Lithium supplement and preparation method thereof and lithium ion battery

Abstract

The present invention belongs to the technical field of lithium ion batteries, and specifically relates to a lithium supplement agent, a preparation method thereof, and a lithium ion battery. The lithium supplement agent comprises a conductive polymer and lithium doped in the conductive polymer, wherein the conductivity of the conductive polymer is 10 ‑9 ‑10 3 The lithium replenisher provided by the present invention can be used as both a positive electrode lithium replenisher and a negative electrode lithium replenisher, thereby reducing the impact on battery weight.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium ion batteries, and in particular relates to a lithium supplement agent, a preparation method thereof, and a lithium ion battery. Background Art

[0002] The working principle of the battery is that the positive electrode loses lithium ions during the charging phase, while the negative electrode gains lithium ions during the charging phase; during the discharging phase, the negative electrode loses lithium ions and the positive electrode gains lithium ions. The movement of lithium ions between the positive and negative electrodes converts the chemical energy of the battery into electrical energy. As we all know, the energy conversion process is often accompanied by energy loss. During the charging phase, lithium ions first form a solid electrolyte interface on the surface of the negative electrode. This is a proton membrane that only allows lithium ions to pass through. It is irreversible and will lead to lithium ion loss in the battery system. In addition, during long cycles of graphite negative electrode materials, organic molecules in the electrolyte will enter the lattice gaps, blocking the lithium ion entry and exit channels, resulting in the loss of active lithium. Various side reactions that occur in the battery during long cycles will also lead to lithium loss.

[0003] In order to replenish the lithium loss in the battery, the positive electrode lithium replenishment method is one of the commonly used lithium replenishment methods. The positive electrode lithium replenishment method is a positive electrode lithium replenisher method in which a positive electrode active material with a high lithium content and very low reversible capacity is selected and mixed with a traditional positive electrode active material in a certain proportion and used as a new positive electrode active material for battery assembly. For example, lithium replenishers such as Li2NiO2, Li5FeO4 or Li2O (conventional positive electrode lithium replenishers) are used to replenish the lithium consumed by the positive electrode. The principle is to utilize the irreversible characteristics of lithium-containing compounds (lithium replenishers) after losing lithium, and can only provide lithium ions to the system, and no longer participate in subsequent reactions. The disadvantage is that these lithium replenishers can usually only be used as positive electrode lithium replenishers, but not as negative electrode lithium replenishers, and have no effect once lithium is lost. When the amount of lithium replenishment is large, it will have a greater impact on the weight of the battery, thereby reducing the energy density of the battery. For example, patent publication number CN114497514A discloses a Li5FeO4 positive electrode lithium supplement with a coating layer. This supplement can only be used as a positive electrode lithium supplement, not as a negative electrode lithium supplement. Furthermore, when the amount of lithium supplemented is large, it significantly affects the weight of the battery, thereby reducing the battery's energy density. Therefore, developing a lithium supplement that can serve as both a positive and negative electrode lithium supplement while reducing the impact on battery weight is an urgent technical problem in this field. Summary of the Invention

[0004] In view of the above-mentioned deficiencies in the prior art, the present invention aims to provide a lithium supplement agent, a preparation method thereof, and a lithium-ion battery. The lithium supplement agent provided by the present invention can be used as both a positive electrode lithium supplement agent and a negative electrode lithium supplement agent, thereby reducing the impact on battery weight.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] In a first aspect, the present invention provides a lithium supplement, comprising a conductive polymer and lithium doped in the conductive polymer, wherein the conductivity of the conductive polymer is 10 -9 -10 3 S / cm (for example, it can be 10 -9 S / cm, 10 -5 S / cm, 10 -3 S / cm, 10S / cm or 10 3 S / cm, etc.).

[0007] Here, the conductive polymer may be an undoped conductive polymer, including at least one of polyacetylene (PA), polypyrrole (PPy), polythiophene (PTh), polyaniline (PAn), polyparaphenylene (PPP), and polyparaphenylenevinylene (PPV).

[0008] The lithium replenisher provided by the present invention can be used as both a positive electrode lithium replenisher and a negative electrode lithium replenisher, and can reduce the impact on battery weight.

[0009] In the above lithium supplement, as a preferred embodiment, based on the total mass of the lithium supplement being 100%, the mass percentage of lithium is 1%-50%, for example, 1%, 5%, 10%, 20%, 30%, 40% or 50%.

[0010] In the above lithium supplement, as a preferred embodiment, the lithium in the lithium supplement is released in the initial stage of the battery or is gradually released.

[0011] In a second aspect, the present invention provides a method for preparing the lithium supplement according to the first aspect, comprising the following steps:

[0012] S1, first pressing the conductive polymer into a sheet, and then placing a lithium source on the conductive polymer sheet;

[0013] S2. Connecting the conductive polymer sheet to the negative electrode of an external power source, connecting the lithium source to the positive electrode of the external power source, applying current to the conductive polymer sheet and the lithium source to complete lithium doping and obtain the lithium supplement.

[0014] The preparation principle of the lithium supplement provided by the present invention is to dope lithium ions into the conductive polymer molecular chain through interfacial charge injection doping. This preparation method has a simple manufacturing process and is suitable for mass production. The lithium content of the lithium supplement is controllable, and the lithium ions are present in the molecular chain, which has higher safety performance.

[0015] In the above-mentioned preparation method of the lithium supplement, as a preferred embodiment, during the process of pressing the conductive polymer into tablets, the pressure is 0.01-0.5 tons (for example, it can be 0.01 tons, 0.1 tons, 0.3 tons or 0.5 tons, etc.), and the tableting standard is that it will not break when picked up and can be easily ground into powder.

[0016] In the above method for preparing a lithium supplement, as a preferred embodiment, the thickness of the conductive polymer sheet is 0.1-100 mm (eg, 0.1 mm, 1 mm, 3 mm, 10 mm, 30 mm, 50 mm, 70 mm or 100 mm), preferably 0.1-10 mm.

[0017] In the above-mentioned method for preparing the lithium supplement, as a preferred embodiment, the lithium source is a lithium metal sheet, a lithium-copper composite strip or lithium powder.

[0018] In the above-mentioned method for preparing the lithium supplement, as a preferred embodiment, the lithium source is disposed on both sides of the conductive polymer sheet.

[0019] In the above-mentioned preparation method of lithium supplement, as a preferred embodiment, in step S2, the current density is 10-1000mA / cm 2 (For example, it can be 10mA / cm 2 、30mA / cm 2 , 50mA / cm 2 , 100mA / cm 2 、300mA / cm 2 , 500mA / cm 2 , 700mA / cm 2 or 1000mA / cm 2 wait).

[0020] In the above-mentioned method for preparing the lithium supplement, as a preferred embodiment, in step S2, the current density of the doping process decreases as the lithium ion doping concentration increases.

[0021] In the above method for preparing a lithium supplement, as a preferred embodiment, in step S2, the lithium source is in contact with the metal current collector plate, so that the lithium source is connected to the positive electrode of an external power source through the metal current collector plate.

[0022] In the above-mentioned method for preparing the lithium supplement, as a preferred embodiment, the metal current collector plate is a stainless steel plate, a copper plate or an aluminum alloy plate.

[0023] In the above-mentioned method for preparing a lithium supplement, as a preferred embodiment, in step S2, a force of 0-1000N and not 0N (for example, 10N, 30N, 50N, 70N, 100N, 300N, 500N, 700N or 1000N, etc.) is applied to the metal current collector plate to make the metal current collector plate in close contact with the lithium source.

[0024] In the above-mentioned method for preparing the lithium supplement agent, as a preferred embodiment, in step S2, the lithium-doped conductive polymer is ground into powder to obtain the lithium supplement agent.

[0025] In a third aspect, the present invention provides a lithium-ion battery comprising a positive electrode sheet and a negative electrode sheet, wherein the active material on the positive electrode sheet comprises a positive electrode active material A, and the lithium supplement provided by the first aspect or the lithium supplement prepared by the preparation method provided by the second aspect; and / or, the active material on the negative electrode sheet comprises a negative electrode active material B, and the lithium supplement provided by the first aspect or the lithium supplement prepared by the preparation method provided by the second aspect.

[0026] In the above lithium-ion battery, as a preferred embodiment, the amount of the lithium supplement agent is determined by the pre-lithium amount.

[0027] Here, the pre-lithiation amount may refer to the mass of lithium required to achieve the purpose of pre-lithiation.

[0028] In the above lithium-ion battery, as a preferred embodiment, the amount of the lithium supplement agent is the sum of the pre-lithium amount and the mass of the conductive polymer.

[0029] In the above lithium-ion battery, as a preferred embodiment, the calculation formula for the pre-lithium amount is selected from at least one of the following:

[0030] M Li =(CE1-CE0)*A1 / C Li (1), A1 is the design capacity of the battery, CE1 is the design first coulombic efficiency of the battery, CE0 is the actual first coulombic efficiency of the battery, M Li is the mass of lithium required, C Li is the theoretical specific capacity of lithium;

[0031] M Li =(A0(σ1-σ2)) / C Li (2), A0 is the design capacity of the battery, σ1 is the capacity retention rate after theoretical N cycles, σ2 is the capacity retention rate after actual N cycles, M Li is the mass of lithium required, C Li is the theoretical specific capacity of lithium.

[0032] When the purpose of pre-lithiation is to improve the initial coulombic efficiency of the battery, the calculation formula for the pre-lithiation amount is selected from formula (1); when the purpose of pre-lithiation is to improve the cycle performance of the battery, the calculation formula for the pre-lithiation amount is selected from formula (2).

[0033] In the above lithium-ion battery, as a preferred embodiment, the mass calculation formula of the conductive polymer is as follows: Where m is the mass of the conductive polymer and σ is the mass percentage of lithium in the lithium supplement.

[0034] In the above lithium-ion battery, as a preferred embodiment, the positive electrode active material A includes at least one of lithium iron phosphate, lithium cobalt phosphate, lithium manganese iron phosphate, and a ternary material.

[0035] In the above lithium-ion battery, as a preferred embodiment, the negative electrode active material B includes at least one of graphite, silicon-oxygen negative electrode, silicon-oxygen-graphite negative electrode, and silicon-carbon-graphite.

[0036] In the above-mentioned lithium-ion battery, as a preferred embodiment, the method for preparing the positive electrode sheet includes: mixing the positive electrode active material A, the conductive agent, the binder and the lithium supplement agent in a solvent to prepare a positive electrode slurry, then coating the positive electrode slurry on the positive electrode collector, and then drying, rolling and die-cutting to obtain the positive electrode sheet.

[0037] In the above-mentioned lithium-ion battery, as a preferred embodiment, the method for preparing the negative electrode sheet includes: mixing the negative electrode active material B, the conductive agent, the binder and the lithium supplement agent in a solvent to prepare a negative electrode slurry, then coating the negative electrode slurry on the negative electrode collector, and then drying, rolling and die-cutting to obtain the negative electrode sheet.

[0038] In the above lithium-ion battery, as a preferred embodiment, when the lithium replenisher is used as a positive electrode lithium replenisher, the mass ratio of the positive electrode active material A, conductive agent, binder, and lithium replenisher is (80-99.5): (0.1-10): (0.2-5): (0.1-5).

[0039] In the above lithium-ion battery, as a preferred embodiment, when the lithium replenisher is used as a negative electrode lithium replenisher, the mass ratio of the negative electrode active material B, the conductive agent, the binder, and the lithium replenisher is (70-97): (0.5-12): (1-12): (0.5-6).

[0040] In the above lithium-ion battery, as a preferred embodiment, the conductive agent includes at least one of acetylene black, Super P, Ketjen black, VGCF, graphene, graphene composite conductive paste, carbon nanotubes, and carbon nanotube conductive paste.

[0041] In the above-mentioned lithium-ion battery, as a preferred embodiment, the binder for the positive electrode plate includes at least one of polyvinylidene fluoride (PVDF), polybutylene acrylate (PBA), polyacrylonitrile (PA), polyethylene oxide (PEO), and polyvinyl alcohol (PVA).

[0042] In the above lithium-ion battery, as a preferred embodiment, the binder for the negative electrode plate includes at least one of sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyimide (PI), and polyacrylic acid (PAA).

[0043] Compared with the prior art, the present invention has at least one of the following advantages:

[0044] (1) The lithium replenisher provided by the present invention can be used as both a positive electrode lithium replenisher and a negative electrode lithium replenisher, thereby reducing the impact on battery weight.

[0045] (2) The lithium supplement provided by the present invention has a controllable lithium content and a simple manufacturing process. Since the conductive polymer itself has high viscosity and conductivity, it can also replace some binders and conductive agents, reducing the binder and conductive agent content in the positive and negative electrodes, thereby increasing the proportion of active material and achieving higher energy density.

[0046] (3) The conductive polymer lithium supplement provided by the present invention has higher safety performance. Lithium ions exist in the molecular chain and will only be dedoped under the action of an electric field. Therefore, it has no restrictions on the use environment, the preparation process is simple, and it is suitable for mass production.

[0047] (4) After the conductive polymer lithium supplement is doped with lithium, as the doping concentration increases, the conductivity of the conductive polymer approaches that of metal. It can not only serve as a lithium supplement, but also as a conductive agent.

[0048] (5) Conductive polymers are high molecular materials with a certain viscosity. As the amount of lithium supplementation increases, the use of binders can be reduced.

[0049] (6) Other lithium replenishing materials (such as conventional positive electrode lithium replenishing agents) not only increase the weight of the battery but also make the lithium replenishment uncontrollable. Excessive lithium replenishment will reduce the safety factor of the battery. The biggest advantage of the lithium replenishing agent provided by the present invention is that it will not significantly affect the energy density of the battery. Even if the amount of lithium replenishment is too high, the excess lithium will only exist in the molecular chain, providing conductivity for the battery, and will not increase safety hazards to the battery.

[0050] (7) The conductive polymer lithium supplement is directly mixed with the positive and negative electrode slurries, and its pre-lithiation uniformity is better than most pre-lithiation methods, such as electrochemical pre-lithiation, electrolyte pre-lithiation, and diaphragm pre-lithiation. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1is a circuit diagram of the doping process in Example 1;

[0052] Figure 2 This is the first charge and discharge curve of the battery in Example 1;

[0053] Figure 3 This is the first charge and discharge curve of the battery in Comparative Example 1.

[0054] The attached figure indicates: 1-lithium sheet; 2-polyacetylene sheet; 3-metal current collector plate. DETAILED DESCRIPTION

[0055] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention.

[0056] The embodiments of the present invention are implemented on the premise of the technical solution of the present invention, and detailed implementation methods and processes are given. However, the scope of protection of the present invention is not limited to the following embodiments. The process parameters in the following embodiments that do not specify specific conditions are generally based on conventional conditions.

[0057] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to form one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed in the present invention.

[0058] Throughout this disclosure, unless otherwise specified and / or explained, all references to component amounts are in parts by weight. Process parameters in the following examples, where specific conditions are not specified, generally follow conventional conditions. The experimental reagents used in the following examples, unless otherwise noted, are conventional biochemical reagents; and the amounts of experimental reagents used, unless otherwise noted, are those used in routine experimental procedures.

[0059] In a first aspect, an embodiment of the present invention provides a lithium supplement agent, wherein the lithium supplement agent comprises a conductive polymer and lithium doped in the conductive polymer, wherein the total mass of the lithium supplement agent is 100%, the mass percentage of the lithium is 1%-50%, and the conductivity of the conductive polymer is 10 -9 -10 3S / cm, the lithium in the lithium supplement is released or gradually released in the initial stage of the battery, and the conductive polymer can be an undoped conductive polymer, including at least one of polyacetylene (PA), polypyrrole (PPy), polythiophene (PTh), polyaniline (PAn), polyparaphenylene (PPP), and polyparaphenylene vinylene (PPV).

[0060] The preparation principle of the conductive polymer lithium supplement of the present invention is to dope lithium ions into the conductive polymer molecular chain through interfacial charge injection doping. The doped conductive polymer can undergo P-type dedoping under the action of an external electric field to remove lithium ions to replenish the lithium loss in the battery. The basic chemical reaction formula is as follows: Where CP stands for conductive polymer.

[0061] When the lithium replenisher is a mixture of a conductive polymer and inert lithium powder, the lithium replenisher can only be used as a negative electrode lithium replenisher. At this time, the conductive polymer has almost no effect on the pre-lithium effect and only increases the weight of the battery.

[0062] In the existing technology, the negative electrode lithium replenishment method is to perform electrochemical pre-lithiation through lithium foil, or to replenish lithium by rolling lithium foil, or to replenish lithium with inert lithium powder. The disadvantage is that the lithium replenishment environment requirements are extremely high and the lithium replenishment content cannot be accurately controlled.

[0063] In a second aspect, an embodiment of the present invention provides a method for preparing the lithium supplement according to the first aspect, comprising the following steps:

[0064] S1. First, press the conductive polymer into a sheet, and then place a lithium source on the conductive polymer sheet with a thickness of 0.1-100 mm. During the process of pressing the conductive polymer into a sheet, the pressure is 0.01-0.5 tons. The standard for making the sheet is that it will not break when picked up and can be easily ground into powder. The lithium source is a lithium metal sheet, a lithium-copper composite strip or lithium powder. The lithium source is placed on both sides of the conductive polymer sheet.

[0065] S2, connecting the conductive polymer sheet to the negative electrode of an external power source, connecting the lithium source to the positive electrode of the external power source, applying current to the conductive polymer sheet and the lithium source to complete lithium doping, grinding the lithium-doped conductive polymer into powder to obtain the lithium supplement, with a current density of 10-1000 mA / cm 2 The current density of the doping process decreases with the increase of the lithium ion doping concentration. The lithium source is in contact with the metal current collector plate so that the lithium source is connected to the positive electrode of the external power supply through the metal current collector plate. The metal current collector plate is a stainless steel plate, a copper plate or an aluminum alloy plate. A force of 0-1000N and not 0N is applied to the metal current collector plate to ensure close contact between the metal current collector plate and the lithium source.

[0066] In a third aspect, an embodiment of the present invention provides a lithium-ion battery, comprising a positive electrode sheet and a negative electrode sheet, wherein the active material on the positive electrode sheet comprises a positive electrode active material A, and the lithium supplement provided by the first aspect or the lithium supplement prepared by the preparation method provided by the second aspect; and / or, the active material on the negative electrode sheet comprises a negative electrode active material B, and the lithium supplement provided by the first aspect or the lithium supplement prepared by the preparation method provided by the second aspect, wherein the amount of the lithium supplement is determined by the pre-lithium amount, and the amount of the lithium supplement is the sum of the pre-lithium amount and the mass of the conductive polymer; the mass of the conductive polymer is calculated as follows: Wherein, m is the mass of the conductive polymer, σ is the mass percentage of lithium in the lithium supplement; the positive electrode active material A includes at least one of lithium iron phosphate, lithium cobalt phosphate, lithium manganese iron phosphate, and a ternary material; the negative electrode active material B includes at least one of graphite, silicon oxide negative electrode, silicon oxide graphite negative electrode, and silicon carbon graphite;

[0067] The calculation formula of the pre-lithium amount is selected from at least one of the following:

[0068] M Li =(CE1-CE0)*A1 / C Li (1), A1 is the design capacity of the battery, CE1 is the design first coulombic efficiency of the battery, CE0 is the actual first coulombic efficiency of the battery, M Li is the mass of lithium required, C Li is the theoretical specific capacity of lithium;

[0069] M Li =(A0(σ1-σ2)) / C Li (2), A0 is the design capacity of the battery, σ1 is the capacity retention rate after theoretical N cycles, σ2 is the capacity retention rate after actual N cycles, M Li is the mass of lithium required, C Li is the theoretical specific capacity of lithium;

[0070] The method for preparing the positive electrode sheet comprises: mixing the positive electrode active material A, a conductive agent, a binder and the lithium supplement agent in a solvent to prepare a positive electrode slurry, then coating the positive electrode slurry on a positive electrode current collector, and then drying, rolling and die-cutting to obtain the positive electrode sheet;

[0071] The method for preparing the negative electrode sheet comprises: mixing the negative electrode active material B, a conductive agent, a binder and the lithium supplement agent in a solvent to prepare a negative electrode slurry, then coating the negative electrode slurry on a negative electrode current collector, and then drying, rolling and die-cutting to obtain the negative electrode sheet;

[0072] When the lithium replenisher is used as a positive electrode lithium replenisher, the mass ratio of the positive electrode active material A, the conductive agent, the binder, and the lithium replenisher is (80-99.5): (0.1-10): (0.2-5): (0.1-5);

[0073] When the lithium replenisher is used as a negative electrode lithium replenisher, the mass ratio of the negative electrode active material B, the conductive agent, the binder, and the lithium replenisher is (70-97): (0.5-12): (1-12): (0.5-6);

[0074] The conductive agent includes at least one of acetylene black, Super P, Ketjen black, VGCF, graphene, graphene composite conductive paste, carbon nanotubes, and carbon nanotube conductive paste;

[0075] The positive electrode sheet binder includes at least one of polyvinylidene fluoride (PVDF), polybutyl acrylate (PBA), polyacrylonitrile (PA), polyethylene oxide (PEO), and polyvinyl alcohol (PVA);

[0076] The binder for the negative electrode sheet includes at least one of sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyimide (PI), and polyacrylic acid (PAA).

[0077] In order to further understand the present invention, the lithium supplement agent, preparation method thereof, and lithium ion battery provided by the present invention are described in detail below with reference to the examples. The protection scope of the present invention is not limited by the following examples.

[0078] In the following examples and comparative examples:

[0079] The first coulombic efficiency test method:

[0080] The prepared battery was subjected to charge and discharge tests, and constant current charging was performed at a current of 0.2C. The charging limit was 50% SOC of the battery design capacity. The charging capacity FC1 of the battery was recorded. The battery was left to stand at 45°C for 12 hours, and the battery was continued to be charged and discharged. The process steps were: constant current charging at 0.2C to 3.65V, and then constant voltage charging to a cutoff current of 0.05C, and the charging capacity was recorded as FC2; discharging at a constant current of 0.2C to a cutoff voltage of 2V, and the discharge capacity DC3 was recorded. The first coulombic efficiency = DC3 / (FC2+FC1).

[0081] Test method for cycle performance (capacity retention):

[0082] The prepared battery was subjected to charge and discharge tests. The test steps were: constant current charging at 0.33C to 3.65V, followed by constant voltage charging to a cutoff current of 0.05C; and then constant current discharge at 0.33C to a cutoff voltage of 2V. This process cycle was repeated, and the ratio of the discharge capacity in the Nth cycle to the discharge capacity in the first cycle was the battery's capacity retention rate; a higher ratio indicates better cycle performance.

[0083] Peel strength test method:

[0084] Cut the negative electrode into test samples of 90x120mm size, and stick the cut electrode to the middle of the thin steel plate with double-sided tape, with the end faces flush. The thin steel plate should be wiped clean with dust-free paper in advance to leave no stains or dust. Peel off one end of the sample, bend it 180° in the opposite direction, and fix it on the tensile probe. Peel it 180° at a constant rate of 5cm / min to test the peel strength of the sample.

[0085] Diaphragm (electrode) resistance test method: Use ACCFILM diaphragm resistance tester to test the diaphragm resistance of the electrode. Cut the electrode into a disc with a diameter of 25mm and place it under the test probe. The test pressure is 0.3t and the holding time is 2s to obtain the measured diaphragm resistance data.

[0086] Comparative Example 1

[0087] The design capacity of the lithium-ion battery provided in this comparative example is 20 Ah.

[0088] The method for preparing a lithium-ion battery provided in this comparative example comprises the following steps:

[0089] S1. Preparation of positive electrode sheet:

[0090] Lithium iron phosphate, SP, carbon nanotubes, and PVDF were slurried in a mass ratio of 96.5:1:0.5:2. PVDF and NMP were first combined to prepare a paste, followed by the addition of SP and carbon nanotubes, which were then dispersed at high speed. Finally, the lithium iron phosphate was added and dispersed at high speed to complete the slurry. The slurry was then coated, rolled, and die-cut to produce the positive electrode sheet.

[0091] S2. Preparation of lithium-ion batteries:

[0092] The positive electrode and negative electrode sheets prepared in step S1 and the 9 μm polypropylene separator were stacked to obtain a battery cell, and then the electrolyte was injected and assembled to obtain a lithium-ion battery. The electrolyte used was 1 mol / L LiPF6 / EC+EMC+DMC (volume ratio of 1:1:1) electrolyte.

[0093] The initial coulombic efficiency of the lithium-ion battery prepared in this comparative example is 90%.

[0094] Example 1

[0095] The purpose of this embodiment is to improve the initial coulombic efficiency of the lithium-ion battery prepared in Comparative Example 1. In this embodiment, the conductive polymer lithium replenisher is used as the positive electrode lithium replenisher, and the positive electrode active material is lithium iron phosphate. The lithium replenisher is used as the positive electrode lithium replenisher to improve the initial coulombic efficiency of the battery. The design capacity of the battery is 20Ah, the expected initial efficiency is CE2=96%, and the actual initial efficiency is CE1=90%. The lithium replenishment amount (preliminary lithium amount) of the battery is M li =0.31g, replenished capacity C0=1.2Ah, the mass percentage of lithium in the lithium replenisher σ=20%, and the mass of the conductive polymer m=1.24g is calculated.

[0096] Figure 1 is a circuit diagram of the doping process in Example 1, as shown Figure 1 As shown, the preparation method of the conductive polymer lithium supplement provided in this embodiment includes the following steps:

[0097] S1, weigh 1.24g of polyacetylene (conductivity 10 -2 S / cm), placed in the circular tablet press slot, pressed into an area of ​​10cm 2 The polyacetylene sheet 2 has a pressure of 0.15 tons and a thickness of 1.5 mm. The round lithium sheet 1 with a total weight of 0.31 g is weighed, and there are 2 pieces in total (each piece weighs 0.31 / 2 g). The area of ​​the lithium sheet 1 is 10 cm 2 , two lithium sheets 1 are clamped between the two ends of the above-mentioned polyacetylene sheet 2.

[0098] S2, clamp the stainless steel metal collector plate 3 between the two ends of the lithium sheet 1, and apply a force of 30N to press the metal collector plate 3, according to Figure 1 Circuit diagram, using 10mA / cm 2 The constant current pre-lithiation is carried out for 12 hours to achieve lithium doping in the polyacetylene sheet to obtain a conductive polymer lithium supplement. After the pre-lithiation is completed, the conductive polymer lithium supplement is ground into powder.

[0099] The method for preparing a lithium-ion battery provided in this embodiment comprises the following steps:

[0100] S1. Preparation of positive electrode sheet:

[0101] Since the amount of conductive polymer lithium supplement is relatively small and has little effect on the battery's energy density, the ratio of conductive agent to binder is not reduced. Lithium iron phosphate, SP, carbon nanotubes, and PVDF are slurried in a mass ratio of 96.5:1:0.5:2. First, PVDF and NMP are combined to prepare a glue solution. The conductive polymer lithium supplement is then added to the glue solution and dispersed at high speed. SP and carbon nanotubes are then added in sequence and dispersed at high speed. Finally, lithium iron phosphate is added and dispersed at high speed to complete the slurry. The slurry is coated, rolled, and die-cut to produce the positive electrode sheet.

[0102] S2. Preparation of lithium-ion batteries:

[0103] The positive electrode and negative electrode sheets prepared in step S1 and the 9 μm polypropylene separator were stacked to obtain a battery cell, and then the electrolyte was injected and assembled to obtain a lithium-ion battery. The electrolyte used was 1 mol / L LiPF6 / EC+EMC+DMC (volume ratio of 1:1:1) electrolyte.

[0104] The first coulombic efficiency of the lithium-ion battery provided in this embodiment is 96%.

[0105] Figure 2 This is the first charge and discharge curve of the battery in Example 1. Figure 3 This is the first charge and discharge curve of the battery in Comparative Example 1, as shown in Figure 2 and Figure 3 As shown, the first coulombic efficiency of the battery's electrochemical performance increased from the initial 90% to 96%, indicating that the conductive polymer lithium replenisher successfully replenished lithium.

[0106] Comparative Example 2

[0107] The design capacity of the lithium-ion battery provided in this comparative example is 50 Ah.

[0108] The method for preparing a lithium-ion battery provided in this comparative example comprises the following steps:

[0109] S1. Preparation of negative electrode sheet:

[0110] Silicon-carbon graphite, SP, CMC, and SBR were slurried in a mass ratio of 95:1.8:1.2:2. First, dry-mix the silicon-carbon graphite, CMC, and SP. Then, water was added and kneaded. After kneading, an appropriate amount of water was added for high-speed dispersion. Finally, SBR was added to complete the slurry. The slurry was then coated, rolled, and die-cut to produce the negative electrode sheet.

[0111] S2. Preparation of lithium-ion batteries:

[0112] The positive electrode sheet, the negative electrode sheet prepared in step S1, and a 9μm polypropylene separator were stacked to obtain a battery cell, and then the electrolyte was injected and assembled to obtain a lithium-ion battery. The electrolyte used was 1 mol / L LiPF6 / EC+EMC+DMC (volume ratio of 1:1:1) electrolyte.

[0113] The lithium ion battery prepared in this comparative example has an initial coulombic efficiency of 86%, and a capacity retention rate of 60% after 10,000 cycles.

[0114] Example 2

[0115] The purpose of this embodiment is to improve the initial coulombic efficiency and cycle performance of the lithium-ion battery prepared in Comparative Example 2. In this embodiment, the conductive polymer is used as the negative electrode lithium replenisher, and the negative electrode active material is silicon carbon graphite. The lithium replenisher is used as the negative electrode lithium replenisher to improve the initial coulombic efficiency and long cycle performance of the battery. The design capacity of the battery is 50Ah, the expected initial efficiency is CE2 = 95%, and the actual initial efficiency is CE1 = 86%; the actual capacity retention rate after 10,000 cycles is 60%, and the expected capacity retention rate is 80%. The theoretical lithium replenishment amount of the battery is M li =3.756g. The doping concentration of the conductive polymer σ = 30%, and the mass of the conductive polymer m is calculated to be 8.764g.

[0116] The preparation method of the conductive polymer lithium supplement provided in this embodiment comprises the following steps:

[0117] S1, weigh 8.764g of polypyrrole (conductivity 10 -6 S / cm), placed in a circular tablet press slot, and pressed into an area of ​​40cm 2 The polypyrrole sheet is 1.8 mm thick and weighs 2.5 g of round lithium sheets, with a mass of 2.5 g each. The area of ​​the lithium sheet is 40 cm 2 , two lithium sheets are sandwiched between the two ends of the above-mentioned polypyrrole sheet.

[0118] S2, referring to step S2 of Example 1, clamp the stainless steel metal collector plate between the two ends of the lithium sheet, and apply a force of 40N to press the metal collector plate, referring to Figure 1 The circuit diagram is shown in Figure 1. Pre-lithiation is performed to achieve lithium doping in the polypyrrole sheet to obtain a conductive polymer lithium supplement. Pre-lithiation process steps: Step 1: 40mA / cm 2 The constant current pre-lithiation time is 3h; the second step: 30mA / cm 2 The constant current pre-lithiation time is 4h; the third step: 20mA / cm 2 The constant current pre-lithiation time is 4h; the fourth step: 10mA / cm 2The constant current pre-lithiation time is 5h. After the pre-lithiation is completed, the actual pre-lithiation capacity of the conductive polymer is 14.8Ah, and the pre-lithiation amount is M li =3.83g, which can be ground into powder to prepare a conductive polymer lithium supplement.

[0119] The method for preparing a lithium-ion battery provided in this embodiment comprises the following steps:

[0120] S1. Preparation of negative electrode sheet:

[0121] Since the amount of conductive polymer lithium supplement is relatively large, it affects the energy density of the battery, so the amount of conductive agent and binder is reduced. In Comparative Example 2, the mass ratio of silicon carbon graphite, SP, CMC and SBR is 95:1.8:1.2:2. In this embodiment (after adding the lithium supplement), the mass ratio of silicon carbon graphite, SP, CMC, SBR and lithium supplement is 95:1.8-x:1.2:2-y:x+y, which reduces the proportion of SP and SBR. The amount of SP is reduced by 5.134g, and the amount of SBR is reduced by 7.46g. First, the silicon carbon graphite, CMC, SP and conductive polymer lithium supplement are dry-mixed together, and then water is added for kneading. After kneading, an appropriate amount of water is added for high-speed dispersion, and finally SBR is added to complete the slurrying. The slurry is coated, rolled and die-cut to prepare the negative electrode sheet. The amount of silicon carbon graphite in this embodiment is the same as that in Comparative Example 2.

[0122] S2. Preparation of lithium-ion batteries:

[0123] The positive electrode sheet, the negative electrode sheet prepared in step S1, and a 9μm polypropylene separator were stacked to obtain a battery cell, and then the electrolyte was injected and assembled to obtain a lithium-ion battery. The electrolyte used was 1 mol / L LiPF6 / EC+EMC+DMC (volume ratio of 1:1:1) electrolyte.

[0124] The initial coulombic efficiency of the lithium-ion battery prepared in this example is 95%, and the capacity retention rate after 10,000 cycles is 82%, which indicates that the conductive polymer lithium replenisher can effectively replenish lithium.

[0125] Comparative Example 3

[0126] This comparative example is the same as Example 2, except that a lithium-copper composite strip containing the same mass of lithium as in Example 2 is used as a lithium source, and an electrochemical pre-lithiation method is used. After the battery is assembled, it needs to be left at high temperature for 3 days to allow the lithium ions and the negative electrode material to react for pre-lithiation. This method is only suitable for negative electrode pre-lithiation. Its electrochemical performance shows that the first coulombic efficiency of the lithium-ion battery is increased from 86% to 91%. From this, it can be concluded that even if the amount of lithium replenishment is sufficient, the low reaction kinetics of electrochemical pre-lithiation is not enough to allow sufficient lithium to react with the negative electrode material, and in the subsequent long cycle process, the remaining lithium no longer participates in the reaction, so the capacity retention rate after 10,000 cycles is still only 61%, which is not much improved. This shows that the amount of lithium replenishment using the lithium replenishment method provided in Comparative Example 3 is limited.

[0127] Comparative Example 4

[0128] This comparative example is basically the same as Example 2, except that inert lithium powder is used as the lithium supplement agent for slurry mixing, silicon carbon graphite is used in the proportion, and the mass ratio of SP, CMC, SBR and inert lithium powder is 95:1.8-x:1.2:2-y:x+y (the values ​​of x and y are the same as those in Example 2), wherein the weight of the inert lithium powder is the same as the weight of the lithium supplement agent in Example 2. This comparative example mainly illustrates the physical properties of the conductive polymer lithium supplement agent.

[0129] The peel strength and resistance of the electrode sheets prepared in Example 2, Comparative Examples 2, and Comparative Examples 4 were tested. The peel strength and membrane resistance of the negative electrode sheet in Comparative Example 2 were 5 N / m and 1.72 mΩ, respectively. The peel strength and membrane resistance of the negative electrode sheet in Example 2 were 5.1 N / m and 1.70 mΩ, respectively. The peel strength and membrane resistance of Comparative Example 4 were 4.7 N / m and 1.90 mΩ. In Example 2, the use of a lithium supplement to replace part of the binder and conductive agent had little effect on the peel strength and conductivity of the electrode sheet. However, in Comparative Example 4, the use of inert lithium powder to replace part of the binder and conductive agent significantly reduced the peel strength and conductivity of the electrode sheet. This indicates that the lithium supplement provided by the present application can achieve the desired lithium supplementation effect without significantly reducing the peel strength and conductivity of the electrode sheet. It can also replace part of the binder and conductive agent, reducing the binder content and conductive agent content in both the positive and negative electrodes, thereby reducing the impact of the lithium supplement on battery weight, increasing the proportion of active material, and achieving a higher energy density.

[0130] Conventional lithium replenishment methods (including electrochemical pre-lithiation, lithium powder and other commonly used pre-lithiation methods) will affect the energy density of the battery to a certain extent as the amount of lithium replenishment increases. Compared with conventional lithium replenishment methods, the lithium replenisher of the present application can increase the energy density of the battery without affecting the battery manufacturing process.

[0131] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A method for preparing a lithium supplement, comprising the following steps: S1, first pressing the conductive polymer into a sheet, and then placing the lithium source on the conductive polymer sheet; S2, connecting the conductive polymer sheet to the negative electrode of an external power source, connecting the lithium source to the positive electrode of the external power source, applying current to the conductive polymer sheet and the lithium source to complete lithium doping, and obtaining the lithium supplement; The lithium supplement comprises a conductive polymer and lithium doped in the conductive polymer, wherein the conductivity of the conductive polymer is 10 -9 -10 3 S / cm; The lithium source is lithium metal sheet, lithium copper composite belt or lithium powder; Taking the total mass of the lithium supplement agent as 100%, the mass percentage of the lithium is 1%-50%.

2. The method for preparing a lithium supplement according to claim 1, wherein: During the process of pressing the conductive polymer into a sheet, the pressure is 0.01-0.5 tons; and / or, the thickness of the conductive polymer sheet is 0.1-100 mm; And / or, the lithium source is disposed on both sides of the conductive polymer sheet; And / or, in step S2, the current density is 10-1000 mA / cm 2 ; and / or, in step S2, the current density of the doping process decreases as the lithium ion doping concentration increases; And / or, the conductive polymer includes at least one of polyacetylene, polypyrrole, polythiophene, polyaniline, polyparaphenylene, and polyparaphenylene vinylene.

3. The method for preparing a lithium supplement according to claim 1, wherein: In step S2 , the lithium source is in contact with a metal current collector plate, so that the lithium source is connected to the positive electrode of an external power source through the metal current collector plate.

4. The method for preparing a lithium supplement according to claim 3, wherein: The metal current collector plate is a stainless steel plate, a copper plate or an aluminum alloy plate; And / or, in step S2, a force of 0-1000 N but not 0 N is applied to the metal current collector plate to ensure close contact between the metal current collector plate and the lithium source.

5. The method for preparing a lithium supplement according to claim 1, wherein: In step S2, the lithium-doped conductive polymer is ground into powder to obtain the lithium supplement agent.

6. A lithium-ion battery comprising a positive electrode sheet and a negative electrode sheet, characterized in that: The active material on the positive electrode plate includes positive electrode active material A and a lithium supplement agent prepared by the preparation method according to any one of claims 1 to 5; and / or, the active material on the negative electrode plate includes negative electrode active material B and a lithium supplement agent prepared by the preparation method according to any one of claims 1 to 5.

7. The lithium-ion battery according to claim 6, characterized in that The amount of the lithium supplement agent is determined by the pre-lithium amount, which is the sum of the pre-lithium amount and the mass of the conductive polymer; And / or, the positive electrode active material A includes at least one of lithium iron phosphate, lithium cobalt phosphate, lithium manganese iron phosphate, and a ternary material; And / or, the negative electrode active material B includes at least one of graphite, silicon-oxygen negative electrode, silicon-oxygen-graphite negative electrode, and silicon-carbon-graphite.

8. The lithium-ion battery according to claim 7, characterized in that The calculation formula of the pre-lithium amount is selected from at least one of the following: M Li =(CE1-CE0)*A1 / C Li (1), A1 is the design capacity of the battery, CE1 is the design first coulombic efficiency of the battery, CE0 is the actual first coulombic efficiency of the battery, M Li is the mass of lithium required, C Li is the theoretical specific capacity of lithium; M Li = (A0(σ1-σ2)) / C Li (2), A0 is the design capacity of the battery, σ1 is the capacity retention rate after theoretical N cycles, σ2 is the capacity retention rate after actual N cycles, M Li is the mass of lithium required, C Li is the theoretical specific capacity of lithium.

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