CN112652754A - Positive electrode and preparation method and application thereof - Google Patents

Positive electrode and preparation method and application thereof Download PDF

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Publication number
CN112652754A
CN112652754A CN202011598489.9A CN202011598489A CN112652754A CN 112652754 A CN112652754 A CN 112652754A CN 202011598489 A CN202011598489 A CN 202011598489A CN 112652754 A CN112652754 A CN 112652754A
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positive electrode
active material
material layer
porous metal
electrode active
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苏树发
其他发明人请求不公开姓名
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Svolt Energy Technology Co Ltd
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Svolt Energy Technology Co Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/04—Processes of manufacture in general
    • H01M4/0402—Methods of deposition of the material
    • H01M4/0404—Methods of deposition of the material by coating on electrode collectors
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/04—Processes of manufacture in general
    • H01M4/0402—Methods of deposition of the material
    • H01M4/0416—Methods of deposition of the material involving impregnation with a solution, dispersion, paste or dry powder
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/134—Electrodes based on metals, Si or alloys
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/386—Silicon or alloys based on silicon
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Abstract

The invention discloses a positive electrode and a preparation method and application thereof, wherein the positive electrode comprises the following components: the cathode structure comprises a cathode current collector, a first cathode active material layer, a porous metal layer and a second cathode active material layer, wherein the first cathode active material layer is formed on the surface of the cathode current collector; the porous metal layer is formed on the surface of the first positive electrode active material layer; the second positive electrode active material layer is formed on the surface of the porous metal layer. By adopting the anode, the lithium part in the anode can be stored in a lithium metal alloy form under the condition of effectively controlling the unit area capacity of the anode not to be higher than the unit area capacity of the cathode, so that the energy density of a battery cell is effectively improved (from 180-230 wh/kg to 230-280 wh/kg) under the condition of maintaining the application and process level of the existing mature chemical system, mature base material and diaphragm, and the electrical property, reliability and safety performance are ensured to meet the requirements of the existing power battery cell.

Description

Positive electrode and preparation method and application thereof
Technical Field
The invention belongs to the field of batteries, and particularly relates to a positive electrode and a preparation method and application thereof.
Background
With the development of electric vehicles, the requirements on the energy density (at present, the normal level is 180-230 wh/kg) of a power battery are higher and higher. As a core component of the electric vehicle, the energy density of the power battery influences the design of the whole vehicle, including the control of the performance and the cost of the whole vehicle, the high-energy-density power battery can effectively control the weight of the whole vehicle and the design of other parts, in addition, the cost of the power battery in the electric vehicle is nearly 50%, the energy density of the power battery is improved, the cost of non-energy units such as mechanical parts and the like can be reduced, and the cost of the whole vehicle is effectively controlled.
The method for improving the energy density of the power battery at present comprises the following three methods:
(1) negative electrode side: the high Ni system improves the capacity exertion of the unit weight of the negative electrode by improving the Ni content in the negative electrode material, and the current battery core level technical state and level is 240-280 wh/kg; the high-voltage system improves the capacity exertion of the negative electrode per unit weight by improving the upper limit voltage in the charging process of the negative electrode material, and the current battery cell level technical state and level are 230-260 wh/kg;
(2) in the aspect of a positive electrode: alloy doping by adding Si/SiO2The alloy is used for improving the capacity exertion of the unit weight of the anode, and the current battery cell level technical state and level are 250-350 wh/kg;
(3) the process aspect is as follows: by increasing the coating weight of the anode and the cathode and reducing the thickness of a base material (aluminum foil and copper foil) and a diaphragm, the effective capacity exertion of unit weight is improved, and the current battery core level technical state and level are 230-270 wh/kg.
However, the above-mentioned technology for increasing the energy density of the power battery has the following disadvantages:
(1) negative electrode side: the high Ni system, the increase of Ni content reduces the potential of negative pole oxygen evolution, thereby bringing about the risk of high gas production of the battery cell, which will deteriorate the long-term reliability of the battery cell, such as cycle life, storage life and battery cell expansion control, and meanwhile, the higher Ni content reduces the temperature threshold of the negative pole material for thermal runaway, which will deteriorate the safety of the battery cell under related application, such as high temperature, overcharge, extrusion and the like; in a high-voltage system, the oxidation of the charging terminal negative electrode is improved due to the increase of the upper limit service voltage of the negative electrode, and the oxidation of the charging terminal negative electrode to an electrolyte and a diaphragm is accelerated, so that gas generation is deteriorated, and adverse effects are brought to long-term reliability;
(2) in the aspect of a positive electrode: alloy doping, addition of Si/SiO2The battery core has very large shrinkage and expansion in the charging and discharging processes, and the anode has the phenomena of demoulding and powder falling under a high shrinkage and expansion ratio along with the circulation, and meanwhile, the stability and the integrity of an SEI film on the surface of the anode are influenced, so that the long-term service life and the capacity maintenance of the battery core are greatly deteriorated;
(3) the process aspect is as follows: the increase of coating weight of the positive electrode and the negative electrode deteriorates the power, the charging window and the long-term cycle life of the battery core, and brings great challenges to the process and equipment; the reduction of the base material (aluminum foil and copper foil) mainly affects the process manufacturing, the thin base material is easy to break in the manufacturing process of the battery cell, and the excellent rate of the battery cell manufacturing process is seriously affected, so that the cost is increased; the diaphragm is used as a part for separating the direct contact short circuit of the positive electrode and the negative electrode, the thickness of the diaphragm is important for controlling the safety of the short circuit in the battery cell, and the safety risk of the short circuit in the battery cell caused by the thickness reduction is reduced.
Therefore, the existing technology for improving the energy density of the power battery needs to be explored.
Disclosure of Invention
The present invention is directed to solving, at least to some extent, one of the technical problems in the related art. Therefore, the invention aims to provide a positive electrode and a preparation method and application thereof, and lithium in the positive electrode can be stored in a lithium metal alloy form under the condition of effectively controlling the unit area capacity of the positive electrode not to be higher than that of the negative electrode, so that the energy density of a battery cell is effectively improved (from 180-230 wh/kg to 230-280 wh/kg) under the condition of maintaining the application and process level of the existing mature chemical system, mature base material and diaphragm, and the electrical property, reliability and safety performance are ensured to meet the requirements of the existing power battery cell.
In one aspect of the invention, a positive electrode is provided. According to an embodiment of the present invention, the positive electrode includes:
a positive current collector;
a first positive electrode active material layer formed on the surface of the positive electrode current collector;
a porous metal layer formed on a surface of the first positive electrode active material layer;
a second positive electrode active material layer formed on a surface of the porous metal layer.
According to the positive electrode of the embodiment of the invention, the porous metal layer is arranged between the first positive electrode active material layer and the second positive electrode active material layer, so that the capacity per unit area of the positive electrode is not higher than that of the negative electrode of the existing lithium ion battery, namely, the ratio of the capacity per unit area of the positive electrode to the capacity per unit area of the negative electrode in the lithium ion battery loaded with the positive electrode is not higher than 1, the porous metal in the porous metal layer is easy to react with lithium to form an alloy, during the charging process, lithium ions reach the porous metal layer through the second positive electrode active material layer far away from the positive electrode current collector, part of the lithium ions react with the porous metal to form a lithium metal alloy, the other part of the lithium ions migrate to the first positive electrode active material layer through holes of the porous metal and complete intercalation, and the potential formed by the lithium metal alloy is higher than the intercalation potential of the first positive electrode active material layer, therefore, a large amount of lithium ions exist in the form of lithium metal alloy and are distributed along the growth of the porous metal, so that the position and the shape of the lithium metal alloy on the positive electrode when the ratio of the unit area capacity of the positive electrode to the unit area capacity of the negative electrode is not higher than 1 can be effectively controlled, and the safety problem caused by puncturing a diaphragm due to the fact that irregular sharp-knife-shaped lithium dendrites are deposited on the positive electrode is avoided; on the other hand, the energy density of the lithium metal alloy is far higher than that of LiC6This will greatly increase the energy density of the cell. Therefore, by adopting the anode, the lithium part in the anode can be stored in a lithium metal alloy form under the condition of effectively controlling the unit area capacity of the anode not to be higher than that of the cathode, so that the energy density of a battery cell (from the present) is effectively improved under the condition of maintaining the application and process level of the conventional mature chemical system, mature base material and diaphragmThe power battery core is improved to 230-280 wh/kg from 180-230 wh/kg, and the electrical property, reliability and safety performance of the power battery core can meet the requirements of the current power battery core.
In addition, the positive electrode according to the above embodiment of the present invention may further have the following additional technical features:
in some embodiments of the present invention, the pore shape of the porous metal layer is a circle or a polygon. Thereby, the cell energy density can be improved.
In some embodiments of the present invention, the size of the holes is 0.1-10 mm. This can prevent the strength of the positive electrode while ensuring smooth migration of lithium ions in the electrolyte to the first positive electrode active material layer.
In some embodiments of the present invention, the gap between two adjacent holes is 0.5-30 mm. This can prevent the strength of the positive electrode while ensuring smooth migration of lithium ions in the electrolyte to the first positive electrode active material layer.
In some embodiments of the present invention, the first positive electrode active material layer and the second positive electrode active material layer independently include a graphite material and Si — SiO, respectively2At least one of the alloy materials.
In some embodiments of the present invention, the positive electrode includes a plurality of the porous metal layers, the first positive electrode active material layer or the second positive electrode active material layer is disposed between adjacent ones of the porous metal layers, and the first positive electrode active material layer or the second positive electrode active material layer is disposed farthest on the positive electrode current collector.
In some embodiments of the present invention, the first positive electrode active material layer or the second positive electrode active material layer corresponding to the farthest end on the positive electrode current collector accounts for 5 to 95% of the total mass of the positive electrode.
In some embodiments of the present invention, the thickness of the porous metal layer is 2 to 20 μm. Therefore, the tearing of the positive electrode can be avoided while the cell energy density is ensured.
In some embodiments of the invention, the porous metal layer comprises at least one of metallic aluminum, metallic tin, an aluminum-tin alloy, an aluminum-copper alloy, and an aluminum-copper-iron alloy.
In a second aspect of the invention, the invention provides a method of preparing the above-described positive electrode. According to an embodiment of the invention, the method comprises:
(1) mixing a first positive electrode active material, a binder, a conductive agent, and a thickener to obtain a first positive electrode slurry;
(2) applying the first positive electrode slurry on a positive electrode current collector surface to form a first positive electrode active material layer on the positive electrode current collector surface;
(3) applying a porous metal on the first positive electrode active material layer to form a porous metal layer on a surface of the first positive electrode active material layer;
(4) mixing a second positive electrode active material, a binder, a conductive agent, and a thickener to obtain a second positive electrode slurry;
(5) the second positive electrode slurry is applied on the surface of the porous metal layer to obtain a positive electrode.
According to the method of manufacturing the above-described positive electrode of the embodiment of the invention, the first positive electrode active material layer is formed on the surface of the positive electrode current collector by applying the first positive electrode slurry including the first positive electrode active material, the binder, the conductive agent, and the thickener on the surface of the positive electrode current collector, and then the porous metal is applied on the first positive electrode active material layer so that the porous metal layer is formed on the surface of the first positive electrode active material layer; and finally, applying second anode slurry comprising a second anode active material, a binder, a conductive agent and a thickening agent on the surface of the porous metal layer to form a second anode active material layer on the surface of the porous metal layer, namely, arranging the porous metal layer between the first anode active material layer and the second anode active material layer to ensure that the capacity per unit area of the anode is not higher than that of the cathode of the conventional lithium ion battery, namely, the ratio of the capacity per unit area of the anode to the capacity per unit area of the cathode in the lithium ion battery loaded with the anode is not higher than 1, the porous metal in the porous metal layer is easy to react with lithium to form an alloy, and in the charging process, lithium ions pass through the second anode active material layer far away from the anode current collectorThe positive active material layer reaches the porous metal layer, part of lithium ions react with the porous metal to generate a lithium metal alloy, the other part of lithium ions migrate to the first positive active material layer through holes of the porous metal and complete intercalation, and because the potential formed by the lithium metal alloy is higher than the intercalation potential of the first positive active material layer, a large number of lithium ions exist in the form of the lithium metal alloy and are distributed along the growth of the porous metal, so that the position and the shape of the lithium metal alloy on the positive electrode when the ratio of the unit area capacity of the positive electrode to the unit area capacity of the negative electrode is not higher than 1 can be effectively controlled, and on one hand, the safety problem caused by puncturing a diaphragm due to the fact that irregular sharp-knife-shaped lithium dendrites are generated on the positive electrode in a deposition mode; on the other hand, the energy density of the lithium metal alloy is far higher than that of LiC6This will greatly increase the energy density of the cell. Therefore, the positive electrode obtained by the method can store lithium in the positive electrode in a lithium metal alloy form under the condition of effectively controlling the unit area capacity of the positive electrode not to be higher than the unit area capacity of the negative electrode, so that the energy density of the battery cell is effectively improved (from 180-230 wh/kg to 230-280 wh/kg) under the condition of maintaining the application and process level of the existing mature chemical system, mature base materials and diaphragms, and the requirements of the current power battery cell on electrical property, reliability and safety performance are met.
In a third aspect of the present invention, a lithium ion battery is presented. According to an embodiment of the present invention, the lithium ion battery includes a positive electrode, a negative electrode, an electrolyte and a separator, the positive electrode is the positive electrode or the positive electrode obtained by the method, wherein a ratio of a capacity per unit area of the positive electrode to a capacity per unit area of the negative electrode is not higher than 1, and preferably 0.4 to 0.7. Therefore, by loading the positive electrode with higher energy density and safety performance, the lithium ion battery has excellent energy density, electrical performance, reliability and safety performance, thereby meeting the requirements of the current power battery core.
In some embodiments of the invention, the anode comprises a metal oxide material having the formula LiNixCoyMnzFeaAlbPcO2Wherein x is more than or equal to 0 and less than or equal to 1, y is more than or equal to 0 and less than or equal to 1, z is more than or equal to 0 and less than or equal to 1, a is more than or equal to 0 and less than or equal to 1, b is more than or equal to 0 and less than or equal to 0.8, and c is more than or equal to 0.
In a fourth aspect of the present invention, a vehicle is presented. According to an embodiment of the present invention, the vehicle includes the lithium ion battery described above. Therefore, by loading the lithium ion battery with excellent energy density, electrical property, reliability and safety performance, the vehicle has excellent driving range and lower overall cost.
Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Drawings
The above and/or additional aspects and advantages of the present invention will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:
fig. 1 is a schematic structural view of a positive electrode according to an embodiment of the present invention;
fig. 2 is a schematic flow chart of a method for preparing the above-described positive electrode according to still another embodiment of the present invention.
Detailed Description
The following detailed description of the embodiments of the present invention is intended to be illustrative, and not to be construed as limiting the invention.
In one aspect of the invention, a positive electrode is provided. According to an embodiment of the present invention, referring to fig. 1, the positive electrode includes a positive electrode collector 100, a first positive electrode active material layer 200, a porous metal layer 300, and a second positive electrode active material layer 400.
According to the embodiment of the present invention, a person skilled in the art can select a material of the positive current collector 100 according to actual needs, for example, the positive current collector 100 is a copper foil current collector.
According to an embodiment of the present invention, referring to fig. 1, a first positive active material layer 200 is formed on a surface of a positive current collector 100, and the first positive active material layer 200 includes a material that can perform lithium intercalation and deintercalation, for example, including a graphite material and Si — SiO2Alloy materialWherein the graphite material comprises at least one of natural graphite, artificial graphite, soft carbon, and hard carbon. It should be noted that, a person skilled in the art can select the thickness of the first positive electrode active material layer 200 according to actual needs, and details are not described here.
According to an embodiment of the present invention, referring to fig. 1, a porous metal layer 300 is formed on a surface of the first cathode active material layer 200, and the porous metal layer 300 includes a metal that is easily alloyed with lithium, for example, includes at least one of metallic aluminum, metallic tin, an aluminum-tin alloy, an aluminum-copper alloy, and an aluminum-copper-iron alloy. The inventors found that by disposing a porous metal layer on the surface of the first cathode active material layer, the capacity per unit area of the cathode is not higher than that of the cathode of the existing lithium ion battery, that is, the ratio of the capacity per unit area of the cathode to the capacity per unit area of the cathode in the lithium ion battery loaded with the cathode is not higher than 1.
Further, those skilled in the art can select the shape of the holes of the porous metal layer 300 according to actual needs, for example, the holes may be circular or polygonal, where the polygonal includes a triangle, a quadrangle, a pentagon, or the like; and the size of the holes is 0.1-10 mm. The inventors found that if the pore size is too small, the wetting of the electrolyte into the first positive electrode active material layer and the migration of lithium ions are affected, and if the pore size is too large, the strength of the positive electrode is affected, resulting in easy breakage. Meanwhile, the gap between two adjacent holes is 0.5-30 mm. The inventor finds that the gap between two adjacent holes is too large, which affects the strength of the positive electrode and causes the positive electrode to be easy to break, and if the gap between two adjacent holes is too small, the infiltration of the electrolyte into the first positive electrode active material layer and the migration of lithium ions are affected. It should be noted that the shape of the holes in the porous metal layer 300 may be one or a combination of more.
According to an embodiment of the present invention, referring to fig. 1, a second cathode active material layer 400 is formed on a surface of the porous metal layer 300, and the second cathode active material layer 400 includes a material that can perform lithium intercalation and deintercalation, for example, including a graphite material and Si — SiO2At least one of alloy materials, wherein the graphite materialIncluding at least one of natural graphite, artificial graphite, soft carbon, and hard carbon. The thickness of the second positive electrode active material layer 400 can be selected by those skilled in the art according to actual needs, and the composition of the second positive electrode active material layer 400 may be the same as or different from that of the first positive electrode active material layer 200, and the size and shape of the active material particles in the first positive electrode active material layer 200 and the second positive electrode active material layer 400 may be the same or different.
The inventors have found that by disposing a porous metal layer between a first positive electrode active material layer and a second positive electrode active material layer so that the capacity per unit area of the positive electrode is not higher than that of a negative electrode of an existing lithium ion battery, i.e., the ratio of the capacity per unit area of the positive electrode to that of the negative electrode in the lithium ion battery loaded with the positive electrode is not higher than 1, the porous metal in the porous metal layer is easily alloyed with lithium, during charging, lithium ions reach the porous metal layer through the second positive electrode active material layer away from a positive electrode current collector, part of the lithium ions react with the porous metal to form a lithium metal alloy, and the other part of the lithium ions migrate to the first positive electrode active material layer through pores of the porous metal to complete intercalation, and since the lithium metal alloy formation potential is higher than the intercalation potential at the first positive electrode active material layer, a large amount of lithium ions will exist in the form of the lithium metal alloy, the lithium metal alloy is arranged along the porous metal growth, so that the position and the shape of the lithium metal alloy on the positive electrode when the ratio of the unit area capacity of the positive electrode to the unit area capacity of the negative electrode is not higher than 1 can be effectively controlled, and the safety problem caused by puncturing a diaphragm due to the fact that irregular sharp knife-shaped lithium dendrites are generated on the positive electrode in a deposition mode is avoided; on the other hand, the energy density of the lithium metal alloy is far higher than that of LiC6This will greatly increase the energy density of the cell. Therefore, by adopting the anode, the lithium part in the anode can be stored in a lithium metal alloy form under the condition of effectively controlling the unit area capacity of the anode not to be higher than that of the cathode, so that the energy density of a battery cell is effectively improved (improved from the existing 180-230 wh/kg) under the condition of maintaining the application and process level of the existing mature chemical system, mature base material and diaphragm230-280 wh/kg) and ensures that the electrical property, the reliability and the safety performance meet the requirements of the current power battery cell.
Further, the positive electrode includes a plurality of porous metal layers 300, and the first positive electrode active material layer 200 or the second positive electrode active material layer 400 is disposed between the adjacent porous metal layers 300, and the first positive electrode active material layer 200 or the second positive electrode active material layer 400 is disposed at the farthest end on the positive electrode collector 100, wherein the active materials in the first positive electrode active material layers 200 of different layers may be one type or different types, and the active materials in the second positive electrode active material layers 400 of different layers may be one type or different types. In addition, the holes in the porous metal layers 300 of different layers may be the same or different, and those skilled in the art can select the holes according to actual needs.
Preferably, the thickness of the single porous metal layer 300 is 2 to 20 μm. The inventor finds that if the thickness of the porous metal layer 300 is too small, the porous metal layer 300 is easy to break, the manufacturing yield is low, and the cost is high, while if the thickness of the porous metal layer 300 is too high, the occupied positive electrode space is too much, the overall space utilization rate of the battery cell is reduced, and the energy density is correspondingly reduced. It should be noted that, unless otherwise specified, the thickness of the porous metal layer 300 refers to the thickness of a single porous metal layer on one side of the positive current collector 100.
Further, the first positive electrode active material layer 200 or the second positive electrode active material layer 400 corresponding to the farthest end on the positive electrode current collector 300 accounts for 5-95% of the total mass of the positive electrode. It should be noted that the term "farthest end on the positive electrode current collector 300" may be understood as an end of the positive electrode current collector 300 farthest from the positive electrode current collector 300, that is, an outermost end thereof, and if the end of the positive electrode current collector 300 corresponding to the outermost end is the first positive electrode active material layer 200, it is understood herein that the first positive electrode active material layer 200 corresponding to the farthest end on the positive electrode current collector 100 accounts for 5 to 95% of the total mass of the positive electrode, and if the end of the positive electrode current collector 300 corresponding to the outermost end is the second positive electrode active material layer 400, it is understood herein that the second positive electrode active material layer 200 corresponding to the farthest end on the positive electrode current collector 100 accounts for 5 to 95% of the total mass of the positive electrode.
It should be noted that fig. 1 of the present application only shows a case of single-side coating on the positive electrode current collector, and a person skilled in the art may select to perform single-side coating or double-side coating on the positive electrode current collector according to actual needs.
In a second aspect of the invention, the invention provides a method of preparing the above-described positive electrode. According to an embodiment of the invention, referring to fig. 2, the method comprises:
s100: mixing a first positive electrode active material, a binder, a conductive agent, and a thickener
In this step, the first positive electrode active material, the binder, the conductive agent, and the thickener are mixed to obtain a first positive electrode slurry. Specifically, the first positive electrode active material includes a material capable of lithium intercalation and deintercalation, and includes, for example, a graphite material and Si-SiO2At least one of alloy materials, wherein the graphite material includes at least one of natural graphite, artificial graphite, soft carbon, and hard carbon.
It should be noted that the binder, the conductive agent and the thickener in this step are all materials conventionally used in the process of preparing the positive electrode in this field, and those skilled in the art can use these materials according to actual needs, and are not described herein again.
S200: applying a first positive electrode slurry on a surface of a positive electrode current collector
In this step, the first positive electrode slurry obtained as described above is applied onto the surface of the positive electrode current collector to form a first positive electrode active material layer on the surface of the positive electrode current collector. Specifically, coating of a first positive electrode slurry on the surface of a positive electrode current collector is completed by adopting a gravure, micro-gravure or transfer coating mode, and then the coated positive electrode current collector is dried, so that the first positive electrode slurry is solidified, and a first positive electrode active material layer is formed on the surface of the positive electrode current collector. It should be noted that, a person skilled in the art can select the thickness of the first positive electrode active material layer according to actual needs, and details are not described here.
S300: applying a porous metal on the first positive electrode active material layer
In this step, a porous metal is rolled on the first positive electrode active material layer to form a porous metal layer on the surface of the first positive electrode active material layer. The porous metal includes a metal that is easily alloyed with lithium, and includes at least one of metallic aluminum, metallic tin, an aluminum-tin alloy, an aluminum-copper alloy, and an aluminum-copper-iron alloy.
S400: mixing the second positive electrode active material, the binder, the conductive agent and the thickener
In this step, the second positive electrode active material, the binder, the conductive agent, and the thickener are mixed to obtain a second positive electrode slurry. Specifically, the second positive electrode active material includes a material capable of lithium intercalation and deintercalation, and includes, for example, a graphite material and Si-SiO2At least one of alloy materials, wherein the graphite material includes at least one of natural graphite, artificial graphite, soft carbon, and hard carbon.
It should be noted that, the binder, the conductive agent, and the thickener in this step are all materials conventionally used in the process of preparing the positive electrode in this field, and those skilled in the art may use the same or different composition of the second positive electrode slurry as that of the first positive electrode slurry according to actual needs, and the size and shape of the active material particles in the first positive electrode slurry and the second positive electrode slurry may be the same or different, and are not described herein again.
S500: applying a second positive electrode slurry on the surface of the porous metal layer
In this step, the second positive electrode slurry obtained above is applied onto the surface of the porous metal layer, that is, the second positive electrode active material layer is formed on the surface of the porous metal layer, to obtain a positive electrode. Specifically, coating of the second anode slurry on the surface of the porous metal layer is completed by adopting a gravure, micro-gravure or transfer coating mode, and then the coated anode current collector is dried, so that the second anode slurry is solidified, and a second anode active material layer is formed on the surface of the porous metal layer. It should be noted that, a person skilled in the art can select the thickness of the second positive electrode active material layer according to actual needs, and details are not described here.
The inventors have found that the positive electrode active material is obtained by mixing a positive electrode active material containing a first positive electrode active material,Applying a first positive electrode slurry of a binder, a conductive agent, and a thickener on a surface of a positive electrode current collector so that a first positive electrode active material layer is formed on the surface of the positive electrode current collector, and then applying a porous metal on the first positive electrode active material layer so that a porous metal layer is formed on a surface of the first positive electrode active material layer; finally, second anode slurry comprising a second anode active material, a binder, a conductive agent and a thickening agent is applied on the surface of the porous metal layer, so that a second anode active material layer is formed on the surface of the porous metal layer, namely, the porous metal layer is arranged between the first anode active material layer and the second anode active material layer, so that the unit area capacity of the anode is not higher than that of the cathode of the conventional lithium ion battery, namely, the ratio of the unit area capacity of the anode to the unit area capacity of the cathode in the lithium ion battery loaded with the anode is not higher than 1, the porous metal in the porous metal layer is easy to react with lithium to form an alloy, in the charging process, lithium ions reach the porous metal layer through the second anode active material layer far away from an anode current collector, part of the lithium ions react with the porous metal to form the lithium metal alloy, and the other part of the lithium ions are transferred to the first anode active material layer through the migration holes of the porous metal, the intercalation is completed, and because the forming potential of the lithium metal alloy is higher than the intercalation potential of the first anode active material layer, a large number of lithium ions exist in the form of the lithium metal alloy and are distributed along the growth of the porous metal, so that the position and the shape of the lithium metal alloy on the anode can be effectively controlled when the ratio of the unit area capacity of the anode to the unit area capacity of the cathode is not higher than 1, and on one hand, the safety problem caused by puncturing a diaphragm due to the generation of irregular sharp-knife-shaped lithium dendrites deposited on the anode is avoided; on the other hand, the energy density of the lithium metal alloy is far higher than that of LiC6This will greatly increase the energy density of the cell. Therefore, the positive electrode obtained by the method can store lithium in the positive electrode in a lithium metal alloy form under the condition of effectively controlling the unit area capacity of the positive electrode not to be higher than that of the negative electrode, so that the energy density of a battery cell is effectively improved (from 180-230 wh/kg to 230-280 wh/kg in the prior art) under the condition of maintaining the application and process level of the prior mature chemical system, mature base material and diaphragm) And the electrical property, reliability and safety performance are ensured to meet the requirements of the current power battery cell. It should be noted that the features and advantages described above for the positive electrode also apply to the method for preparing the positive electrode, and are not described in detail here.
In a third aspect of the present invention, a lithium ion battery is presented. According to an embodiment of the present invention, the lithium ion battery includes a positive electrode, a negative electrode, an electrolyte and a separator, the positive electrode is the positive electrode or the positive electrode obtained by the method, wherein a ratio of a capacity per unit area of the positive electrode to a capacity per unit area of the negative electrode is not higher than 1, and preferably 0.4 to 0.7. Therefore, by loading the positive electrode with higher energy density and safety performance, the lithium ion battery has excellent energy density, electrical performance, reliability and safety performance, thereby meeting the requirements of the current power battery core. It should be noted that the features and advantages described above for the positive electrode and the preparation method thereof are also applicable to the lithium ion battery, and are not described herein again.
According to an embodiment of the present invention, the negative electrode of the lithium ion battery comprises a metal oxide material having a chemical formula of LiNixCoyMnzFeaAlbPcO2Wherein x is more than or equal to 0 and less than or equal to 1, y is more than or equal to 0 and less than or equal to 1, z is more than or equal to 0 and less than or equal to 1, a is more than or equal to 0 and less than or equal to 1, b is more than or equal to 0 and less than or equal to 0.8, c is more than or equal to 0 and less than or equal to 4, and the metal oxide material has; the separator is a material with high porosity and allowing lithium ions to freely pass through, such as one or more of PE, PP and non-woven fabric materials; the electrolyte solution contains a solvent, which is one or more of cyclic esters such as Propylene Carbonate (PC) and Ethylene Carbonate (EC) and linear esters such as diethyl carbonate (DEC), dimethyl carbonate (DMC) and methyl ethyl carbonate (EMC), and a lithium salt, which is LiPF that is effectively soluble in the above solvent6、LiClO4And LiBO2And the like.
In a fourth aspect of the present invention, a vehicle is presented. According to an embodiment of the present invention, the vehicle includes the lithium ion battery described above. Therefore, by loading the lithium ion battery with excellent energy density, electrical property, reliability and safety performance, the vehicle has excellent driving range and lower overall cost. It should be noted that the features and advantages described above for the lithium ion battery are also applicable to the vehicle, and are not described herein again.
The following embodiments of the present invention are described in detail, and it should be noted that the following embodiments are exemplary only, and are not to be construed as limiting the present invention. In addition, all reagents used in the following examples are commercially available or can be synthesized according to methods herein or known, and are readily available to those skilled in the art for reaction conditions not listed, if not explicitly stated.
Example 1
The method for preparing the positive electrode comprises the following steps:
(1) homogenizing graphite particles, SBR (styrene butadiene rubber), CMC (sodium carboxymethylcellulose) and SP (conductive carbon black) according to a weight ratio of 95:2.5:1.5:1, wherein water is added to control the solid content to be 45-55% and the viscosity to be 2000-4000 mpa · s, and stirring is finished to obtain first positive electrode slurry;
(2) uniformly coating the first positive electrode slurry on the surface of a copper foil base material with the thickness of 8 mu m, wherein the coating weight of the first positive electrode slurry on two sides is 123g/m2Forming a first positive electrode active material layer on the surface of the copper foil substrate;
(3) rolling a 6-micron circular porous metal aluminum foil on the surface of the first positive electrode active material layer to form a porous metal layer (with the pore size of 1mm and the gap between adjacent pores of 1mm) on the surface of the first positive electrode active material layer;
(4) coating first anode slurry on the surface of the porous metal layer, and controlling the coating weight of the double surfaces to be 123g/m2And forming a second positive electrode active material layer on the surface of the porous metal layer, and then drying, rolling, die cutting and punching to form the positive electrode piece (the second positive electrode active material layer accounts for 50% of the total mass of the positive electrode piece).
Method for preparing negative pole piece
Taking a metal oxide material LiNi0.5Co0.2Mn0.3O2Ternary material, according to NCM (LiNi)0.5Co0.2Mn0.3O2Homogenizing PVDF (polyvinylidene fluoride) and SP (conductive carbon black) according to a weight ratio of 95:3:2, adding NMP (N-methyl-2 pyrrolidone) to control the solid content of the negative electrode slurry to be 68-75 wt% and the viscosity to be 6000-10000 mpa & s, stirring, uniformly coating the negative electrode slurry on the surface of an aluminum foil base material with the thickness of 12 mu m, wherein the coating weight of the two surfaces of the aluminum foil base material is 480g/m2And then drying, rolling, die cutting and punching to obtain the negative pole piece (the ratio of the unit area capacity N of the positive pole piece to the unit area capacity P of the negative pole piece is 1.0).
Example 2
The method for preparing the positive electrode comprises the following steps: the double-sided coating weight of the first positive electrode slurry in forming the first positive electrode active material layer was 110g/m2The coating weight of the first positive electrode slurry on both sides in forming the second positive electrode active material layer was 110g/m2Otherwise, the second positive active material layer in the positive electrode sheet was obtained in the same manner as in example 1, and accounted for 50% of the total mass of the positive electrode sheet.
The method for preparing the negative electrode piece is the same as that in example 1, wherein the ratio of the capacity N of the positive electrode piece per unit area to the capacity P of the negative electrode piece per unit area is 0.9.
Example 3
The method for preparing the positive electrode comprises the following steps: the weight of the first positive electrode slurry applied on both sides when the first positive electrode active material layer was formed was 98g/m2The weight of the first positive electrode slurry applied on both sides when forming the second positive electrode active material layer was 98g/m2Otherwise, the second positive active material layer in the positive electrode sheet was obtained in the same manner as in example 1, and accounted for 50% of the total mass of the positive electrode sheet.
The method for preparing the negative electrode piece is the same as that in example 1, wherein the ratio of the capacity N of the positive electrode piece per unit area to the capacity P of the negative electrode piece per unit area is 0.8.
Example 4
The method for preparing the positive electrode comprises the following steps: the weight of the first positive electrode slurry applied on both sides when the first positive electrode active material layer was formed was 86g/m2The weight of the first positive electrode slurry applied on both sides when forming the second positive electrode active material layer was 86g/m2And othersThe second positive active material layer in the positive electrode sheet obtained in the same manner as in example 1 accounted for 50% of the total mass of the positive electrode sheet.
The method for preparing the negative electrode piece is the same as that in example 1, wherein the ratio of the capacity N of the positive electrode piece per unit area to the capacity P of the negative electrode piece per unit area is 0.7.
Example 5
The method for preparing the positive electrode comprises the following steps: the weight of the first positive electrode slurry applied on both sides when the first positive electrode active material layer was formed was 74g/m2The weight of the first positive electrode slurry applied on both sides when forming the second positive electrode active material layer was 74g/m2Otherwise, the second positive active material layer in the positive electrode sheet was obtained in the same manner as in example 1, and accounted for 50% of the total mass of the positive electrode sheet.
The method for preparing the negative electrode piece is the same as that in example 1, wherein the ratio of the capacity N of the positive electrode piece per unit area to the capacity P of the negative electrode piece per unit area is 0.6.
Example 6
The method for preparing the positive electrode comprises the following steps: the weight of the first positive electrode slurry applied on both sides when forming the first positive electrode active material layer was 61g/m2The weight of the first positive electrode slurry applied on both sides when forming the second positive electrode active material layer was 61g/m2Otherwise, the second positive active material layer in the positive electrode sheet was obtained in the same manner as in example 1, and accounted for 50% of the total mass of the positive electrode sheet.
The method for preparing the negative electrode plate is the same as that in example 1, wherein the ratio of the capacity N of the positive electrode plate per unit area to the capacity P of the negative electrode plate per unit area is 0.5.
Example 7
The method for preparing the positive electrode comprises the following steps: the double-sided coating weight of the first positive electrode slurry in forming the first positive electrode active material layer was 49g/m2The weight of the first positive electrode slurry applied on both sides when forming the second positive electrode active material layer was 49g/m2Otherwise, the second positive active material layer in the positive electrode sheet was obtained in the same manner as in example 1, and accounted for 50% of the total mass of the positive electrode sheet.
The method for preparing the negative electrode plate is the same as that in example 1, wherein the ratio of the capacity N of the positive electrode plate per unit area to the capacity P of the negative electrode plate per unit area is 0.4.
Example 8
The method for preparing the positive electrode comprises the following steps: the double-sided coating weight of the first positive electrode slurry in forming the first positive electrode active material layer was 37g/m2The coating weight of the first positive electrode slurry on both sides in forming the second positive electrode active material layer was 37g/m2Otherwise, the second positive active material layer in the positive electrode sheet was obtained in the same manner as in example 1, and accounted for 50% of the total mass of the positive electrode sheet.
The method for preparing the negative electrode plate is the same as that in example 1, wherein the ratio of the capacity N of the positive electrode plate per unit area to the capacity P of the negative electrode plate per unit area is 0.3.
Example 9
The method for preparing the positive electrode comprises the following steps: the weight of the first positive electrode slurry applied on both sides when forming the first positive electrode active material layer was 61g/m2The thickness of the porous metal aluminum foil used was 8 μm, and the double-side coating weight of the first positive electrode slurry when the second positive electrode active material layer was formed was 61g/m2Otherwise, the second positive active material layer in the positive electrode sheet was obtained in the same manner as in example 1, and accounted for 50% of the total mass of the positive electrode sheet.
The method for preparing the negative electrode plate is the same as that in example 1, wherein the ratio of the capacity N of the positive electrode plate per unit area to the capacity P of the negative electrode plate per unit area is 0.5.
Example 10
The method for preparing the positive electrode comprises the following steps: the weight of the first positive electrode slurry applied on both sides when forming the first positive electrode active material layer was 61g/m2The thickness of the porous metal aluminum foil used was 10 μm, and the double-side coating weight of the first positive electrode slurry when the second positive electrode active material layer was formed was 61g/m2Otherwise, the second positive active material layer in the positive electrode sheet was obtained in the same manner as in example 1, and accounted for 50% of the total mass of the positive electrode sheet.
The method for preparing the negative electrode plate is the same as that in example 1, wherein the ratio of the capacity N of the positive electrode plate per unit area to the capacity P of the negative electrode plate per unit area is 0.5.
Example 11
The method for preparing the positive electrode comprises the following steps: the weight of the first positive electrode slurry applied on both sides when forming the first positive electrode active material layer was 61g/m2The thickness of the porous metal aluminum foil is adopted8 μm, the size of the pores in the porous metal layer is 3mm, the gap between adjacent pores is 1mm, and the weight of the first positive electrode slurry coated on both sides when the second positive electrode active material layer is formed is 61g/m2Otherwise, the second positive active material layer in the positive electrode sheet was obtained in the same manner as in example 1, and accounted for 50% of the total mass of the positive electrode sheet.
The method for preparing the negative electrode plate is the same as that in example 1, wherein the ratio of the capacity N of the positive electrode plate per unit area to the capacity P of the negative electrode plate per unit area is 0.5.
Example 12
The method for preparing the positive electrode comprises the following steps: the weight of the first positive electrode slurry applied on both sides when forming the first positive electrode active material layer was 61g/m2The thickness of the porous metal aluminum foil is 8 μm, the size of the holes in the porous metal layer is 5mm, the gap between adjacent holes is 1mm, and the double-sided coating weight of the first positive electrode slurry is 61g/m when the second positive electrode active material layer is formed2Otherwise, the second positive active material layer in the positive electrode sheet was obtained in the same manner as in example 1, and accounted for 50% of the total mass of the positive electrode sheet.
The method for preparing the negative electrode plate is the same as that in example 1, wherein the ratio of the capacity N of the positive electrode plate per unit area to the capacity P of the negative electrode plate per unit area is 0.5.
Example 13
The method for preparing the positive electrode comprises the following steps: the weight of the first positive electrode slurry applied on both sides when forming the first positive electrode active material layer was 61g/m2The thickness of the porous metal aluminum foil is 8 μm, the size of the holes in the porous metal layer is 1mm, the gap between adjacent holes is 3mm, and the double-sided coating weight of the first positive electrode slurry is 61g/m when the second positive electrode active material layer is formed2Otherwise, the second positive active material layer in the positive electrode sheet was obtained in the same manner as in example 1, and accounted for 50% of the total mass of the positive electrode sheet.
The method for preparing the negative electrode plate is the same as that in example 1, wherein the ratio of the capacity N of the positive electrode plate per unit area to the capacity P of the negative electrode plate per unit area is 0.5.
Example 14
The method for preparing the positive electrode comprises the following steps: the weight of the first positive electrode slurry applied on both sides when forming the first positive electrode active material layer was 61g/m2Porous metallic aluminium usedThe foil thickness was 8 μm, the pore size in the porous metal layer was 1mm, the gap between adjacent pores was 5mm, and the double-sided coating weight of the first positive electrode slurry when the second positive electrode active material layer was formed was 61g/m2Otherwise, the second positive active material layer in the positive electrode sheet was obtained in the same manner as in example 1, and accounted for 50% of the total mass of the positive electrode sheet.
The method for preparing the negative electrode plate is the same as that in example 1, wherein the ratio of the capacity N of the positive electrode plate per unit area to the capacity P of the negative electrode plate per unit area is 0.5.
Example 15
The method for preparing the positive electrode comprises the following steps: the double-sided coating weight of the first positive electrode slurry in forming the first positive electrode active material layer was 85.4g/m2The thickness of the porous metal aluminum foil used was 8 μm, and the double-side coating weight of the first positive electrode slurry when the second positive electrode active material layer was formed was 36.6g/m2Otherwise, the second positive electrode active material layer in the positive electrode sheet was obtained in the same manner as in example 1, and accounted for 30% of the total mass of the positive electrode sheet.
The method for preparing the negative electrode plate is the same as that in example 1, wherein the ratio of the capacity N of the positive electrode plate per unit area to the capacity P of the negative electrode plate per unit area is 0.5.
Example 16
The method for preparing the positive electrode comprises the following steps: the double-sided coating weight of the first positive electrode slurry in forming the first positive electrode active material layer was 36.6g/m2The thickness of the porous metal aluminum foil used was 8 μm, and the double-side coating weight of the first positive electrode slurry when the second positive electrode active material layer was formed was 85.4g/m2Otherwise, the second positive active material layer in the positive electrode sheet was obtained in the same manner as in example 1, and accounted for 70% of the total mass of the positive electrode sheet.
The method for preparing the negative electrode plate is the same as that in example 1, wherein the ratio of the capacity N of the positive electrode plate per unit area to the capacity P of the negative electrode plate per unit area is 0.5.
Example 17
The method for preparing the positive electrode comprises the following steps: the weight of the first positive electrode slurry applied on both sides when forming the first positive electrode active material layer was 61g/m2When a triangular porous metal aluminum foil with a thickness of 8 μm is used to form the second positive electrode active material layerThe double-sided coating weight of the first positive electrode slurry was 61g/m2Otherwise, the second positive active material layer in the positive electrode sheet was obtained in the same manner as in example 1, and accounted for 50% of the total mass of the positive electrode sheet.
The method for preparing the negative electrode plate is the same as that in example 1, wherein the ratio of the capacity N of the positive electrode plate per unit area to the capacity P of the negative electrode plate per unit area is 0.5.
Example 18
The method for preparing the positive electrode comprises the following steps: the weight of the first positive electrode slurry applied on both sides when forming the first positive electrode active material layer was 61g/m2A quadrangular porous metal aluminum foil having a thickness of 8 μm was used, and the weight of the first positive electrode slurry applied on both sides when the second positive electrode active material layer was formed was 61g/m2Otherwise, the second positive active material layer in the positive electrode sheet was obtained in the same manner as in example 1, and accounted for 50% of the total mass of the positive electrode sheet.
The method for preparing the negative electrode plate is the same as that in example 1, wherein the ratio of the capacity N of the positive electrode plate per unit area to the capacity P of the negative electrode plate per unit area is 0.5.
Example 19
The method for preparing the positive electrode comprises the following steps: the weight of the first positive electrode slurry applied on both sides when forming the first positive electrode active material layer was 61g/m2The first positive electrode slurry is formed by mixing a quadrangular porous metal aluminum foil and a circular porous metal aluminum foil to form a porous metal layer, the thickness of the porous metal aluminum foil is 8 mu m, and the double-side coating weight of the first positive electrode slurry is 61g/m when a second positive electrode active material layer is formed2Otherwise, the second positive active material layer in the positive electrode sheet was obtained in the same manner as in example 1, and accounted for 50% of the total mass of the positive electrode sheet.
The method for preparing the negative electrode plate is the same as that in example 1, wherein the ratio of the capacity N of the positive electrode plate per unit area to the capacity P of the negative electrode plate per unit area is 0.5.
Comparative example
The method for preparing the positive electrode comprises the following steps:
(1) homogenizing graphite particles, SBR (styrene butadiene rubber), CMC (sodium carboxymethylcellulose) and SP (conductive carbon black) according to a weight ratio of 95:2.5:1.5:1, wherein water is added to control the solid content to be 45-55% and the viscosity to be 2000-4000 mpa · s, and stirring is finished to obtain anode slurry;
(2) uniformly coating the first positive electrode slurry on the surface of a copper foil base material with the thickness of 8 mu m, wherein the coating weight of the first positive electrode slurry on two sides is 270g/m2And then drying, rolling, die cutting and punching to obtain the positive pole piece.
The method for preparing the negative electrode plate is the same as that in example 1, wherein the ratio of the capacity N of the positive electrode plate per unit area to the capacity P of the negative electrode plate per unit area is 1.1.
The diaphragm adopts a polyethylene PE diaphragm with the thickness of 16 mu m, and the electrolyte comprises lithium salt LiPF6And a solvent, wherein the solvent includes Ethylene Carbonate (EC), diethyl carbonate (DEC), and methylethyl carbonate (EMC), lithium salt LiPF6The concentration of (A) is 1.2mol/L, and the molar ratio of DEC, EC and EMC is 1: 1: 1, taking the positive pole piece and the negative pole piece corresponding to the examples 1-19 and the comparative examples, stacking the positive pole, the diaphragm, the negative pole, the diaphragm and the positive pole layer by layer in sequence, manufacturing a naked battery cell, controlling the thickness of each naked battery cell to be consistent by controlling the number of the stacked positive and negative poles, then putting the naked battery cells into a shell, baking, injecting liquid, forming, and sealing to manufacture the battery cell.
The cell capacities, internal resistances and energy densities obtained in examples 1 to 18 and comparative example were evaluated:
1. the capacity testing method comprises the following steps: at room temperature, taking three cells in each of the comparative example and examples 1-19, charging the cells to 4.2V at constant current and constant voltage according to the charging 0.33C by adopting a charging and discharging test cabinet, standing for 10min, discharging the cells to 2.8V according to the discharging 0.33C, and recording the discharging capacity;
2. the internal resistance testing method comprises the following steps: testing the impedance of the battery cores of comparative examples 1-4 and examples 1-4 by using a resistance tester and recording the value;
3. the weight test method comprises the following steps: the cell weights of comparative examples 1 to 4 and examples 1 to 4 were measured by an electronic scale, and the cell energy density was calculated according to the formula cell energy density ═ discharge capacity-discharge plateau voltage/cell weight.
The results of the cell capacity, internal resistance and energy density tests obtained in examples 1 to 19 and comparative example are shown in table 1.
TABLE 1
Figure RE-GDA0002965790090000141
Figure RE-GDA0002965790090000151
Figure RE-GDA0002965790090000161
And (4) conclusion: from the cell capacity, internal resistance and energy density data of comparative example 1 and examples 1-19, it can be seen that the cell capacity and energy density are increased in examples 1-5, but the increase of examples 1-4 is smaller, and the increase of example 5 is larger, compared to the comparative example, because the low N/P reduces the coating weight of the positive electrode slurry, more active material can be filled in the same space, and the effective energy exertion can be improved, but the porous metal aluminum foil does not belong to the active material, does not participate in the capacity exertion, and the existence of the porous metal aluminum foil will cause the capacity exertion to be reduced, so the optimal porous metal aluminum foil thickness exists for a certain N/P value, such as example 5 and example 9. The influence of different porous metal aluminum foil thicknesses on the capacity depends on the N/P ratio, and a certain N/P ratio corresponds to the optimal porous metal aluminum foil thickness with the maximum capacity, because the thickness is relatively small, active lithium caused by excessive negative electrode capacity cannot completely react with the porous metal aluminum foil to generate a lithium metal alloy, so that part of lithium still deposits on the surface of the positive electrode in a dendrite form, and possibly causes that part of lithium becomes dead lithium which cannot participate in charging and discharging any more, the charging cannot be fully charged, and the discharging cannot be completely discharged, so that the discharging capacity is reduced, as in example 8; if the thickness of the porous metal foil is too large, a part of the porous metal foil cannot function, but occupies the effective space of the battery cell, thereby deteriorating the energy density of the battery cell, as in example 10. In addition, the porous metal aluminum foil layer has no deterioration phenomenon on the internal resistance.
The cell dc impedances and powers obtained in examples 1 to 19 and comparative example were evaluated:
the test method comprises the following steps: at room temperature, 2 of each of the battery cells of examples 1 to 19 and comparative example were charged to 4.2V with a 0.33C constant current and voltage, then discharged for 30min to 50% SOC with 1C, discharged for 10S with 4C current, and voltage values before and after discharge were recorded, and dc impedance and power were calculated as dc impedance (voltage before discharge-voltage after discharge)/discharge current, and power ((voltage before discharge-lower limit voltage) · lower limit voltage)/dc impedance.
The cell dc impedance and power test data obtained for examples 1-19 and comparative examples are shown in table 2.
TABLE 2
Figure RE-GDA0002965790090000171
Figure RE-GDA0002965790090000181
And (4) conclusion: from the cell dc impedance and power data of comparative example and examples 1 to 19, it can be seen that the dc impedance and power in the examples are not deteriorated and are slightly better than the comparative example, and as the N/P ratio is decreased, there is an advantage of a reinforced phenomenon because the low N/P ratio results in a slightly lower coating weight of the positive paste, the number of lamination layers is increased, which is equivalent to an increase in the number of parallel connections in the cell, and thus the impedance can be decreased. The influence of different porous metal aluminum foil thicknesses on impedance and power depends on the N/P ratio, and a certain N/P ratio corresponds to the optimal porous metal aluminum foil thickness with the maximum power, because on one hand, the coating weight of the positive electrode slurry is reduced, so that the coating thickness of the active material is reduced, the impedance can be reduced, and the power is improved, but on the other hand, the porous metal aluminum foil is positioned in the active material layer, so that the migration of lithium ions in the active material layer can be deteriorated, the power can be deteriorated, and in addition, the condition that the surface coating is insufficient under the low N/P ratio can lead to the generation of lithium ions, which can block the migration of the lithium ions, and can also lead to the reduction of. In addition, the size, the space and the shape of the holes of the porous metal aluminum foil have no influence on the power performance, and the content of the active substance layer on the upper layer of the porous metal foil has no influence on the power.
The cycle life, swelling capacity, gassing behavior and storage life of the cells obtained in examples 1 to 19 and comparative example were evaluated:
1. the cycle life testing method comprises the following steps: at room temperature, 2 cells of each of the comparative example and the examples 1 to 19 were charged to 4.2V with a constant current and a constant voltage of 0.33C, left for 5min, and then discharged to 2.8V with 0.33C, and the discharge capacity was recorded, the capacity retention rate being the corresponding cycle discharge capacity/initial discharge capacity, and the process was repeated until the capacity retention rate was not more than 80%, and the number of cycles was recorded.
2. And testing the gas production rate and the expansion force change condition in the circulation process by using a gas production tester and an expansion force testing device.
3. The storage life testing method comprises the following steps: at room temperature, 2 cells of each of the comparative examples and examples 1 to 19 were charged to 4.2V with a constant current and a constant voltage of 0.33C, and then the cells were placed in a high-temperature 45 ℃ incubator, stored for 500 days, and taken out every 30 days to test the capacity retention rate.
The cell cycle life, swell force, gassing and storage life test data obtained for examples 1-19 and comparative example are shown in table 3.
TABLE 3
Figure RE-GDA0002965790090000191
Figure RE-GDA0002965790090000201
And (4) conclusion: from the cell cycle life, swelling power, gas generation condition and storage life data of the comparative example and examples 1 to 19, it can be seen that cycle life, gas generation, swelling and storage life of the examples are not deteriorated and are slightly superior to those of the comparative example, and as the N/P ratio is decreased, there is an advantage of a strengthening phenomenon in that the potential of the negative electrode becomes lower at 100% SOC due to the low N/P ratio, which weakens the oxidation effect on the electrolyte. The influence of different porous metal aluminum foil thicknesses on the cycle life and the storage life depends on the N/P ratio, and a certain N/P ratio corresponds to the porous metal aluminum foil thickness threshold with optimal cycle and storage performances, because the lithium metal alloy can be completely reacted with active lithium under a certain N/P ratio in the whole life cycle, the thickness of the lithium metal alloy is lower than the thickness, dead lithium can be caused along with the cycle, the dead lithium is gradually increased along with the charge and discharge, the capacity is rapidly reduced, the gas generation and expansion are increased and deteriorated, like example 8, the thickness is higher than the thickness, and the cycle and storage performances have no obvious difference. In addition, the size, the space and the shape of the holes of the porous metal aluminum foil have no influence on the circulation and storage performance, and the content of the active substance layer on the upper layer of the porous metal aluminum foil has no influence on the circulation and storage performance.
The safety performance of the cells of examples 1 to 19 and comparative examples was evaluated:
at room temperature, 4 cells of comparative example and EOL (after cycle test) of examples 1 to 19 were charged to 4.2V with a constant current and a constant voltage of 0.33C, 2 cells were then tested in a hot box and extrusion, the initial temperature of the hot box was 25 ℃, the heating rate was 5 ℃/min, the temperature was raised to 130 ℃ and then kept for 30min, and the cell condition was observed. And (3) testing the extrusion speed by extrusion at 2mm/s, stopping extrusion when the voltage reaches 0V or the deformation reaches 15% or the extrusion force reaches 100KN, standing for 1h, and observing the state of the battery cell.
Examples 1-19 and comparative cell safety performance data are shown in table 4.
TABLE 4
Figure RE-GDA0002965790090000211
Figure RE-GDA0002965790090000221
And (4) conclusion: through the test data of the safety performance of the battery cells in the comparative example and the examples 1 to 19, it can be seen that the safety performance of the battery cells manufactured by the preferred schemes (except the example 8) introduced by the patent of the invention has no difference, and the battery cells meet the requirements of the current power batteries.
In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.
Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.

Claims (10)

1. A positive electrode, comprising:
a positive current collector;
a first positive electrode active material layer formed on the surface of the positive electrode current collector;
a porous metal layer formed on a surface of the first positive electrode active material layer;
a second positive electrode active material layer formed on a surface of the porous metal layer.
2. The positive electrode according to claim 1, wherein the pore shape of the porous metal layer is a circle or a polygon;
optionally, the size of the holes is 0.1-10 mm;
optionally, the gap between two adjacent holes is 0.5-30 mm.
3. The positive electrode according to claim 1, wherein the positive electrode is a lithium secondary batteryThe first positive electrode active material layer and the second positive electrode active material layer each independently include a graphite material and Si-SiO2At least one of the alloy materials.
4. The positive electrode according to claim 1, comprising a plurality of porous metal layers, wherein the first positive electrode active material layer or the second positive electrode active material layer is disposed between adjacent porous metal layers, and the first positive electrode active material layer or the second positive electrode active material layer is disposed on the most distal end of the positive electrode current collector.
5. The positive electrode according to claim 4, wherein the first positive electrode active material layer or the second positive electrode active material layer corresponding to the farthest end on the positive electrode current collector accounts for 5 to 95% of the total mass of the positive electrode.
6. The positive electrode according to claim 4, wherein the thickness of the single porous metal layer is 2 to 20 μm;
optionally, the porous metal layer comprises at least one of metallic aluminum, metallic tin, an aluminum tin alloy, an aluminum copper alloy, and an aluminum copper iron alloy.
7. A method of preparing the positive electrode of any one of claims 1 to 6, comprising:
(1) mixing a first positive electrode active material, a binder, a conductive agent, and a thickener to obtain a first positive electrode slurry;
(2) applying the first positive electrode slurry on a positive electrode current collector surface to form a first positive electrode active material layer on the positive electrode current collector surface;
(3) applying a porous metal on the first positive electrode active material layer to form a porous metal layer on a surface of the first positive electrode active material layer;
(4) mixing a second positive electrode active material, a binder, a conductive agent, and a thickener to obtain a second positive electrode slurry;
(5) the second positive electrode slurry is applied on the surface of the porous metal layer to obtain a positive electrode.
8. A lithium ion battery, comprising a positive electrode, a negative electrode, an electrolyte and a separator, wherein the positive electrode is the positive electrode according to any one of claims 1 to 6 or the positive electrode obtained by the method according to claim 7,
wherein the ratio of the unit area capacity of the positive electrode to the unit area capacity of the negative electrode is not higher than 1, preferably 0.4-0.7.
9. The lithium ion battery of claim 8, wherein the negative electrode comprises a metal oxide material having the formula LiNixCoyMnzFeaAlbPcO2Wherein x is more than or equal to 0 and less than or equal to 1, y is more than or equal to 0 and less than or equal to 1, z is more than or equal to 0 and less than or equal to 1, a is more than or equal to 0 and less than or equal to 1, b is more than or equal to 0 and less than or equal to 0.8, and c is more than or equal to 0.
10. A vehicle characterized in that it comprises the lithium ion battery of claim 8 or 9.
CN202011598489.9A 2020-12-29 2020-12-29 Positive electrode and preparation method and application thereof Pending CN112652754A (en)

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CN111785923A (en) * 2020-07-31 2020-10-16 蜂巢能源科技有限公司 Lithium ion battery anode, preparation method and application thereof, and lithium ion battery

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Application publication date: 20210413