pole piece, preparation method thereof and lithium ion battery - Google Patents

Abstract

The invention discloses a lithium supplement positive pole piece, a preparation method thereof and a lithium ion battery. In the invention, the single lithium supplement reagent layer is distributed in a direction vertical to the width direction of the current collector, so that the electronic conduction between the positive active material layer and the current collector is not influenced, and the transmission path of lithium ions is not deteriorated.

Description

A lithium-supplemented positive electrode sheet and preparation method thereof and lithium-ion battery

Technical Field

The invention belongs to the technical field of lithium ion batteries and relates to a lithium-supplemented positive electrode plate and a preparation method thereof and a lithium ion battery.

Background Art

In order to meet the needs of electric vehicles and large-scale energy storage, the next generation of power batteries need higher energy density, while the next generation of energy storage batteries have a higher cycle life. The current technology that can simultaneously improve battery energy density and cycle life is lithium supplementation technology.

Lithium replenishment technologies mainly include negative electrode electrochemical method, negative electrode chemical method and positive electrode pre-lithiation method.

The negative electrode electrochemical method mainly involves assembling a battery with a negative electrode, a lithium source, and an electrolyte before assembling the battery, charging the negative electrode, storing a certain amount of lithium ions in the negative electrode in advance, and then assembling the negative electrode with the corresponding positive electrode material into a full battery. This method involves the problem of disassembling the battery and then assembling it, which makes the entire operation complicated, the process cost high, and is not suitable for mass production.

At present, the method that has been studied the most is the negative electrode chemical method, which is to conduct an oxidation-reduction reaction between the negative electrode material and metallic lithium or other low-potential lithium-containing chemical reagents to make up for the loss of lithium. Because in the electrolyte environment, the potential difference between metallic lithium and the negative electrode material causes the lithium ion flow to move in a directional manner, and the lithium ions generated by the lithium foil are released into the electrolyte. In order to maintain charge conservation, the lithium ions in the electrolyte are embedded in the negative electrode or undergo an oxidation-reduction reaction with it, so that the negative electrode is pre-lithiated. Although this solution has a simple process and high lithium replenishment efficiency, the capacity of metallic lithium is very high, and due to technical limitations, the surface capacity of the supplemented lithium source far exceeds the actual required active lithium ion capacity. In addition, lithium foil and other low-potential lithium-containing reagents are highly active and easily react with water, air and other gases in the air. The safety hazard is very large and it is difficult to be compatible with existing assembly processes.

Recently, the positive electrode pre-lithiation method has attracted the attention of many researchers. It is to add positive electrode pre-lithiation reagents to positive electrode materials. During the first charge, the pre-lithiation reagents with high lithium ion content in the molecule irreversibly release active lithium ions to make up for the first irreversible lithium consumption of the negative electrode material, thereby improving the battery energy density. The positive electrode pre-lithiation reagents can be blended with positive electrode materials using existing production processes, and the lithium replenishment capacity can be accurately controlled according to the added content, with high safety. Because of its simple process and perfect compatibility with existing battery processes, it can effectively improve the energy density of the entire battery, and can also accurately control the capacity of pre-lithiation lithium ions, which is very conducive to large-scale commercial applications.

At present, the common scheme for positive electrode lithium replenishment is to blend the lithium replenishment agent with the positive electrode material in the batching homogenization stage, and use the excess lithium ions released by the lithium replenishment agent during the first charge to compensate for the active lithium ion consumption of the battery cell, thereby improving the energy density and cycle life of the battery cell. However, most positive electrode lithium replenishers have the problem of poor conductivity, such as Li ₂ S, Li ₂ O, Li ₂ O ₂ , LiF, Li ₅ FeO ₄ , and Li ₂ NiO ₂ , which must be combined with a higher proportion of conductive agents to effectively release the lithium ions they contain. Simply blending the positive electrode lithium replenishment agent with the positive electrode active material will result in the lithium ions released by the lithium replenishment agent for the first time being lower than the theoretical capacity; in addition, due to the low-conductivity substances remaining after the lithium replenishment agent is de-lithiated, the resistance of the positive electrode sheet increases, which deteriorates the performance of the gram capacity of the positive electrode active material itself, and finally makes the energy density of the battery cell unsatisfactory and deteriorates the cycle life of the battery cell. In addition, CN 107068972 A coats the lithium supplement material layer on the surface of the positive electrode material layer. Although the ratio of the positive electrode material, the lithium supplement material and the conductive agent can be adjusted respectively to improve the capacity of the lithium supplement agent, the lithium supplement material layer coated on the surface of the positive electrode material will hinder the conduction of lithium ions, increase the transmission distance of lithium ions from the positive electrode material to the negative electrode material, lead to concentration polarization during charging and discharging, and deteriorate the electrochemical performance of the battery cell; at the same time, CN109686947A directly sets the lithium supplement layer on the surface of the current collector, which can avoid the lithium supplement layer from deteriorating the lithium ion conduction, but because the commonly used inorganic lithium supplement material itself has poor conductivity, this will deteriorate the electronic conduction rate and increase the physical internal resistance of the battery, and both methods must be coated multiple times, increasing the process cost.

Summary of the invention

In view of the problems existing in the prior art, the present invention provides a lithium-supplemented positive electrode sheet and a preparation method thereof and a lithium-ion battery, wherein the positive electrode active material and the lithium supplement agent are separated and homogenized, and different conductive agent contents are matched according to their respective electronic conduction characteristics, and then the two slurries are coated on the positive electrode current collector at one time by extrusion coating; and the lithium supplement material is distributed longitudinally (perpendicular to the width direction of the current collector), which neither affects the electronic conduction of the positive electrode material layer nor deteriorates the transmission path of lithium ions. At the same time, because the conductive agent content of the lithium supplement layer is high and the porosity is large, there is more electrolyte in the longitudinal lithium supplement material layer, so that the lithium ions of the positive electrode material can be quickly released through the electrolyte in the lithium supplement layer, thereby improving the concentration polarization during fast charging and discharging; in this way, the method not only maximizes the performance of the positive electrode active material and the lithium supplement agent, without affecting each other, but also maximizes the effect of the lithium supplement agent, thereby improving the energy density and cycle life of the battery cell; at the same time, the process is simple, can be flexibly designed according to the demand for lithium supplementation, and the coating of the positive electrode material and the lithium supplement agent is completed at one time, with low processing cost.

In order to achieve the above object, the present invention adopts the following technical solutions.

A lithium-replenishing positive electrode plate, comprising a positive current collector, a positive active material layer coated on the positive current collector, and a lithium-replenishing reagent layer, wherein a single lithium-replenishing reagent layer and a single positive active material layer are both arranged along the length direction of the current collector, and the lithium-replenishing reagent layer and the positive active material layer are arranged at intervals on the surface of the current collector along the width direction of the current collector.

As a preferred embodiment, the number of lithium replenishing reagent layers of the above-mentioned lithium replenishing positive electrode plate is adjusted according to the actual amount of lithium replenishment, the number of lithium replenishing reagent layers can be 1-5 (for example, 2, 3, 4), and the width of the lithium replenishing reagent layer is 0.5mm-30mm (for example, 1mm, 5mm, 10mm, 15mm, 20mm, 25mm).

As a preferred embodiment, the lithium-replenishing positive electrode plate comprises a lithium-replenishing reagent layer including a lithium-replenishing reagent, a first conductive agent, and a first binder.

As a preferred embodiment, the above-mentioned lithium-replenishing positive electrode plate, in the lithium-replenishing reagent layer, the lithium-replenishing reagent includes any one or more of _Li2S , _Li2O , _Li2O2 , _LiF , _{Li1 + a1FeO4} (0< _a1≤5 ), Li1 _{+a2NiO2 (} 0< _a2≤3 ), _{Li1 + a3NixCoyMnzO2} (0< _{a3≤3, 0≤x≤1} , 0≤y≤1, 0≤z≤1, and x+y+z＝1).

The above-mentioned lithium-supplemented positive electrode plate, as a preferred embodiment, in the lithium-supplementing reagent layer, the mass ratio of the lithium-supplementing reagent, the first conductive agent and the first binder is 60-95 (for example, 65, 70, 80, 85, 88): 2-30 (for example, 5, 10, 15, 20, 25, 28): 2-15 (for example, 3, 5, 10, 12, 14), and the sum of the ratios is equal to 100.

As a preferred embodiment, the thickness of the lithium-replenishing reagent layer of the above-mentioned lithium-replenishing positive electrode plate is the same as the thickness of the positive electrode active material, or is 1μm-20μm (for example, 3μm, 5μm, 10μm, 15μm, 18μm) lower than the thickness of the positive electrode active material.

In the present invention, the thickness of the lithium replenishing reagent layer is the same as or lower than the thickness of the positive electrode active material, especially the thickness of the lithium replenishing reagent layer is lower than the thickness of the positive electrode active material, which is beneficial to improving the liquid retention rate of the positive electrode plate, improving the concentration polarization of the positive electrode, and improving the discharge capacity and rate performance of the positive electrode.

As a preferred embodiment of the lithium-supplementing positive electrode sheet, the positive electrode active material layer and the lithium-supplementing reagent layer can be coated on any one side surface or both sides surface of the positive electrode current collector.

As a preferred embodiment, the lithium-replenishing positive electrode plate has 2-4 (for example, 3) lithium-replenishing reagent layers with a width of 1-10 mm (for example, 1 mm, 3 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm).

The above-mentioned lithium-supplemented positive electrode plate, as a preferred embodiment, the positive electrode active material layer comprises a positive electrode active material, a second conductive agent, and a second binder; wherein, in the positive electrode active material layer, by mass percentage, the positive electrode active material is 90-98% (for example, 92%, 94%, 95%, 97%), the second conductive agent is 0.5-5wt% (for example, 1wt%, 2wt%, 3wt%, 4wt%), and the second binder is 0.5-5wt% (for example, 1wt%, 2wt%, 3wt%, 4wt%).

As a preferred embodiment, the above-mentioned lithium-supplemented positive electrode plate has a mass ratio of the positive electrode active material layer and the lithium-supplementing reagent layer of (90-99):(1-10) (for example, 92:8, 94:6, 95:5, 96:4, 97:3, 98:2).

As a preferred embodiment, the above-mentioned lithium-supplemented positive electrode plate, in the positive electrode active material layer, the positive electrode active material includes one or more combinations of ternary positive electrode material Li _x M _y O ₂ (x is 1 to 2, y is 1 to 2), lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium manganese iron phosphate (LiMn _z Fe _1-z PO ₄ , z is 0.2-0.8), or doped positive electrode materials of the above materials, wherein M includes one or more of Ni, Mn, Co, Al, Mg, and Zr.

As a preferred embodiment of the lithium-supplemented positive electrode plate, the first binder or the second binder includes one or a combination of polyvinylidene fluoride, polytetrafluoroethylene, polyacrylic acid, lithium polyacrylate, sodium polyacrylate, carboxymethyl cellulose, and styrene-butadiene rubber.

As a preferred embodiment of the lithium-supplemented positive electrode plate, the first conductive agent or the second conductive agent includes at least one of conductive carbon black, acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, carbon nanotubes, graphene, metal powder or carbon fiber.

The present invention also provides a method for preparing the above-mentioned lithium-supplemented positive electrode plate, which adopts the following technical scheme.

A method for preparing the above-mentioned lithium-supplemented positive electrode sheet comprises the following steps:

(1) Preparation of positive electrode active material layer slurry

According to the above formula, the positive electrode active material, the second conductive agent and the second binder are added to the second solvent, and stirred sufficiently to obtain a positive electrode active material layer slurry;

(2) Preparation of lithium supplementation reagent layer slurry

According to the above formula, the lithium replenishing agent, the first conductive agent and the first binder are added to the first solvent, and stirred sufficiently to obtain an active slurry of the positive electrode lithium replenishing agent;

(3) Preparation of lithium-supplemented positive electrode sheets

According to the design requirements of the lithium-replenishing positive electrode sheet, the positive electrode active material layer slurry and the lithium-replenishing reagent layer slurry are coated on any one side or both sides of the positive electrode collector at one time to obtain the lithium-replenishing positive electrode sheet.

In the above-mentioned method for preparing the lithium-replenishing positive electrode sheet, as a preferred embodiment, in the step (3), the positive electrode active material layer slurry and the lithium-replenishing reagent layer slurry are coated on any one side or both sides of the positive electrode collector at one time by a conventional extrusion coater and a designed extrusion gasket to obtain the lithium-replenishing positive electrode sheet.

In the above-mentioned method for preparing the lithium-supplemented positive electrode sheet, as a preferred embodiment, in the step (3), after the positive electrode active material layer and the lithium-supplementing reagent layer are coated on one side of the positive electrode current collector, the positive electrode active material layer and the lithium-supplementing reagent layer are coated on the other side of the positive electrode current collector.

In the above-mentioned method for preparing the lithium-supplemented positive electrode sheet, as a preferred embodiment, the step (3) further comprises drying, cold pressing, slitting, and cutting after coating is completed to obtain the positive electrode sheet.

In the above-mentioned method for preparing the lithium-supplemented positive electrode sheet, as a preferred embodiment, in the step (1) or (2), the stirring is carried out in a vacuum mixer.

Since most positive electrode lithium replenishers have poor conductivity, such as Li ₂ S, Li ₂ O, Li ₂ O ₂ , LiF, Li ₅ FeO ₄ , and Li ₂ NiO ₂ , they must be combined with a higher proportion of conductive agents to effectively release the lithium ions they contain. If the positive electrode lithium replenisher is simply blended with the positive electrode active material, the lithium ions released by the lithium replenisher are lower than the theoretical capacity; in addition, due to the low-conductivity substances remaining after the lithium replenisher is de-lithiated, the resistance of the positive electrode sheet increases, which deteriorates the performance of the gram capacity of the positive electrode active material itself, and finally makes the energy density of the battery cell unsatisfactory. Therefore, the present invention separates the positive electrode active material and the lithium replenisher into slurries, matches different formulas according to their respective characteristics, and then applies the two slurries (coating) on the surface of one side of the positive electrode current collector at one time by extrusion coating. This method not only maximizes the performance of the positive electrode active material and the lithium replenisher without affecting each other, but also maximizes the effect of the lithium replenisher and improves the energy density and cycle life of the battery cell. At the same time, the process is simple and can be flexibly designed according to the amount of lithium replenishment. The positive electrode material and the lithium replenisher can be coated on the surface of one side of the positive electrode current collector at one time, and the processing cost is low.

In the present invention, in the step (3), the positive electrode active material layer slurry or the lithium replenishing reagent layer slurry can also be coated on one side or both sides of the positive electrode current collector, and then the lithium replenishing reagent layer slurry or the positive electrode active material layer slurry is coated on one side or both sides of the positive electrode current collector to obtain the lithium replenishing positive electrode plate; that is, the method of coating the positive electrode active material layer slurry or the lithium replenishing reagent layer slurry on one side or both sides of the positive electrode current collector is adopted.

Another aspect of the present invention provides a lithium-ion battery, comprising a positive electrode plate, a separator and a negative electrode plate, wherein the positive electrode plate adopts the above-mentioned lithium-supplementing positive electrode plate.

In the present invention, under the condition that they do not conflict with each other, the above technical features can be freely combined to form a new technical solution.

Compared with the prior art, the beneficial technical effects of the present invention are as follows:

1. The present invention separates and homogenizes the positive electrode active material and the lithium replenishing agent, matches different conductive agent contents according to their respective electronic conduction characteristics, and then applies the two slurries on the surface of one side of the positive electrode current collector at one time by extrusion coating. This not only maximizes the performance of the positive electrode active material and the lithium replenishing agent, but also does not affect each other, maximizes the effect of the lithium replenishing agent, and improves the energy density and cycle life of the battery cell;

2. The single lithium replenishing reagent layer is distributed longitudinally (perpendicular to the width direction of the current collector, i.e., arranged along the length direction of the current collector), which neither affects the electronic conduction between the positive electrode active material layer and the current collector, nor deteriorates the transmission path of lithium ions. At the same time, because the lithium replenishing reagent layer has a high content of conductive agent and a large porosity, there is more electrolyte in the longitudinal lithium replenishing reagent layer, so that the lithium ions of the positive electrode material can be quickly released through the electrolyte in the lithium replenishing reagent layer, thereby improving the concentration polarization during fast charging;

3. The preparation process of the lithium-supplemented positive electrode sheet in the present invention is simple, and can be flexibly designed according to different lithium replenishment amounts. The positive electrode active material layer and the lithium replenishment reagent layer are coated on the surface of one side of the positive electrode current collector at one time, and the processing cost is low.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a cross-sectional view of a positive electrode sheet of the present invention along the width direction of the current collector;

FIG2 is a top view of the positive electrode sheet of the present invention;

FIG3 is a schematic diagram of the positive and negative electrode sheets and the separator assembly of a lithium-ion battery (i.e., a battery cell) according to the present invention;

Explanation of reference numerals: 1 is a current collector; 2 is a lithium replenishing reagent layer; 3 is a positive electrode active material layer; 4 is a separator; 5 is a negative electrode plate.

DETAILED DESCRIPTION

The present invention will be described in detail below in conjunction with the embodiments. Each example is provided by way of explanation of the present invention and does not limit the present invention. In fact, it will be clear to those skilled in the art that modifications and variations may be made in the present invention without departing from the scope or spirit of the present invention. For example, a feature shown or described as a part of one embodiment may be used in another embodiment to produce yet another embodiment. Therefore, it is desired that the present invention includes such modifications and variations within the scope of the appended claims and their equivalents.

In the present invention, the reagents and materials, unless otherwise specified, can be obtained from commercial sources. In the present invention, parts not described in detail can adopt conventional technical solutions in the art.

As shown in the cross-sectional view and top view of the lithium-replenishing positive electrode sheet in Figures 1-2, a lithium-replenishing positive electrode sheet comprises a positive current collector 1, a lithium-replenishing reagent layer 2 coated on the surface of the positive current collector, and a positive electrode active material layer 3, wherein a single lithium-replenishing reagent layer and a single positive electrode active material layer are arranged along the length direction of the current collector, that is, the length directions of the lithium-replenishing reagent layer and the positive electrode active material layer formed on the surface of the current collector are consistent with the length direction of the current collector, and the lithium-replenishing reagent layer and the positive electrode active material layer are arranged at intervals on the surface of the current collector along the width direction of the current collector, that is, a plurality of lithium-replenishing reagent layers and a plurality of positive electrode active material layers arranged along the length direction of the current collector are included on one current collector, and the plurality of lithium-replenishing reagent layers and the plurality of positive electrode active material layers are alternately arranged along the width direction of the current collector.

As shown in FIG3 , a lithium-ion battery (i.e., a battery cell) includes a positive electrode plate, a separator 4 and a negative electrode plate 5 , wherein the positive electrode plate includes a positive electrode collector 1 , a lithium replenishing reagent layer 2 coated on the surface of the positive electrode collector, and a positive electrode active material layer 3 .

Example 1

Preparation of positive electrode

The positive electrode active material LiFePO ₄ , the conductive carbon black Super-P, and the binder PVDF are mixed in a N-methylpyrrolidone (NMP) solvent system in a weight ratio of 97.3:1.5:1.2 by a vacuum mixer to obtain a positive electrode active material layer slurry;

According to the formula, a lithium replenishing reagent, conductive carbon black and polyvinylidene fluoride (PVDF) are added to N-methylpyrrolidone NMP solvent and stirred thoroughly to obtain a lithium replenishing reagent layer slurry; in the dried positive electrode sheet, the lithium replenishing reagent layer accounts for 4% of the total weight of the positive electrode active material layer and the lithium replenishing reagent layer (i.e., the addition ratio of the lithium replenishing reagent layer); see Table 1 for details;

As shown in Figure 1, the positive electrode slurry and the lithium replenishing reagent layer slurry are coated on either side of a 12μm thick Al foil substrate at one time by a conventional extrusion coating machine and a designed extrusion gasket, and then the positive electrode slurry and the lithium replenishing reagent layer slurry are coated on the other side of the 12μm Al foil substrate at one time after drying, and then dried, cold pressed, striped, and cut to obtain a positive electrode sheet. Among them, the number of strips of the positive electrode active material layer is 3, each with a width of 20mm and a thickness of 186μm; the number of strips of the lithium replenishing reagent layer is 2, each with a width of 1.3mm and a thickness of 186μm.

Preparation of negative electrode

The negative electrode active material (95%wt graphite + 5%wt silicon carbon), conductive agent, styrene-butadiene rubber and sodium carboxymethyl cellulose (binder) are dissolved in deionized water in a weight ratio of 96.5:1:1.2:1.3, and the mixture is stirred and mixed to obtain a slurry containing the first negative electrode active material;

The negative electrode slurry and thermal conductive slurry containing the negative electrode active material are coated on the surface of the 6μm thick Cu foil of the negative electrode current collector by a specially designed extrusion coater. After drying, cold pressing and cutting, the negative electrode sheet with a double-layer active material layer is obtained. After cold pressing, the thickness of the negative electrode sheet is 130μm.

Preparation of electrolyte

Ethylene carbonate (EC), ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) are mixed in a volume ratio of 3:3:4 to obtain an organic solvent, and then fully dried _LiPF6 is dissolved in the mixed organic solvent to prepare an electrolyte with a _LiPF6 concentration of 1 mol/L.

Preparation of isolation membrane

The isolation membrane substrate is 8 μm thick polyethylene (PE), and a 2 μm alumina ceramic layer is coated on both sides of the isolation membrane substrate. Finally, 2.5 mg of polyvinylidene fluoride (PVDF) adhesive is coated on both sides of the ceramic layer and dried.

Preparation of lithium-ion secondary batteries

The positive electrode sheet, isolation film and negative electrode sheet are stacked in order, so that the isolation film is placed between the positive and negative electrode sheets to play an isolating role, and then wound to obtain a bare battery cell; the qualified bare battery cell is welded to the top cover through the pole ear, placed in an outer packaging shell, and injected with electrolyte after drying. After vacuum packaging, standing, forming, shaping and other processes, a soft-pack lithium-ion secondary battery with a capacity of about 5000mAh is obtained.

Example 2

The difference between Example 2 and Example 1 is that the positive electrode active material is LiNi _0.8 Co _0.1 Mn _0.1 O ₂ , and the lithium replenishing reagent layer accounts for 3% of the total mass of the positive electrode active material layer and the lithium replenishing reagent layer (that is, the addition ratio of the lithium replenishing reagent layer); the mass ratio of the positive electrode active material, the conductive carbon black and the polyvinylidene fluoride is 97.6:1.3:1.1, and the other technical schemes are the same as those in Example 1, see Table 1 for details.

In the positive electrode sheet prepared in this embodiment, the number of positive electrode active material layers is 3, each with a width of 20 mm and a thickness of 110 μm; the number of lithium supplement reagent layers is 2, each with a width of 1 mm and a thickness of 110 μm.

Example 3

The difference between Example 3 and Example 1 is that in the lithium replenishing reagent layer, the mass ratio of the lithium replenishing reagent, the conductive carbon black and the polyvinylidene fluoride is 95:3:2, and the other technical schemes are the same as those in Example 1, see Table 1 for details.

In the positive electrode sheet prepared in this embodiment, the number of positive electrode active material layers is 3, each with a width of 20 mm and a thickness of 186 μm; the number of lithium supplement reagent layers is 2, each with a width of 1.3 mm and a thickness of 186 μm.

Example 4

The difference between Example 4 and Example 1 is that the proportion of the lithium replenishing reagent layer to the total weight of the positive electrode active material layer and the lithium replenishing reagent layer is 3%; see Table 1 for details.

In the positive electrode sheet prepared in this embodiment, the number of positive electrode active material layers is 3, each with a width of 20 mm and a thickness of 186 μm; the number of lithium supplement reagent layers is 2, each with a width of 1.0 mm and a thickness of 186 μm. Other technical solutions are the same as those in Example 1.

Example 5

The difference between Example 5 and Example 4 is that the lithium supplementing agent is Li ₂ NiO ₂ , and the mass ratio of the lithium supplementing agent, conductive carbon black and polyvinylidene fluoride is 90:7:3. The other technical schemes are the same as those in Example 4, see Table 1 for details.

In the positive electrode sheet prepared in this embodiment, the number of positive electrode active material layers is 3, each with a width of 20 mm and a thickness of 186 μm; the number of lithium supplement reagent layers is 2, each with a width of 1.5 mm and a thickness of 110 μm;

Comparative Example 1

The difference between this comparative example and Example 1 is that in this comparative example, the positive electrode sheet does not contain a lithium supplementing reagent layer. Specifically,

Preparation of positive electrode

The positive electrode active material-LiFePO ₄ , conductive carbon black Super-P, and binder PVDF are fully stirred in a N-methylpyrrolidone (NMP) solvent system in a weight ratio of 97.3:1.5:1.2 by a vacuum mixer to obtain a positive electrode slurry; the positive electrode slurry is coated on both surfaces of a 12 μm thick Al foil substrate, and then dried, cold pressed, slit, and cut to obtain a positive electrode sheet.

In the positive electrode sheet prepared in this comparative example, the positive electrode active material layer is spread on both side surfaces of the positive electrode current collector, and the thickness is 186 μm.

Comparative Example 2

The difference between this comparative example and Example 2 is that in this comparative example, the positive electrode plate does not contain a lithium replenishing reagent layer, and the positive electrode slurry is coated on both surfaces of a 12 μm thick Al foil substrate to form a positive electrode plate having a positive electrode active material layer flattened on both side surfaces of the Al foil substrate.

In the positive electrode sheet prepared in this comparative example, the positive electrode active material layer is spread on both side surfaces of the positive electrode current collector, and the thickness is 110 μm.

Comparative Example 3

The difference between this comparative example and Example 1 is that in this comparative example, the coating method of the positive electrode active material layer and the lithium replenishing reagent layer on the surface of the positive electrode current collector is different. In this comparative example, the lithium replenishing reagent layer and the positive electrode active material layer are stacked along the height or thickness direction of the positive electrode current collector. Specifically:

The positive electrode active material slurry is coated on both surfaces of a 12 μm thick Al foil substrate to obtain a positive electrode current collector having positive electrode active material layers on both sides of the substrate; after drying, the lithium replenishing reagent layer slurry is coated on the surface of the positive electrode active material layer; and through drying, cold pressing, striping and cutting, a positive electrode sheet having positive electrode active material layers and lithium replenishing reagent layers sequentially coated on both sides of the current collector is obtained.

In this comparative example, the thickness of the positive electrode active material layer of the obtained positive electrode sheet was 186 μm, and the thickness of the lithium replenishing agent layer was 8 μm.

Comparative Example 4

The difference between this comparative example and Example 1 is that in this comparative example, the coating method of the positive electrode active material layer and the lithium replenishing reagent layer on the surface of the positive electrode current collector is different. In this comparative example, the lithium replenishing reagent layer and the positive electrode active material layer are stacked along the height or thickness direction of the positive electrode current collector. Specifically:

The lithium replenishing reagent layer slurry is coated on the two surfaces of a 12 μm thick Al foil substrate to obtain a positive electrode current collector with lithium replenishing reagent layers on both sides of the substrate; after drying, the positive electrode active material slurry is coated on the surface of the lithium replenishing reagent layer; through drying, cold pressing, striping and cutting, a positive electrode sheet with the lithium replenishing reagent layer and the positive electrode active material layer sequentially coated on the two sides of the positive electrode current collector is obtained.

In this comparative example, the thickness of the positive electrode active material layer of the obtained positive electrode sheet is 186 μm; the thickness of the lithium supplement reagent layer is 8 μm.

Electrochemical performance test of batteries

At 25°C, the battery was discharged to 2.75V at 1C, left to stand for 1 hour, charged to 4.2V at 1C, left to stand for 1 hour, then discharged to 2.75V at 1C and the 1C discharge capacity (i.e., the capacity at the first cycle) was detected, and the capacity retention rate was calculated by dividing the capacity after 500 cycles by the capacity at the first cycle; charged at a rate of 0.33C, and then discharged at a rate of 0.33C, and the 0.33C energy density was obtained by multiplying the capacity by the average voltage during discharge. Table 1 lists the main process parameters and electrochemical properties of Examples 1-5 and Comparative Examples 1-4.

Table 1 Main process parameters and electrochemical performance of Examples 1-5 and Comparative Examples 1-4

Claims (10)

1. A lithium-replenishing positive electrode sheet, characterized in that the lithium-replenishing positive electrode sheet comprises a positive current collector, a positive active material layer coated on the positive current collector, and a lithium-replenishing reagent layer, wherein a single lithium-replenishing reagent layer and a single positive active material layer are both arranged along the length direction of the current collector, and the lithium-replenishing reagent layer and the positive active material layer are arranged at intervals on the surface of the current collector along the width direction of the current collector. 2. The lithium-supplementing positive electrode sheet according to claim 1, characterized in that the number of lithium-supplementing reagent layers is adjusted according to the actual amount of lithium supplementation, the number of lithium-supplementing reagent layers is 1-5, and the width of the lithium-supplementing reagent layers is 0.5 mm-30 mm; and/or, The positive electrode active material layer and the lithium supplementing agent layer may be coated on any one side surface or both sides surface of the positive electrode current collector. 3. The lithium-supplemented positive electrode sheet according to claim 1 or 2, characterized in that the lithium-supplementing reagent layer comprises a lithium-supplementing reagent, a first conductive agent, and a first binder; the positive electrode active material layer comprises a positive electrode active material, a second conductive agent, and a second binder; _In the lithium replenishing reagent layer, the lithium replenishing reagent includes any one or more of _Li2S , Li2O, _Li2O2 , LiF, Li1 _{+ a1FeO4} (0< _a1≤5 ), Li1 _{+ a2NiO2} (0<a2≤3), Li1 _{+a3NixCoyMnzO2 (} 0 _{< a3≤3,} 0≤x≤1, 0≤y≤1, 0≤z≤1, and x ₊ y _{+ z} ＝ ₁ ); and/or, In the positive electrode active material layer, the positive electrode active material includes a ternary positive electrode material Li _{x My} O ₂ , one or more combinations of lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, or a doped positive electrode material of the above materials, wherein M includes one or more of Ni, Mn, Co, Al, Mg, and Zr, x is 1 to 2, and y is 1 to 2; and/or, The first binder or the second binder includes one or a combination of polyvinylidene fluoride, polytetrafluoroethylene, polyacrylic acid, lithium polyacrylate, sodium polyacrylate, carboxymethyl cellulose, and styrene-butadiene rubber; and/or, The first conductive agent or the second conductive agent includes at least one of conductive carbon black, acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, carbon nanotube, graphene, metal powder or carbon fiber. 4. The lithium-supplemented positive electrode plate according to claim 3, characterized in that: In the lithium replenishing reagent layer, the mass ratio of the lithium replenishing reagent, the first conductive agent and the first binder is 60-95:2-30:2-15, and the sum of the ratios is equal to 100; and/or, In the positive electrode active material layer, by mass percentage, the positive electrode active material is 90-98%, the second conductive agent is 0.5-5wt%, and the second binder is 0.5-5wt%; and/or, The mass ratio of the positive electrode active material layer to the lithium supplement reagent layer is (90-99):(1-10). 5 . The lithium-supplementing positive electrode plate according to claim 2 , characterized in that the lithium-supplementing reagent layer has 2 to 4 strips and a width of 1 to 10 mm. 6 . The lithium-supplementing positive electrode sheet according to claim 1 , wherein the thickness of the lithium-supplementing reagent layer is the same as the thickness of the positive electrode active material, or is 1 μm-20 μm lower than the thickness of the positive electrode active material. 7. A method for preparing a lithium-supplemented positive electrode sheet according to any one of claims 1 to 6, characterized in that the preparation method comprises the following steps: (1) Preparation of positive electrode active material layer slurry Adding the positive electrode active material, the second conductive agent and the second binder into the second solvent according to the formula, and stirring them sufficiently to obtain a positive electrode active material layer slurry; (2) Preparation of lithium supplementation reagent layer slurry Adding the lithium replenishing agent, the first conductive agent and the first binder into the first solvent according to the formula, and stirring them sufficiently to obtain an active slurry of the positive electrode lithium replenishing agent; (3) Preparation of lithium-supplemented positive electrode sheets According to the design requirements of the lithium-replenishing positive electrode sheet, the positive electrode active material layer slurry and the lithium-replenishing reagent layer slurry are coated on any one side or both sides of the positive electrode collector at one time to obtain the lithium-replenishing positive electrode sheet. 8. The method for preparing a lithium-supplemented positive electrode sheet according to claim 7, characterized in that: In the step (1) or (2), the stirring is performed in a vacuum mixer; and/or, In the step (3), the positive electrode active material layer slurry and the lithium replenishing reagent layer slurry are coated on any one side or both sides of the positive electrode current collector at one time by an extrusion coater and a designed extrusion gasket to obtain the lithium replenishing positive electrode sheet. 9. The method for preparing a lithium-supplemented positive electrode sheet according to claim 7 or 8, characterized in that: After coating is completed, step (3) further comprises drying, cold pressing, slitting, and cutting to obtain positive electrode sheets. 10. A lithium-ion battery, characterized in that the lithium-ion battery comprises a positive electrode sheet, a separator and a negative electrode sheet, and the positive electrode sheet is the lithium-supplemented positive electrode sheet according to any one of claims 1 to 6.

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