CN112216878B

CN112216878B - Lithium ion battery repeating unit, lithium ion battery, using method of lithium ion battery, battery module and automobile

Info

Publication number: CN112216878B
Application number: CN201910621846.XA
Authority: CN
Inventors: 李世彩; 王蒙; 焦晓朋; 李向辉; 甘永青
Original assignee: BYD Co Ltd
Current assignee: BYD Co Ltd
Priority date: 2019-07-10
Filing date: 2019-07-10
Publication date: 2021-11-12
Anticipated expiration: 2039-07-10
Also published as: CN112216878A

Abstract

The present disclosure relates to a lithium ion battery repeating unit, a lithium ion battery and a method of using the same, a battery module and an automobile, the repeating unit includes an anode, a first separator and a cathode that are sequentially stacked in a stacking direction, the cathode includes a first cathode and a second cathode that are in electrical contact with each other when charged; the first negative electrode includes an active material layer, a conductor layer, and an insulating layer; in the negative electrode, an active material layer, a conductor layer, an insulating layer, a second negative electrode, an insulating layer, a conductor layer, and an active material layer are sequentially stacked in a stacking direction. The lithium ion battery disclosed by the invention has higher energy density and can overcome the safety problem caused by lithium dendrite in the existing battery.

Description

Lithium ion battery repeating unit, lithium ion battery, using method of lithium ion battery, battery module and automobile

Technical Field

The disclosure relates to the field of batteries, in particular to a lithium ion battery repeating unit, a lithium ion battery, a using method of the lithium ion battery repeating unit, a battery module and an automobile.

Background

There are generally two types of batteries currently used in the market: an energy conversion device which separates an energy storage active material from an electric stack which provides a chemical reaction site, represented by a fuel flow battery or a flow battery; and the other is formed by uniformly laminating or winding the anode, the diaphragm and the cathode, and the active substance is distributed on the anode and the cathode to form an energy conversion device which stores energy and integrates power. The lithium ion battery belongs to a typical second type, and the positive electrode, the diaphragm and the negative electrode of the lithium ion battery are uniformly arranged in opposite directions. The anode comprises an anode current collector and an anode material, wherein the anode material can be divided into an anode active substance material, an anode electronic conductive additive material and an anode ion conductive material; the membrane comprises two parts, namely an electron blocking part and an ion conducting part; the negative electrode is similar to the positive electrode and comprises a negative electrode current collector and a negative electrode material, wherein the negative electrode material can be divided into a negative electrode active material, a negative electrode electronic conductive additive material and a negative electrode ionic conductive material.

The chemical compositions and structures of the cathode material and the anode material of the traditional lithium ion battery are almost uniform, and a small amount of mixed materials are also used, but even if the mixed materials are used, the concentrations of ions and electrons in the same time and the same region in the battery are basically consistent, so that the purpose is to ensure the stability of parameters such as electrochemical reaction, power and the like.

In order to increase the energy density, it is necessary to increase the voltage and capacity of the positive electrode active material in the battery as much as possible, and the negative electrode active material needs to decrease the voltage and increase the capacity as much as possible. Conventional commercial negative active material materials are generally graphite including natural graphite and artificial graphite, both of which have an average voltage (vs. li) of 0.15V. The theoretical capacities were all 372 mAh/g. Therefore, a great deal of scientific research is being conducted worldwide in order to find negative active material materials of lower voltage and higher capacity. Lithium metal is one of the most potential materials, and the voltage is the lowest of all the chemical substances at present; the theoretical capacity of the graphite anode material reaches 3860mAh/g, which is 10 times of that of the graphite anode material.

However, lithium metal cannot be used in a delayed manner, and the greatest problem is that it forms a large number of dendrites during cycling until the entire lithium metal planar layer is completely converted into a dendrite form. This dendrite morphology creates two serious problems: firstly, the puncture penetrates through the diaphragm to connect the positive electrode and the negative electrode, so that short circuit is caused, and serious safety accidents are caused; and secondly, because the dendritic crystal has large surface area, the dendritic crystal and electrolyte generate in-situ chemical reaction when being generated, an electronic insulation film is formed on the surface of the dendritic crystal, the film causes mutual electronic insulation among the crystals, once a root system is broken, the whole dendritic crystal becomes an electronic insulator, the electrochemical activity is lost, and the battery capacity is continuously and rapidly reduced along with circulation. Thirdly, the dendritic crystal is extremely fluffy and needs to occupy a large amount of space, so that the volume of the battery is expanded, and the cycle performance of the battery is rapidly attenuated.

Disclosure of Invention

The purpose of the present disclosure is to provide a lithium ion battery repeating unit, a lithium ion battery, a method for using the same, a battery module and an automobile, so as to solve the problem of low energy density of the battery and the safety problem caused by lithium dendrite in the prior art.

In order to achieve the above object, a first aspect of the present disclosure provides a lithium ion battery repeating unit: the repeating unit includes a positive electrode, a first separator, and a negative electrode that are sequentially stacked in a stacking direction, the negative electrode including a first negative electrode and a second negative electrode that are in electrical contact with each other when charged; the first negative electrode includes an active material layer, a conductor layer, and an insulating layer; in the negative electrode, the active material layer, the conductor layer, the insulating layer, the second negative electrode, the insulating layer, the conductor layer, and the active material layer are sequentially stacked in the stacking direction.

Optionally, the conductor layer comprises an inorganic porous conductive material and the insulating layer comprises a first organic porous separator material.

Optionally, the inorganic porous conductive material is one or more of a porous metal material, a porous carbon material and a porous oxide material.

Optionally, the porous metal material is a metal mesh or a metal foam; the metal in the porous metal material is one or more of copper, nickel, magnesium, aluminum, manganese, iron, titanium and zinc;

the porous carbon material is porous carbon spheres, porous carbon fibers, porous carbon nanotubes or porous carbon cloth, or a combination of two or three of the porous carbon spheres, the porous carbon fibers, the porous carbon nanotubes or the porous carbon cloth;

the porous oxide material is a metal oxide or the metal oxide modified by doping; the metal oxide is at least one selected from indium oxide, tin oxide, indium tin oxide, ruthenium dioxide, zinc oxide and silver oxide, and the doping element in the doped and modified metal oxide is at least one selected from carbon, boron, phosphorus, nitrogen, sulfur, selenium, chlorine, iodine and fluorine.

Optionally, the first organic porous membrane material is one of a porous PE membrane, a porous PP membrane, a porous PET membrane, a porous PAN membrane, a porous PI membrane, and a porous PVDF membrane, or a porous composite membrane formed by several of them.

Optionally, the pores of the inorganic porous conductive material and/or the first organic porous separator material are filled with an electrolyte, and the electrolyte is a liquid electrolyte.

Optionally, the liquid electrolyte is one or more of an ester solution of lithium salt, an ether solution and a sulfone solution;

the lithium salt comprises LiPF₆、LiClO₄、LiBF₄、LiAsF₆、LiSiF₆、LiB(C₆H₅)₄、LiCl、LiBr、LiAlCl₄、LiC(SO₂CF₃)₃、LiCH₃SO₃、LiN(SO₂CF₃)₂And LiN (SO)₂C₂F₅)₂One or more of them.

Optionally, the surface of the conductor layer, which is in contact with the active material layer, is coated with a carbon coating, the carbon material of the carbon coating is one or more of graphite, hard carbon, soft carbon, mesocarbon microbeads, carbon nanotubes, graphene and carbon fibers, and the thickness of the carbon coating is 0.1-10 μm.

Optionally, the second negative electrode is one or more of a non-conductive body formed with a conductive protrusion, a solid metal body and a metal body having a porous structure; the metal body having a porous structure includes at least one of a metal mesh, a metal foam, and a metal body having surface pores.

Optionally, the second negative electrode is coated with a lithium coating, and the amount of the lithium coating is 0.026-2.6 mg/cm based on the unit surface area of the second negative electrode²。

Optionally, the metal body having the surface pores includes a first porous portion, a solid metal portion, and a second porous portion provided in this order in the stacking direction, the first porous portion and the second porous portion each having a through hole extending in the stacking direction.

Optionally, the apertures of the through holes of the first porous portion are flared in the stacking direction, and/or the apertures of the through holes of the second porous portion are tapered in the stacking direction;

preferably, the through hole is filled with lithium.

Optionally, a second organic porous separator material layer is included between the second negative electrode and the insulating layer, and the second organic porous separator material layer is a layer formed by one or more of a porous PE separator, a porous PP separator, a porous PET separator, a porous PAN separator, a porous PI separator, and a porous PVDF separator.

Optionally, the material of the active material layer is one or more of natural graphite, artificial graphite, hard carbon, soft carbon, lithium titanate, iron oxide, lithium titanium phosphate, titanium dioxide, silicon oxide, aluminum, tin and antimony.

In a second aspect of the present disclosure: a lithium ion battery is provided that includes one or more lithium ion battery repeat units provided by the first aspect of the present disclosure.

Optionally, a second membrane is disposed between adjacent repeating units.

A third aspect of the disclosure: there is provided a method of using a lithium ion battery provided in a second aspect of the present disclosure, the method comprising the steps of: when charging, the second negative electrode is charged until the battery capacity reaches Y, and then the first negative electrode is charged until the battery capacity reaches Y + X.

A fourth aspect of the present disclosure: there is provided a battery module including the lithium ion battery provided in the third aspect of the present disclosure.

The fifth aspect of the present disclosure: an automobile is provided, which comprises the battery module provided by the fourth aspect of the disclosure.

Through above-mentioned technical scheme, this disclosure can realize following beneficial effect:

first, through setting up first negative pole and second negative pole for metal lithium can carry out the accumulate in first negative pole and second negative pole department, makes the energy of whole negative pole system obtain promoting by a wide margin, and then makes lithium ion battery's energy density compare traditional structure battery and promote by a wide margin.

Secondly, because the capacity set values of the first negative electrode and the second negative electrode are controlled, the metal lithium generated during charging is only filled and concentrated between the insulating layer and the second negative electrode, the penetration of lithium dendrites cannot occur, and the short circuit risk in the traditional battery structure is overcome.

And thirdly, during discharging, the first negative electrode and the second negative electrode can be in parallel discharging, so that the defect of poor rate capability of the traditional lithium metal negative electrode battery is overcome.

Additional features and advantages of the disclosure will be set forth in the detailed description which follows.

Drawings

The accompanying drawings, which are included to provide a further understanding of the disclosure and are incorporated in and constitute a part of this specification, illustrate embodiments of the disclosure and together with the description serve to explain the disclosure without limiting the disclosure. In the drawings:

fig. 1 is a schematic structural diagram of one specific embodiment of a lithium ion battery provided by the present disclosure.

Fig. 2 is a schematic structural diagram of a conventional lithium ion battery.

Fig. 3 is a schematic structural diagram of a specific embodiment of a second negative electrode in a repeating unit of a lithium ion battery provided by the present disclosure.

Fig. 4 is a schematic structural diagram of another embodiment of a second negative electrode in a repeating unit of a lithium ion battery provided by the present disclosure.

Fig. 5 is a schematic structural diagram of another embodiment of a second negative electrode in a repeating unit of a lithium ion battery provided by the present disclosure.

Fig. 6 is an SEM micrograph of lithium metal cycling as a negative electrode to form dendrites in the cell of comparative example 3.

Fig. 7 is a discharge voltage curve of the positive electrode and the negative electrode of the battery of comparative example 2 against the reference electrode, respectively.

Fig. 8 is a voltage graph of the positive electrode and the first negative electrode of the battery of example 3 with respect to the second negative electrode.

Fig. 9 is a voltage graph of the positive electrode and the second negative electrode of the battery of example 3 with respect to the first negative electrode.

Description of the reference numerals

1 first negative electrode 11 active material layer

12 conductor layer 13 insulating layer

2 second negative electrode 21 first porous part

22 solid metal portion 23 second porous portion

3 positive electrode 31 positive electrode current collector

32 positive electrode material 4 separator

5 negative electrode 51 negative electrode material

52 negative electrode current collector 6 lithium

Detailed Description

The following detailed description of specific embodiments of the present disclosure is provided in connection with the accompanying drawings. It should be understood that the detailed description and specific examples, while indicating the present disclosure, are given by way of illustration and explanation only, not limitation.

The first aspect of the disclosure: providing a lithium ion battery repeating unit, referring to fig. 1, the repeating unit includes a positive electrode 3, a first separator 4, and a negative electrode, which are sequentially stacked in a stacking direction, the negative electrode including a first negative electrode 1 and a second negative electrode 2 that are not in electrical contact with each other when charged; the first negative electrode 1 includes an active material layer 11, a conductor layer 12, and an insulating layer 13; in the negative electrode, an active material layer 11, a conductor layer 12, an insulating layer 13, a second negative electrode 2, an insulating layer 13, a conductor layer 12, and an active material layer 11 are sequentially stacked in the stacking direction.

According to the present disclosure, the anode 5 may include an anode material 51 and an anode current collector 52. In contrast to the prior art lithium ion battery (fig. 2), the lithium ion battery repeating unit of the present disclosure is a dual negative electrode structure, wherein the first negative electrode 1 may include an active material layer 11, a conductor layer 12, and an insulating layer 13, and the presence of the insulating layer 13 allows the first negative electrode 1 and the second negative electrode 2 to be in electrical contact with each other when charged. Through setting up first negative pole and second negative pole for metal lithium can carry out the accumulate in first negative pole and second negative pole department, makes the energy of whole negative pole system promote by a wide margin, and then makes the energy density of the lithium ion battery who has this disclosed repetitive unit compare traditional structure battery and promote by a wide margin. The positive electrode 3 may include a positive electrode collector 31, and a surface of the positive electrode collector 31 may be coated with a positive electrode material 32, for example, a surface adjacent to the first separator 4 may be coated with the positive electrode material 32. Here, the stacking direction refers to a direction in which the functional layers from the cathode to the anode are stacked in the repeating unit, and is, for example, a direction from left to right in fig. 1 horizontally.

According to the present disclosure, the conductor layer 12 may be a layer containing a conductive material, the insulating layer 13 may be a layer containing an insulating material, and the conductor layer 12 and the insulating layer 13 stacked may be such that the first negative electrode is not conductive in the stacking direction and is conductive in a direction perpendicular to the stacking direction. Preferably, the conductor layer 12 may contain an inorganic porous conductive material, and the insulating layer 13 may contain a first organic porous separator material. According to the present disclosure, the inorganic porous conductive material and the first organic porous separator material may have a porous structure, respectively, wherein parameters such as the shape, number, pore size, and the like of pores may be conventional in the art, and the present disclosure is not particularly limited. The porous structures of the inorganic porous conductive material and the first organic porous diaphragm material can keep the smoothness of a lithium ion passage in the battery, and normal charge-discharge reaction of the battery is realized. The organic porous diaphragm material is used as an electronic insulating material, and has the advantages of good compatibility with electrolyte, mature technology, low manufacturing cost and easy obtainment.

In one embodiment, the repeating unit may further include a positive electrode tab, a first negative electrode tab, and a second negative electrode tab; the two first cathodes 1 of the repeating unit may be respectively connected with a first cathode tab, the second cathode 1 may be connected with a second cathode tab, and the anode 3 may be connected with an anode tab.

According to the present disclosure, the inorganic porous conductive material may be one or more of a porous metal material, a porous carbon material, and a porous oxide material.

Further, the porous metal material may be a metal mesh or a foamed metal, and the metal element in the porous metal material may be one or more selected from copper, nickel, magnesium, aluminum, manganese, iron, titanium and zinc, that is, the porous metal material may be, for example, a copper mesh, a foamed copper, a nickel mesh, a foamed nickel, and the like. When the inorganic porous conductive material is a porous metal material, the inorganic porous conductive material has the advantages of high mechanical strength and good conductivity, and can further improve the conductivity and the mechanical strength of the lithium ion battery repeating unit.

Further, the porous carbon material may be porous carbon spheres, porous carbon fibers, porous carbon nanotubes or porous carbon cloth, or a combination of two or three of them. When the inorganic porous conductive material is a porous carbon material, the advantages are light weight and high energy density.

Further, the porous oxide material is a metal oxide or a doped modified metal oxide; the metal oxide is at least one selected from indium oxide, tin oxide, indium tin oxide, ruthenium dioxide, zinc oxide and silver oxide, and the doping element in the doping modified metal oxide can be at least one selected from carbon, boron, phosphorus, nitrogen, sulfur, selenium, chlorine, iodine and fluorine. When the inorganic porous conductive material is porous oxide, the lithium ion battery repeating unit disclosed by the invention has good thermal stability and safety.

According to the present disclosure, the first organic porous separator material may be various separator materials used in a lithium ion battery well known to those skilled in the art, and may be, for example, one of a porous PE (polyethylene) separator, a porous PP (polypropylene) separator, a porous PET (polyethylene terephthalate) separator, a porous PAN (polyacrylonitrile) separator, a porous PI (polyimide) separator, and a porous PVDF (polyvinylidene fluoride) separator, or a porous composite separator formed of several of them. The first organic porous diaphragm material is used as an electronic insulating material in the lithium ion battery repeating unit, is widely used in the conventional lithium ion battery system, can be conveniently introduced into the battery system, and has the advantages of good compatibility with an electrolyte, mature technology, low manufacturing cost and easiness in obtaining.

In a preferred embodiment, the pores of the inorganic porous conductive material and/or the first organic porous separator material are filled with a liquid electrolyte. Thus, a lithium ion path inside the battery can be secured.

Further, the liquid electrolyte may be an ester solution, an ether solution, or a sulfone solution of a lithium salt, which may include lithium hexafluorophosphate (LiPF), or a combination of two or three thereof₆) Lithium perchlorate (LiClO)₄) Lithium tetrafluoroborate (LiBF)₄) Lithium hexafluoroarsenate (LiAsF)₆) Lithium hexafluorosilicate (LiSiF)₆) Lithium tetraphenylborate (LiB (C)₆H₅)₄) Lithium chloride (LiCl), lithium bromide (LiBr), lithium chloroaluminate (LiAlCl)₄) Fluorine fluorosulfonic acid lithium (LiC (SO)₂CF₃)₃)、LiCH₃SO₃、LiN(SO₂CF₃)₂、LiN(SO₂C₂F₅)₂One or more of them.

According to the present disclosure, the first negative electrode 1 may be coated with a carbon coating layer, preferably, a carbon coating layer is coated on a surface of the conductor layer 12 contacting the active material layer 11. The carbon material of the carbon coating may be one or more conventionally used by those skilled in the art, such as graphite, hard carbon, soft carbon, mesocarbon microbeads, carbon nanotubes, graphene and carbon fibers. The thickness of the carbon coating can be changed in a large range, and preferably, the thickness of the carbon coating can be 0.1-10 μm, so that the first negative electrode and the negative electrode active material have good contact performance.

According to the present disclosure, the thicknesses of the conductor layer 12 and the insulating layer 13 may each vary within a wide range, for example, the thickness of the conductor layer 12 may be 0.1 to 50 μm, preferably 1 to 10 μm, and the thickness of the insulating layer 13 may be 1 to 50 μm, preferably 1 to 10 μm.

According to the present disclosure, the conductor layer 12 and the insulating layer 13 may be integrally formed by means of bonding, gluing, hot press molding, or the like, or a first organic porous separator material may be applied to one side of the conductor layer 12 in a coating manner to form the insulating layer 13.

According to the present disclosure, the material of the active material layer 11 may be one or more of natural graphite, artificial graphite, hard carbon, soft carbon, lithium titanate, iron oxide, lithium titanium phosphate, titanium dioxide, silicon oxide, aluminum, tin, and antimony. The material of the active material layer 11 is preferably a lithium intercalation material with an electrode potential higher than that of lithium, such as graphite, soft carbon, hard carbon, silicon oxide, tin, antimony, lithium titanate, so that when a large amount of lithium dendrites are generated in the second negative electrode 2 and penetrate through the insulating layer 13 and the conductor layer 12, possibly further contacting the active material layer 11, due to the difference of the electrode potentials, the metal lithium and the active material layer 11 form a primary battery in the presence of electrolyte, the metal lithium spontaneously acts as an anode, electrons are lost to form lithium ions, and the electrons and the lithium ions are completely intercalated into the active material layer 11, thereby ensuring that the metal lithium cannot form a short-circuit connection with the positive electrode under any condition, and further overcoming the risks of battery short circuit, fire explosion and the like caused by the growth of the lithium dendrites in the traditional battery structure.

According to the present disclosure, the second negative electrode 2 may be a common variety of substances for collecting current, and particularly, the structure of the second negative electrode 2 may be one or more of a non-conductive body (e.g., a sheet, a foil, a mesh material, etc., of polyethylene, polypropylene, polyvinyl chloride, polyamic acid, and non-woven fabric coated with conductive particles), a solid metal body (e.g., a metal foil, a metal sheet, a metal cloth, etc.), and a metal body having a porous structure, and the metal body having the porous structure may include at least one of a metal mesh, a metal foam, and a metal body having surface pores.

Further, the second anode 2 may be coated with a lithium coating layer, referring to fig. 3. The method for preparing the lithium coating layer may be well known to those skilled in the art, and in one embodiment, when the second negative electrode is formed with a non-conductive body having conductive protrusions, a solid metal body, and a metal body having a porous structure, such as a metal mesh, a metal foam, etc., metallic lithium may be dispersed in an organic solvent (such as hexane, etc.) and then uniformly coated on at least one side of the solid metal body, the metal mesh, or the metal foam; orOr the metal lithium can be heated to a molten state and directly coated on the surface of a solid metal body or poured into pores of a metal mesh or foam metal; electrochemical deposition of lithium metal, etc. may also be employed. The dosage of the lithium coating can be 0.026-2.6 mg/cm based on the second negative electrode per unit surface area²More preferably, the volume of coated lithium metal is such that it does not overflow the pores of the metal mesh or metal foam. Lithium is coated on the second negative electrode in advance, so that lithium consumed by SEI film formation and side reactions can be effectively supplemented, and the capacity and the cycle life of the lithium ion battery containing the repeating unit disclosed by the invention can be further improved.

The metal body having a porous structure refers to a structure obtained by combining a solid structure with a porous structure, and may include a solid metal portion and a porous metal portion, and the porous metal portion is adjacent to the insulating layer 13. The method for preparing the metal body having a porous structure may be well known to those skilled in the art, and for example, the porous metal portion having a certain depth of pores may be formed on at least one side of the metal body by etching in situ, or the metal having a porous structure and the non-porous base metal may be physically pressed and integrated into a whole or may be bonded and fired into a whole ex situ.

In one embodiment, the metal body having surface pores may have micropores, for example, in one embodiment, the metal body having surface pores may have two major surfaces perpendicular to the stacking direction, at least one of which may have micropores formed thereon. Wherein, the metal body with surface pores can be obtained by forming micropores with certain depth on the non-porous base metal through corrosion by methods of in-situ generation, chemical and physical deposition, corrosion generation and the like. For example, a micron copper or copper alloy foil is adopted, and a certain thickness of porous metal copper or carbon is respectively deposited on the two side surfaces of the micron copper or copper alloy foil by a physical vapor deposition method (PVD) or a chemical vapor deposition method (CVD); or, the micron copper or copper alloy foil is put into an acid or alkaline chemical corrosive liquid and corroded for a certain time, so that corrosion holes are formed on two sides of the micron copper or copper alloy foil.

In another preferred embodiment, referring to fig. 4, the metal body having the surface pores may include a first porous portion 21, a solid metal portion 22, and a second porous portion 23 sequentially arranged in the lamination direction, i.e., the first porous portion 21 and the second porous portion 23 are located at both sides of the solid metal portion 22. The first porous portion 21 and/or the second porous portion 23 may have through holes extending in the lamination direction, and preferably, the first porous portion 21 and the second porous portion 23 may have through holes extending in the lamination direction, respectively. The through-hole can effectively provide a space for accommodating metallic lithium, thereby further improving battery capacity. In addition, the porous structure can provide more reaction sites, which is beneficial to improving the rate performance of the battery. This embodiment is particularly suitable for lithium ion batteries having a multiple negative electrode structure.

Further, the solid metal part 22 may be a solid metal body (e.g., a metal foil, a metal sheet, a metal cloth, etc.). The thickness of the solid metal part 22 may be 1 to 50 μm, preferably 5 to 15 μm. The first porous portion 21 and the second porous portion 23 may be a porous metal material, a porous carbon material, or a porous oxide material, such as a copper mesh or a copper foam, respectively. The first porous portion 21 and the second porous portion 23 may each have a thickness of 1 to 50 μm, preferably 5 to 15 μm. In this embodiment, the first porous portion 21, the solid metal portion 22, and the second porous portion 23 may be stacked in this order and then connected to be integrated by physical press-fitting, or may be bonded and fired to be integrated, thereby obtaining a metal body having surface pores. For example, in one embodiment, a copper mesh (or foam copper), a copper foil, and a copper mesh (or foam copper) may be sequentially welded into a whole by superimposing current, so as to obtain a metal body having surface pores.

Further, according to the present disclosure, the hole diameter of the through-hole of the first porous portion 21 may be gradually expanded in the lamination direction, and the hole diameter of the through-hole of the second porous portion 23 may be constant in the lamination direction. Alternatively, the hole diameter of the through-hole of the first porous portion 21 may be constant in the stacking direction, and the hole diameter of the through-hole of the second porous portion 23 may be tapered in the stacking direction. In a preferred embodiment, the through-holes of the first porous portion 21 have a diameter that gradually widens in the stacking direction, and the through-holes of the second porous portion 23 have a diameter that gradually tapers in the stacking direction. The first and second porous portions 21 and 23 having the through-holes may be prepared by a conventional process according to the kind thereof, for example, when the first and second porous portions 21 and 23 are porous metal materials, respectively, they are simply cut in a diagonal shape. In this embodiment, the through hole with such a shape can provide more deposition space for lithium, and at the same time, can more effectively inhibit and restrict the growth range of metal lithium, thereby not only providing sufficient capacity, but also avoiding safety problems such as short circuit caused by lithium dendrites.

Preferably, the through-hole may be filled with lithium, referring to fig. 5. Thus, when the positive electrode material does not contain lithium or the positive electrode system is mixed with a lithium-free material, the energy density of the battery can be further increased by lithium pre-filled in the through-holes. In addition, the lithium is deposited in advance, so that the consumption of active lithium caused by SEI film formation, side reaction and the like can be supplemented, and the capacity retention rate and the cycle life of the battery are improved. Lithium can be deposited into the through holes by means of pre-pressing, high-temperature casting, electrodeposition, evaporation and the like, and the lithium can exist in a powder form, a block form, a nanowire form and the like. The filling amount of lithium can be adjusted according to actual needs, and can be 0.026-2.6 mg/cm²。

In order to further achieve the purpose that the first negative electrode 1 and the second negative electrode 2 are in electrical contact with each other during charging, in the embodiment where the second negative electrode 2 is a metal body with a porous structure, a second organic porous separator material layer may be further included between the second negative electrode 2 and the insulating layer 13, and the second organic porous separator material layer is in close contact with the second negative electrode, so as to ensure that no electrical contact occurs between the first negative electrode and the second negative electrode, and the porous structure specially designed for the second negative electrode is provided, so that lithium can be grown in a dendrite-free morphology, and the growth behavior of lithium in the second negative electrode 2 is further limited. Meanwhile, the second organic porous membrane material layer can also avoid lithium deposition at the tip, so that lithium is completely deposited in the porous structure. The second organic porous separator material layer may be various separator material layers used in a lithium ion battery well known to those skilled in the art, and may be, for example, a layer formed of one or more of a porous PE (polyethylene) separator, a porous PP (polypropylene) separator, a porous PET (polyethylene terephthalate) separator, a porous PAN (polyacrylonitrile) separator, a porous PI (polyimide) separator, and a porous PVDF (polyvinylidene fluoride) separator. The material of the second organic porous membrane material layer may be the same as or different from the material of the first organic porous membrane material.

Preferably, a second diaphragm may be disposed between adjacent repeating units, and the material of the second diaphragm may be the same as or different from that of the first diaphragm.

When a plurality of lithium ion battery repeating units of the present disclosure are overlapped to form a lithium ion battery, first negative electrode tabs of different repeating units can be electrically connected together and form a first negative electrode tab of the lithium ion battery, second negative electrode tabs of different repeating units can be electrically connected together and form a second negative electrode tab of the lithium ion battery, and positive electrode tabs of different repeating units can be electrically connected together and form a positive electrode tab of the lithium ion battery.

In accordance with the present disclosure, the structure of a lithium ion battery may be conventional in the art, for example, a lithium ion battery may include a casing, a pole piece located inside the casing, and an electrolyte, the pole piece including a lithium ion battery repeat unit provided by the first aspect of the present disclosure.

The positive electrode of the lithium ion battery repeating unit of the present disclosure includes a positive electrode material, and the positive electrode material is not particularly limited. The positive electrode material may generally include a positive electrode active material, a binder, and a conductive agent. The positive electrode active material may be any material that has been commercially available so far, such as LiFePO₄、Li₃V₂(PO₄)₃、LiMn₂O₄、LiMnO₂、LiNiO₂、LiCoO₂、LiVPO₄F、LiFeO₂Etc.; or ternary system Li_1+xL_1－y－zM_yN_zO₂Wherein x is more than or equal to 0.1 and less than or equal to 0.2, 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, and y + z is more than or equal to 0 and less than or equal to 1.0, and L, M, N are at least one of Co, Mn, Ni, Al, Mg, Ga and 3d transition metal elements respectively and independently. Glue stickThe binder may be any binder known in the art, for example, one or more of polyvinylidene fluoride, polytetrafluoroethylene, styrene butadiene rubber, and polyacrylate may be used. The content of the binder may be 0.1 to 15 wt%, preferably 1 to 7 wt% of the positive electrode material. The conductive agent may be any conductive agent known in the art, and for example, one or more of graphite, carbon fiber, carbon black, metal powder, metal oxide, and fiber may be used. The content of the conductive agent may be 0.1 to 20% by weight, preferably 1 to 5% by weight, of the positive electrode material. The method for preparing the positive electrode can adopt various methods commonly used in the field, for example, a positive electrode active material, a binder and a conductive agent are prepared into a positive electrode material slurry by using a solvent, the adding amount of the solvent is well known to those skilled in the art, and the solvent can be flexibly adjusted according to the viscosity and operability requirements of the slurry coating of the prepared positive electrode slurry. And then coating the prepared positive material slurry on a positive current collector, drying and tabletting, and cutting into pieces to obtain the positive electrode and the negative electrode. The drying temperature can be generally 120 ℃ and the drying time is generally 5 h. The solvent used in the positive electrode slurry may be any of various solvents known in the art, such as one or more selected from water, N-methylpyrrolidone (NMP), Dimethylformamide (DMF), Diethylformamide (DEF), Dimethylsulfoxide (DMSO), Tetrahydrofuran (THF), and alcohols. The solvent is used in an amount such that the slurry can be applied to the conductive substrate. Generally, the solvent is used in an amount such that the content of the positive electrode active material in the slurry is 40 to 90% by weight, preferably 50 to 85% by weight.

The positive electrode current collector is well known to those skilled in the art in light of the present disclosure, and generally, an aluminum foil may be used, and the thickness may be 1 to 50 μm, preferably 5 to 15 μm. The carbon-coated aluminum foil can also be used, wherein the thickness of the carbon coating is 0.1-10 μm, preferably 1-5 μm, and the coated carbon material can be one or more of commercial graphite, hard carbon, soft carbon, mesocarbon microbeads, carbon nanotubes, graphene and carbon fibers.

In accordance with the present disclosure, the first separator of the repeating unit of the lithium ion battery of the present disclosure has an electrical insulation property, and the kind thereof may be selected from various separators used in lithium ion batteries known to those skilled in the art, such as a polyolefin microporous film, polyethylene terephthalate, polyethylene felt, glass fiber felt, or ultra fine glass fiber paper.

According to the present disclosure, the electrolyte may be a solution of an electrolytic lithium salt in a non-aqueous solvent, and the electrolytic lithium salt may be selected from, for example, lithium hexafluorophosphate (LiPF)₆) Lithium perchlorate (LiClO)₄) Lithium tetrafluoroborate (LiBF)₄) Lithium hexafluoroarsenate (LiAsF)₆) Lithium hexafluorosilicate (LiSiF)₆) Lithium tetraphenylborate (LiB (C)₆H₅)₄) Lithium chloride (LiCl), lithium bromide (LiBr), lithium chloroaluminate (LiAlCl)₄) Fluorine fluorosulfonic acid lithium (LiC (SO)₂CF₃)₃)、LiCH₃SO₃、LiN(SO₂CF₃)₂And LiN (SO)₂C₂F₅)₂One or more of them. The non-aqueous solvent can be a mixed solution of chain ester and cyclic ester, wherein the chain ester can be one or more of dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), Methyl Propyl Carbonate (MPC), dipropyl carbonate (DPC) and other chain organic esters containing fluorine, sulfur or unsaturated bonds; the cyclic acid ester can be one or more of Ethylene Carbonate (EC), Propylene Carbonate (PC), Vinylene Carbonate (VC), gamma-butyrolactone (gamma-BL), sultone and other cyclic organic esters containing fluorine, sulfur or unsaturated bonds. The non-aqueous solvent can also be a solution or a mixed solution of chain ether and cyclic ether, wherein the cyclic ether can be one or more of Tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-MeTHF), 1, 3-Dioxolane (DOL), 4-methyl-1, 3-dioxolane (4-MeDOL) and other chain organic esters containing fluorine, sulfur or unsaturated bonds; the chain ether mainly comprises one or more of Dimethoxymethane (DMM), 1, 2-Dimethoxyethane (DME), 1, 2-Dimethoxypropane (DMP), Diglyme (DG) and other chain organic esters containing fluorine, sulfur or unsaturated bonds. In the electrolyte, the concentration of the electrolyte lithium salt is generally 0.1 to 15mol/L, preferably 1 to 10 mol/L.

Generally, the lithium ion battery repeating unit provided by the first aspect of the present disclosure is made into a pole core according to a method known in the art, for example, the lithium ion battery repeating unit is made into a pole core by a method such as winding or lamination, and then the pole core is placed into a battery case, an electrolyte is added, and the battery case is sealed to obtain the lithium ion battery. The sealing method and the amount of the electrolyte are known to those skilled in the art.

A third aspect of the disclosure: there is provided a method of using a lithium ion battery provided in a second aspect of the present disclosure, the method comprising the steps of: when charging, the second cathode 2 is charged until the battery capacity reaches Y, and then the first cathode 1 is switched to be charged until the battery capacity reaches Y + X.

Wherein, when the second negative electrode 2 is charged until the battery capacity reaches Y, the negative electrode capacity Y is derived from the deposition reaction of lithium on the second negative electrode; when the first negative electrode 1 is charged until the battery capacity reaches Y + X, the negative electrode capacity X is derived from an intercalation reaction or alloying reaction of lithium in the first negative electrode. The method disclosed by the invention enables the amount of the generated metal lithium during charging to be only filled and concentrated between the insulating layer and the second negative electrode, and lithium dendrite puncture can not occur, so that the short circuit risk in the traditional battery structure is overcome.

Further, the above-described charging process may be controlled using a charging control element, which may be conventionally employed by those skilled in the art, and may be, for example, a BMS (battery management system device).

During discharging, there is no limitation, the first negative electrode and the second negative electrode may be separately connected to the positive electrode for discharging, or the first negative electrode and the second negative electrode may be connected in parallel as the negative electrode to be connected to the positive electrode for discharging. The sum of X and Y depends on the electrochemical capacity of the positive electrode corresponding to the total lithium ion available for extraction.

The present disclosure is described in further detail below by way of examples of embodiments and with reference to the accompanying drawings.

Example 1

1. Preparing a positive electrode: weighing the positive electrode active material (LiCoO)₂) Adding 1kg of conductive agent carbon nano tube 20g and binder polyvinylidene fluoride (PVDF)20g into 1kg of N-methyl pyrrolidone, and then stirring in a stirrer for 30min to form stable and uniform slurry; uniformly coating the slurry on an aluminum foil, and drying in an oven at 80 ℃; after the dried pole piece is subjected to wondering under the pressure of 2MPa, the pole piece is cut into a pole piece with the thickness of 50mm multiplied by 75mm, a positive pole lug is subjected to spot welding, and the surface density is 30mg/cm²。

2. Preparing a diaphragm: a common commercial 11 μm PVDF coated lithium battery PE separator was cut into 77mm wide pieces.

3. Preparing a first negative electrode: a common commercial 11 mu m PVDF coated lithium battery PE diaphragm (an insulating layer) and a copper net (a conductor layer) with the thickness of 20 mu m are taken to be hot-pressed for 30s at the temperature of 120 ℃, the pressure is 1MPa, the porosity of the copper net is 50 percent, and the pore diameter is 1 mm. Weighing 1kg of negative active material (15 mu m of artificial graphite and silicon oxide composite negative material D50), 10g of conductive agent acetylene black, 30g of binder Styrene Butadiene Rubber (SBR) and 20g of sodium carboxymethylcellulose (CMC) and adding the materials into 1kg of deionized water, and then stirring the materials in a stirrer to form stable and uniform slurry; uniformly coating the slurry on the surface of the conductor layer, and then drying in an oven at 80 ℃; after the dried pole piece is subjected to wondering under the pressure of 2MPa, the pole piece is cut into a pole piece with the thickness of 50mm multiplied by 75mm, a first negative pole tab is subjected to spot welding, and the surface density is 10mg/cm²。

4. Preparing a second negative electrode: and cutting a common commercial 8-micron copper foil into a pole piece of 50cm multiplied by 75cm, and spot-welding a second negative pole tab.

5. Assembling the battery: assembling the manufactured positive electrode, diaphragm, first negative electrode (one side of the active material layer faces the diaphragm, one side of the insulating layer faces the second negative electrode) and second negative electrode in sequence according to a laminated battery process, and then packaging the assembled positive electrode, diaphragm, first negative electrode and second negative electrode in an aluminum plastic film; and filling the electrolyte, connecting the positive electrode lug and the first negative electrode lug, forming, and then performing air exhaust, heat sealing, edge folding and other process links to obtain the lithium ion battery, wherein the total thickness of the battery is 4 mm.

6. Testing the charge and discharge performance of the battery: the first negative electrode and the second negative electrode are connected to a charge control element (BMS), and a positive electrode tab and a second negative electrode tab are connected at a rate of 5mA/cm²Charging for 24min at constant current with the charging capacity of 1.6 Ah; then disconnecting the positive electrode tab and the first negative electrode tab, and switching the positive electrode tab and the first negative electrode tab to 5mA/cm²Current constant-current charging, the cut-off voltage is 4.4V, and the charging capacity is 2.8 Ah; the total charge capacity of the two stages was 4.4 Ah. After the first negative electrode tab and the second negative electrode tab are connected in parallel, the discharge current is 5mA/cm²The discharge cut-off voltage was 2.75V, and the total discharge capacity was 4.1 Ah.

Example 2

1. A positive electrode and a separator were prepared according to the method of example 1.

2. Preparing a first negative electrode: weighing 20g of PVDF-HFP, dissolving in 80g of acetone, adding 3g of ethanol as a pore-forming agent, uniformly dispersing, coating on one side of a copper mesh (conductor layer) with the thickness of 15 microns by a blade coating method, and drying in a vacuum oven at 60 ℃ for 8 hours, wherein the porosity of the copper mesh is 60%, the pore diameter is 1mm, and the thickness of the PVDF coating (insulating layer) is 4 microns. Weighing 1kg of negative active material (D50 is a 2 mu m silicon oxide and carbon nano tube composite negative material), 10g of conductive agent acetylene black, 30g of binder Styrene Butadiene Rubber (SBR) and 20g of sodium carboxymethylcellulose (CMC) and adding the materials into 1kg of deionized water, and then stirring the materials in a stirrer to form stable and uniform slurry; uniformly coating the slurry on the surface of the conductor layer, and then drying in an oven at 80 ℃; after the dried pole piece is subjected to wondering under the pressure of 2MPa, the pole piece is cut into a pole piece with the thickness of 50mm multiplied by 75mm, a first negative pole tab is subjected to spot welding, and the surface density is 10mg/cm²。

3. Preparing a second negative electrode: taking a common 15-micron copper-zinc alloy foil, immersing the common 15-micron copper-zinc alloy foil in a 1M NaOH solution for 1h, taking out the common 15-micron copper-zinc alloy foil, washing the common 15-micron copper-zinc alloy foil with deionized water, and drying the common 15-micron copper-zinc alloy foil to obtain a structure with a first porous part 21, a solid metal part 22 and a second porous part 23 as shown in figure 4; the first porous portion 21 and the second porous portion 23 each had a hole depth of 5 μm, and the intermediate solid metal portion 22 was cut into a pole piece of 50cm × 75cm in thickness, and the second negative electrode tab was spot-welded.

4. Assembling the battery: assembling the manufactured positive electrode, diaphragm, first negative electrode (one side of the active material layer faces the diaphragm, one side of the insulating layer faces the second negative electrode) and second negative electrode in sequence according to a laminated battery process, and then packaging the assembled positive electrode, diaphragm, first negative electrode and second negative electrode in an aluminum plastic film; and filling the electrolyte, connecting the positive electrode lug and the first negative electrode lug, forming, and then performing air exhaust, heat sealing, edge folding and other process links to obtain the lithium ion battery, wherein the total thickness of the battery is 4 mm.

5. Testing the charge and discharge performance of the battery: the first negative electrode and the second negative electrode are connected on a charging control element BMS, and a positive electrode tab and a second negative electrode tab are connected firstly at 6mA/cm²Charging for 24min at constant current with the charging capacity of 2.2 Ah; then disconnecting the positive electrode tab and the first negative electrode tab, and switching the positive electrode tab and the first negative electrode tab to 6mA/cm²Current constant-current charging, the cut-off voltage is 4.1V, and the charging capacity is 3.6 Ah; the total capacity of the two-stage charging is 5.8 Ah. After the first negative electrode tab and the second negative electrode tab are connected in parallel, the discharge current is 5mA/cm²The discharge cut-off voltage was 2.75V, and the total discharge capacity was 5.1 Ah.

Example 3

1. Preparing a positive electrode: weighing positive electrode active material (LiFePO)₄) Adding 1kg of NMP into 20g of conductive agent carbon nano tube and 10g of binder polyvinylidene fluoride (PVDF), and stirring for 30min in a stirrer to form stable and uniform slurry; uniformly coating the slurry on an aluminum foil, and drying in an oven at 80 ℃; after the dried pole piece is subjected to wondering under the pressure of 2MPa, the pole piece is cut into a pole piece with the thickness of 50mm multiplied by 75mm, a positive pole lug is subjected to spot welding, and the surface density is 10mg/cm²。

3. Preparing a first negative electrode: a common commercial 11 mu m PVDF coated lithium battery PE diaphragm (an insulating layer) and a porous carbon cloth (a conductor layer) with the thickness of 20 mu m are taken to be hot-pressed for 30s at the temperature of 120 ℃, the pressure is 1MPa, the porosity of the porous carbon cloth is 50 percent, and the pore diameter is 1 mm. 1kg of negative active material (15 mu m of artificial graphite and silicon oxide composite negative material with D50), 10g of conductive agent acetylene black, 30g of binder Styrene Butadiene Rubber (SBR) and 20g of sodium carboxymethylcellulose (CMC) are weighed and added into 1kg of deionized water, and then stirred in a stirrer to form stable and uniform slurry(ii) a Uniformly coating the slurry on the surface of the conductor layer, and then drying in an oven at 80 ℃; rolling the dried pole piece under the pressure of 2MPa, cutting into pole pieces of 50mm multiplied by 75mm, spot-welding a first negative pole tab, wherein the surface density is 10mg/cm²。

4. Preparing a second negative electrode: taking a common 15-micron copper-zinc alloy foil, immersing the common 15-micron copper-zinc alloy foil in a 1M NaOH solution for 1h, taking out the common 15-micron copper-zinc alloy foil, washing the common 15-micron copper-zinc alloy foil with deionized water, and drying the common 15-micron copper-zinc alloy foil to obtain a structure with a first porous part 21, a solid metal part 22 and a second porous part 23 as shown in figure 4; the first porous portion 21 and the second porous portion 23 each had a hole depth of 10 μm and a thickness of the intermediate solid metal portion 22 of 5 μm, and then both surfaces were coated with a metal lithium layer having a thickness of 5 μm under vacuum, the electrode sheet was subjected to wove pressing under a pressure of 0.5MPa, cut into a 50cm × 75cm electrode sheet, and a second negative electrode tab was spot-welded.

5. Assembling the battery: assembling the manufactured anode, diaphragm, first cathode (one side of the active material layer faces the diaphragm, one side of the insulating layer faces the second cathode) and second cathode in sequence according to a laminated battery process, and then packaging in a 50-micrometer-thick toughened film; and filling the electrolyte, connecting the positive electrode lug and the first negative electrode lug, forming, and then performing air exhaust, heat sealing, edge folding and other process links to obtain the lithium ion battery, wherein the total thickness of the battery is 4 mm.

6. Testing the charge and discharge performance of the battery: the first negative electrode and the second negative electrode are connected to a charge control element BMS, and a positive electrode tab and a second negative electrode tab are connected with a voltage of 1.5mA/cm²Charging for 15min at constant current with the charging capacity of 1.0 Ah; then disconnecting the positive electrode tab and the first negative electrode tab, and switching the positive electrode tab and the first negative electrode tab to be 1.5mA/cm²Current constant-current charging, the cut-off voltage is 3.8V, and the charging capacity is 2.2 Ah; the total capacity of the two-stage charging is 3.2 Ah. After the first negative electrode tab and the second negative electrode tab are connected in parallel, the discharge current is 1.5mA/cm²The discharge cut-off voltage was 2.0V, and the total discharge capacity was 3.04 Ah.

Example 4

1. Preparing a positive electrode: weighing the positive electrode active material (LiCoO)₂)1kg of conductive agent carbon nano tube 20g and binder polyvinylidene fluoride (PVDF)20g are added into 1kg of N-methyl pyrrolidone, and then stirred in a stirrer for 30min to formStabilizing the homogeneous slurry; uniformly coating the slurry on an aluminum foil, and drying in an oven at 80 ℃; after the dried pole piece is subjected to wondering under the pressure of 2MPa, the pole piece is cut into a pole piece with the thickness of 50mm multiplied by 75mm, a positive pole lug is subjected to spot welding, and the surface density is 30mg/cm²。

3. Preparing a first negative electrode: 100g of indium tin oxide particles are mixed with 5g of PVDF and 200g of NMP solution and stirred uniformly, then coated on a common commercial 10-micron lithium battery PE diaphragm (insulating layer), and then hot-pressed at 110 ℃ for 20min under the pressure of 1 MPa. Weighing 1kg of negative active material (15 mu m of artificial graphite and silicon oxide composite negative material D50), 10g of conductive agent acetylene black, 30g of binder Styrene Butadiene Rubber (SBR) and 20g of sodium carboxymethylcellulose (CMC) and adding the materials into 1kg of deionized water, and then stirring the materials in a stirrer to form stable and uniform slurry; uniformly coating the slurry on the surface of the conductive oxide, and then drying in an oven at 80 ℃; after the dried pole piece is subjected to wondering under the pressure of 2MPa, the pole piece is cut into a pole piece with the thickness of 50mm multiplied by 75mm, a first negative pole tab is subjected to spot welding, and the surface density is 10mg/cm²。

6. Testing the charge and discharge performance of the battery: the first negative electrode and the second negative electrode are connected to a charge control element (BMS), and a positive electrode tab and a second negative electrode tab are connected at a rate of 5mA/cm²Charging for 24min at constant current with the charging capacity of 1.6 Ah; then disconnecting the positive electrode tab and the first negative electrode tab, and switching the positive electrode tab and the first negative electrode tab to 5mA/cm²Charging with constant current and stoppingThe voltage is 4.4V, and the charging capacity is 2.8 Ah; the total charge capacity of the two stages was 4.4 Ah. After the first negative electrode tab and the second negative electrode tab are connected in parallel, the discharge current is 5mA/cm²The discharge cut-off voltage was 2.75V, and the total discharge capacity was 4.05 Ah.

Example 5

4. Preparing a second negative electrode: taking 30-micron-thick foamy copper with the porosity of 75%, evaporating a 3-micron-thick metal lithium layer on two sides of the foamy copper by using a vacuum evaporation method, performing wove pressing on a pole piece under the pressure of 0.5MPa, cutting the pole piece into a pole piece of 50cm multiplied by 75cm, and performing spot welding on a second negative pole tab.

6. Testing the charge and discharge performance of the battery: the first negative electrode and the second negative electrode are connected to a charge control element (BMS), and a positive electrode tab and a second negative electrode tab are connected at a rate of 5mA/cm²Charging for 24min at constant current with the charging capacity of 1.6 Ah; then disconnecting the positive electrode tab and the first negative electrode tab, and switching the positive electrode tab and the first negative electrode tab to 5mA/cm²Current constant-current charging, the cut-off voltage is 4.4V, and the charging capacity is 2.8 Ah; the total charge capacity of the two stages was 4.4 Ah. After the first negative electrode tab and the second negative electrode tab are connected in parallel, the discharge current is 5mA/cm²The discharge cut-off voltage was 2.75V, and the total discharge capacity was 4.3 Ah.

Comparative example 1

2. Preparing a negative electrode: weighing 1kg of negative active material (artificial graphite with 15 mu m of D50), 10g of conductive agent acetylene black, 30g of binder Styrene Butadiene Rubber (SBR) and 20g of sodium carboxymethylcellulose (CMC), adding the materials into 1kg of deionized water, and stirring in a stirrer to form stable and uniform slurry; uniformly coating the slurry on the surface of a copper foil with the thickness of 8 mu m, and then transferring the copper foil into an oven to be dried at the temperature of 80 ℃; after the dried pole piece is subjected to wondering under the pressure of 2MPa, the pole piece is cut into a pole piece with the thickness of 50mm multiplied by 75mm, a negative pole tab is subjected to spot welding, and the surface density is 14mg/cm²。

3. Assembling the battery: assembling the manufactured positive electrode, diaphragm and negative electrode in sequence according to a laminated battery process, and then packaging in an aluminum plastic film; and filling the electrolyte, connecting the positive electrode lug and the first negative electrode lug, forming, and then performing air exhaust, heat sealing, edge folding and other process links to obtain the lithium ion battery, wherein the total thickness of the battery is 4 mm.

4. Testing the charge and discharge performance of the battery: the formed battery is measured at 5mA/cm²Charging for 60min at constant current, with cut-off voltage of 4.4V and charging capacity of 3.7 Ah; then at 1.5mA/cm²The current is discharged in a constant current, the discharge cut-off voltage is 3.3V, and the total discharge capacity is 3.4 Ah.

Comparative example 2

1. Preparing a positive electrode: weighing positive electrode active material (LiFePO)₄) Adding 1kg of conductive agent carbon nano tube 20g and binder polyvinylidene fluoride (PVDF)20g into 1kg of N-methyl pyrrolidone, and then stirring in a stirrer for 30min to form stable and uniform slurry; uniformly coating the slurry on an aluminum foil, and drying in an oven at 80 ℃; after the dried pole piece is subjected to wondering under the pressure of 2MPa, the pole piece is cut into a pole piece with the thickness of 50mm multiplied by 75mm, a positive pole lug is subjected to spot welding, and the surface density is 15mg/cm²。

3. Preparing a negative electrode: weighing 1kg of negative active material (artificial graphite with 15 mu m of D50), 10g of conductive agent acetylene black, 30g of binder Styrene Butadiene Rubber (SBR) and 20g of sodium carboxymethylcellulose (CMC), adding the materials into 1kg of deionized water, and stirring in a stirrer to form stable and uniform slurry; uniformly coating the slurry on the surface of a copper foil with the thickness of 8 mu m, and then transferring the copper foil into an oven to be dried at the temperature of 80 ℃; after the dried pole piece is subjected to wondering under the pressure of 2MPa, the pole piece is cut into a pole piece with the thickness of 50mm multiplied by 75mm, a negative pole tab is subjected to spot welding, and the surface density is 7mg/cm²。

4. Assembling the battery: assembling the manufactured positive electrode, diaphragm and negative electrode in sequence according to a laminated battery process, placing a 40mm multiplied by 10mm lithium sheet on the outer side of the laminated battery core, leading out a single tab as a reference electrode interface, and then packaging the whole battery core including the reference electrode in an aluminum-plastic film; and filling the electrolyte, and performing technological links such as air extraction, heat sealing, edge folding treatment and the like after formation to obtain the lithium ion battery, wherein the total thickness of the battery is 4 mm.

5. Testing the charge and discharge performance of the battery: the formed battery is heated to 1.5mA/cm²Charging for 60min at constant current, with cut-off voltage of 3.8V and charging capacity of 2.4 Ah; then at 1.5mA/cm²The current is discharged in a constant current, the discharge cut-off voltage is 2V, and the total discharge capacity is 2.2 Ah.

Comparative example 3

1. A positive electrode and a separator were prepared according to the method of comparative example 2.

2. Preparing a negative electrode: the copper foil 8 μm thick was cut into 50mm × 75mm pieces, and the negative electrode tab was spot-welded.

4. Testing the charge and discharge performance of the battery: the formed battery is heated to 1.5mA/cm²Charging for 60min at constant current, with cutoff voltage of 3.8V and charging capacity of 3.6 Ah; then at 1.5mA/cm²The current is discharged in a constant current, the discharge cut-off voltage is 2V, and the total discharge capacity is 3.0 Ah.

Test example 1

The lithium ion batteries prepared in examples and comparative examples were tested for discharge capacity, energy density, and cycle performance, and the results are shown in table 1.

The circulating method comprises the following steps: and (4) carrying out constant-current charging and discharging on the battery, and calculating the capacity retention rate after multiple cycles. The energy density test method comprises the following steps: and recording the discharge voltage, the discharge capacity and the battery volume of the battery, wherein the energy density of the battery is the discharge voltage multiplied by the discharge capacity divided by the battery volume. The charging efficiency and capacity retention rate were calculated according to the following formulas.

Charge efficiency (%) -discharge capacity/charge capacity

Capacity retention (%) (discharge capacity at n-th cycle/discharge capacity at 1 st cycle)

TABLE 1

Test example 2

The battery of comparative example 2 was subjected to a charge-discharge test at 1.5mA/cm²Charging for 60min at constant current, and cutting off the voltage to 3.8V; then at 1.5mA/cm²The current discharges in constant current, and the discharge cut-off voltage is 2V. To pairThe battery of the ratio 3 was short-circuited after 3 cycles, and the appearance of the battery was observed by a field emission scanning electron microscope (JSM-7600F, JEOL Ltd., Japan) after disassembling the battery, and the SEM photograph is shown in FIG. 6. It can be seen that a large amount of lithium dendrites are generated at the negative electrode side, causing short circuit to occur.

Test example 3

The cell prepared in comparative example 2 was charged at 1.5mA/cm²The current was measured for charge and discharge with a cut-off voltage of 3.8V and a cut-off voltage of 2V, and the positive-negative voltage curve, the positive-reference voltage curve and the negative-reference voltage curve were measured during discharge, respectively, as shown in fig. 7. As can be seen from fig. 7, in the discharge state, the voltage (vs. li) of the conventional anode (equivalent to the first anode in the battery of example 3) at this time⁺,/Li) was 1.2V.

The cell of example 3 was discharged (at this time the first negative electrode 1 voltage was 1.2V (vs⁺Li), the second negative electrode voltage is 0V (Vs⁺/Li)) was connected to the positive electrode tab and the second negative electrode tab at 1.5mA/cm²Charging with constant current for 30min, charging total capacity for 2.0Ah, and standing for 15 min. During the charging process and during the standing process after stopping charging, respectively recording a first cathode-second cathode voltage curve, a positive electrode-second cathode voltage curve and a positive electrode-first cathode voltage curve, as shown in fig. 8-9. From the voltage change curves shown in FIGS. 8 to 9, it can be seen that the micropores (lithium thickness of 5 μm/cm) on the surface of the second negative electrode have been completely filled due to the volume of the generated metallic lithium after charging for more than 15min²) Thus, metallic lithium starts to grow along the pores in the first negative electrode until 16min, and the generated lithium dendrites penetrate the first negative electrode, resulting in a sudden drop of the first negative electrode-second negative electrode voltage from 1.2V to 0V; meanwhile, the voltage of the anode and the second cathode is also increased from 2.3V to 3.5V. Charging is continued to 30min, and then a large amount of lithium dendrites are generated and are fully communicated with the first negative electrode and the second negative electrode, but in a subsequent standing curve, the voltage of the positive electrode and the second negative electrode is reduced to 3.3V after 1min of standing, and the voltage of the first negative electrode and the second negative electrode is increased from 0 to 0.2V, which indicates that the lithium dendrites communicated with the first negative electrode and the second negative electrode are automatically disconnected.

Test example 4

The batteries of examples and comparative examples were tested for volume expansion after charging and discharging, and the results are shown in table 2.

The test method comprises the following steps: testing the battery in the initial state (h)₁) And in the fully charged state (h)₂) Thickness of (a), expansion ratio of (h)₂-h₁)/h₁。

TABLE 2

	Volume expansion ratio (% by unit)
		Example 1	12
Example 2	7
		Example 3	8
Example 4	12
		Example 5	8
Comparative example 1	9
		Comparative example 2	8
Comparative example 3	30

The preferred embodiments of the present disclosure are described in detail with reference to the accompanying drawings, however, the present disclosure is not limited to the specific details of the above embodiments, and various simple modifications may be made to the technical solution of the present disclosure within the technical idea of the present disclosure, and these simple modifications all belong to the protection scope of the present disclosure.

It should be noted that, in the foregoing embodiments, various features described in the above embodiments may be combined in any suitable manner, and in order to avoid unnecessary repetition, various combinations that are possible in the present disclosure are not described again.

In addition, any combination of various embodiments of the present disclosure may be made, and the same should be considered as the disclosure of the present disclosure, as long as it does not depart from the spirit of the present disclosure.

Claims

1. A lithium ion battery repeating unit, characterized in that the repeating unit comprises a positive electrode (3), a first separator (4) and a negative electrode which are stacked in this order in a stacking direction, the negative electrode comprising a first negative electrode (1) and a second negative electrode (2) which are in electrical contact with each other when charged; the first negative electrode (1) comprises an active material layer (11), a conductor layer (12) and an insulating layer (13); in the negative electrode, the active material layer (11), the conductor layer (12), the insulating layer (13), the second negative electrode (2), the insulating layer (13), the conductor layer (12), and the active material layer (11) are sequentially stacked in the stacking direction;

wherein the conductor layer (12) contains an inorganic porous conductive material, and liquid electrolyte is filled in pores of the inorganic porous conductive material;

the second negative electrode (2) is one or more of a non-conductive body formed with a conductive protrusion, a solid metal body, a metal body having a porous structure, a non-conductive body coated with a lithium coating layer and a conductive protrusion, a solid metal body coated with a lithium coating layer and a metal body having a porous structure coated with a lithium coating layer.

2. A repeating unit as claimed in claim 1, wherein the insulating layer (13) contains a first organic porous separator material.

3. The repeating unit according to claim 2, wherein the inorganic porous conductive material is one or more of a porous metal material, a porous carbon material and a porous oxide material.

4. The repeating unit of claim 3, wherein the porous metal material is a metal mesh or a metal foam; the porous metal material is one or more of copper, nickel, magnesium, aluminum, manganese, iron, titanium and zinc;

the porous carbon material is one or more of porous carbon spheres, porous carbon fibers, porous carbon nanotubes and porous carbon cloth;

the porous oxide material is a metal oxide or the metal oxide modified by doping; the metal oxide is selected from at least one of indium oxide, tin oxide, indium tin oxide, ruthenium dioxide, zinc oxide and silver oxide, and the doping element in the doped and modified metal oxide is at least one of carbon, boron, phosphorus, nitrogen, sulfur, selenium, chlorine, iodine and fluorine.

5. The repeating unit according to claim 2, wherein the first organic porous membrane material is one of a porous PE membrane, a porous PP membrane, a porous PET membrane, a porous PAN membrane, a porous PI membrane and a porous PVDF membrane, or a porous composite membrane formed of several of them.

6. The repeating unit as claimed in claim 2, wherein the pores of the first organic porous separator material are filled with a liquid electrolyte.

7. The repeating unit of claim 6, wherein the liquid electrolyte is one or more of an ester solution of a lithium salt, an ether solution, and a sulfone solution;

8. The repeating unit according to claim 1, wherein the surface of the conductor layer (12) contacting with the active material layer (11) is coated with a carbon coating, the carbon material of the carbon coating is one or more of graphite, hard carbon, soft carbon, mesocarbon microbeads, carbon nanotubes, graphene and carbon fibers, and the thickness of the carbon coating is 0.1-10 μm.

9. The repeating unit as claimed in claim 1, wherein the metal body having a porous structure includes at least one of a metal mesh, a metal foam, and a metal body having surface pores.

10. The repeating unit according to claim 1, wherein the amount of the lithium coating layer is 0.026-2.6 mg/cm based on the second negative electrode (2) per unit surface area²。

11. The repeating unit as recited in claim 9, wherein the metal body having the surface pores includes a first porous portion (21), a solid metal portion (22), and a second porous portion (23) which are provided in this order in the stacking direction, the first porous portion (21) and the second porous portion (23) each having a through hole extending in the stacking direction.

12. A repeating unit as claimed in claim 11, wherein the apertures of the through holes of the first porous portion (21) are flared in the stacking direction and the apertures of the through holes of the second porous portion (23) are tapered in the stacking direction.

13. The repeating unit as claimed in claim 11, wherein the through hole is filled with lithium.

14. The repeating unit as claimed in claim 1, wherein a second organic porous separator material layer is further included between the second negative electrode (2) and the insulating layer (13), the second organic porous separator material layer being a layer formed of one or more of a porous PE separator, a porous PP separator, a porous PET separator, a porous PAN separator, a porous PI separator, and a porous PVDF separator.

15. The repeating unit as claimed in claim 1, wherein the material of the active material layer (11) is one or more of natural graphite, artificial graphite, hard carbon, soft carbon, lithium titanate, iron oxide, lithium titanium phosphate, titanium dioxide, silicon oxide, aluminum, tin and antimony.

16. A lithium ion battery comprising one or more lithium ion battery repeating units according to any one of claims 1-15.

17. The lithium ion battery according to claim 16, wherein a second separator is provided between adjacent repeating units.

18. A method for using the lithium ion battery of claim 16 or 17, comprising the steps of: during charging, the second negative electrode (2) is charged until the battery capacity reaches Y, and then the first negative electrode (1) is charged until the battery capacity reaches Y + X.

19. A battery module characterized by comprising the lithium ion battery according to claim 16 or 17.

20. An automobile characterized by comprising the battery module according to claim 19.