CN113839080B - Lithium ion battery and preparation method thereof - Google Patents

Lithium ion battery and preparation method thereof Download PDF

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CN113839080B
CN113839080B CN202010590307.7A CN202010590307A CN113839080B CN 113839080 B CN113839080 B CN 113839080B CN 202010590307 A CN202010590307 A CN 202010590307A CN 113839080 B CN113839080 B CN 113839080B
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lithium
lithium alloy
alloy layer
magnesium
nonmetallic
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CN113839080A (en
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谢静
郭姿珠
马永军
吴荣方
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BYD 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
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/058—Construction or 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
    • H01M4/13—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
    • H01M4/36—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
    • H01M4/381—Alkaline or alkaline earth metals elements
    • H01M4/382—Lithium
    • 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
    • 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
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Abstract

The invention relates to the technical field of lithium ion batteries, in particular to a lithium ion battery and a preparation method thereof. The lithium ion battery comprises a positive electrode and a lithium alloy negative electrode, wherein the lithium alloy negative electrode comprises a first lithium alloy layer and a second lithium alloy layer arranged on the surface of the first lithium alloy layer, and the first lithium alloy layer is close to the positive electrode; the first lithium alloy layer and the second lithium alloy layer each contain a lithium element, a magnesium element and a nonmetallic element, wherein the nonmetallic element is at least one selected from N, F and S; wherein the mass ratio alpha of the nonmetallic element and the magnesium element in the first lithium alloy layer is larger than the mass ratio beta of the nonmetallic element and the magnesium element in the second lithium alloy layer. According to the invention, through the synergistic effect of the mass ratio of the nonmetallic element to the magnesium element, the generation of lithium dendrite in the lithium alloy negative electrode is effectively inhibited, and the structural stability and the safety performance of the lithium alloy negative electrode are improved, so that the high energy density and the cycle life of the lithium ion battery are improved.

Description

Lithium ion battery and preparation method thereof
Technical Field
The invention relates to the technical field of lithium ion batteries, in particular to a lithium ion battery and a preparation method thereof.
Background
Along with the wide application of the lithium ion battery in the fields of power, digital codes and the like, the lithium metal negative electrode has the advantages of high specific capacity (3860 mAh/g) and low reduction potential, is an ideal negative electrode material of the next-generation high-capacity lithium ion battery, but has low coulomb efficiency and safety caused by the problems of high reactivity of metal lithium, volume expansion in the circulating process, non-uniformity of deposition removal and the like, so that the lithium metal negative electrode is prevented from being practically applied in commercialization, and in addition, the self-supporting ultrathin metal lithium is difficult to realize due to the poor mechanical strength of the metal lithium.
There have been attempts by researchers to alloy lithium metal with other metals, such as Al, mg, sn, si, in, zn, to passivate the side reactions of lithium with the electrolyte and improve electrochemical cycle life. Jang look Choi et al (Advanced Energy Materials,2019, 1902278) reported that the electrochemical performance of a lithium magnesium alloy anode with a magnesium mass content of 5% was significantly better than that of a pure lithium anode, but from the scanning electron microscope results after lithium deposition, it is known that metallic lithium was deposited on the surface of the lithium magnesium alloy anode, and that a certain proportion of lithium dendrites began to form when the current density or the deposition capacity of lithium was increased. The relatively low diffusivity of lithium magnesium alloys makes metallic lithium vulnerable to deposition and dendrite formation on the alloy negative electrode surface.
Disclosure of Invention
The invention aims to solve the technical problem that lithium dendrites exist in a lithium ion battery cathode, and provides a lithium ion battery and a preparation method thereof, which can effectively inhibit the generation of lithium dendrites in a lithium alloy cathode and improve the structural stability and safety performance of the lithium alloy cathode, thereby improving the high energy density and the cycle life of the lithium ion battery.
In order to achieve the above object, a first aspect of the present invention provides a lithium ion battery including a positive electrode and a lithium alloy negative electrode, the lithium alloy negative electrode including a first lithium alloy layer and a second lithium alloy layer disposed on a surface of the first lithium alloy layer, the first lithium alloy layer being adjacent to the positive electrode;
the first lithium alloy layer and the second lithium alloy layer each contain a lithium element, a magnesium element and a nonmetallic element, wherein the nonmetallic element is at least one selected from N, F and S;
wherein the mass ratio alpha of the nonmetallic element and the magnesium element in the first lithium alloy layer is larger than the mass ratio beta of the nonmetallic element and the magnesium element in the second lithium alloy layer.
Preferably, in the first lithium alloy layer, the mass ratio α of the nonmetallic element to the magnesium element is 1.5-9:1, a step of; and/or, in the second lithium alloy layer, the mass ratio beta of the nonmetallic element and the magnesium element is 1:1.5-9.
The second aspect of the present invention provides a method for preparing a lithium ion battery, comprising the steps of:
(1)preparation of lithium alloy negative electrode：
A. Sequentially performing first sintering, first prepressing and first rolling on a first lithium source, a first non-metal source and a first magnesium source to obtain a first lithium alloy layer;
B. sequentially performing second sintering, second prepressing and second rolling on a second lithium source, a second non-metal source and a second magnesium source to obtain a second lithium alloy layer;
C. thirdly rolling the first lithium alloy layer and the second lithium alloy layer to obtain a lithium alloy anode;
(2)preparation of lithium ion batteries: assembling the lithium alloy negative electrode, the diaphragm and the positive electrode, wherein a first lithium alloy layer in the lithium alloy negative electrode is close to the positive electrode, so as to obtain a lithium ion battery;
or assembling the lithium alloy negative electrode, the solid electrolyte and the positive electrode, wherein a first lithium alloy layer in the lithium alloy negative electrode is close to the positive electrode, so as to obtain a lithium ion battery;
wherein the nonmetallic elements in the first nonmetallic source and the second nonmetallic source are each independently selected from at least one of N, F and S;
wherein the mass ratio alpha of the nonmetallic element and the magnesium element in the first lithium alloy layer is larger than the mass ratio beta of the nonmetallic element and the magnesium element in the second lithium alloy layer.
Preferably, the first non-metal source and the second non-metal source are each independently selected from a lithium-containing compound and/or a magnesium-containing compound comprising the non-metal element.
Compared with the prior art, the invention has the following advantages:
(1) The lithium alloy anode provided by the invention comprises a first lithium alloy layer and a second lithium alloy layer on the outer surface of the first lithium alloy layer, wherein the first lithium alloy layer has a higher mass ratio alpha of nonmetallic elements to magnesium elements, and the second lithium alloy layer has a lower mass ratio beta of nonmetallic elements to magnesium elements; according to the invention, through the synergistic effect of the mass ratio of the high nonmetallic element to the low nonmetallic element, the mass ratio of the magnesium element, the generation of lithium dendrites in the lithium alloy negative electrode is effectively inhibited, and the structural stability and the safety performance of the lithium alloy negative electrode are improved, so that the high energy density and the cycle life of the lithium ion battery are improved;
(2) The first lithium alloy layer provided by the invention has higher mass ratio alpha of nonmetallic elements and magnesium elements, and under relatively lower current density, metal lithium is diffused and is embedded into the second lithium alloy layer to form a lithium alloy solid solution structure, so that the generation of lithium dendrites is avoided, lower volume deformation is maintained, the stability of a lithium alloy negative electrode structure is improved, and the cycle life and high energy density of a lithium ion battery are improved; under relatively higher current density, as the nonmetallic element and the lithium element have better affinity, the nucleation energy of lithium can be reduced, more deposition sites are provided for the deposition of the metallic lithium, and the exchange current density of local deposition is reduced, so that the deposition of the metallic lithium is more compact and dendrite is not easy to form;
(3) According to the lithium alloy negative electrode provided by the invention, the mechanical strength, the ductility and the high energy density of the lithium alloy negative electrode are improved by changing the organization structure and the metallographic structure of lithium;
(4) The lithium alloy negative electrode provided by the invention has lower sensitivity to moisture in the air atmosphere, reduces the requirement on the environment, improves the safety performance of the lithium alloy negative electrode, reduces the production cost of a battery process, and is convenient for industrial production.
Drawings
FIG. 1 is a diagram showing a Li vs Li symmetrical cell PS1 of test example 1 at 0.5mA/cm 2 SEM images of 2h deposited lithium at current density;
FIG. 2 is a Li vs Li symmetrical battery PS1 of test example 1 at 1mA/cm 2 SEM images of 2h deposited lithium at current density.
Detailed Description
The endpoints and any values of the ranges disclosed herein are not limited to the precise range or value, and are understood to encompass values approaching those ranges or values. For numerical ranges, one or more new numerical ranges may be found between the endpoints of each range, between the endpoint of each range and the individual point value, and between the individual point value, in combination with each other, and are to be considered as specifically disclosed herein.
The first aspect of the invention provides a lithium ion battery, which comprises a positive electrode and a lithium alloy negative electrode, wherein the lithium alloy negative electrode comprises a first lithium alloy layer and a second lithium alloy layer arranged on the surface of the first lithium alloy layer, and the first lithium alloy layer is close to the positive electrode;
the first lithium alloy layer and the second lithium alloy layer each contain a lithium element, a magnesium element and a nonmetallic element, wherein the nonmetallic element is at least one selected from N, F and S;
wherein the mass ratio alpha of the nonmetallic element and the magnesium element in the first lithium alloy layer is larger than the mass ratio beta of the nonmetallic element and the magnesium element in the second lithium alloy layer.
In a preferred embodiment of the present invention, the mass ratio of the first lithium alloy layer to the second lithium alloy layer is 1:0.1 to 80, preferably 1:1-40. The adoption of the preferable mass ratio is more beneficial to improving the high energy density and long-life cycle performance of the lithium alloy cathode.
In the present invention, the nonmetallic elements in the first lithium alloy layer and the second lithium alloy layer are the same or different, and preferably, the nonmetallic elements in the first lithium alloy layer and the second lithium alloy layer are the same. With the preferred conditions, better cycle performance and smaller cycle volume deformation are achieved.
In the invention, the mass ratio alpha of the nonmetallic element and the magnesium in the first lithium alloy layer is high, and the high nonmetallic element is beneficial to guiding the deposition and diffusion of interfacial lithium due to the affinity between the nonmetallic element and lithium, so that lithium dendrite formation at the interface between the electrolyte and the lithium alloy negative electrode is effectively avoided; the mass ratio beta of nonmetallic elements and magnesium in the second lithium alloy layer is low, the second lithium alloy layer is mainly used for maintaining the volume deformation of a lithium alloy anode and providing enough supplementary lithium for the long-life cycle performance of a lithium ion battery, and because the magnesium element and the lithium element have certain bonding and adsorption effects, the lithium ion battery can absorb the stress effect caused by lithium intercalation, and meanwhile, the influence of magnesium on the deintercalability of lithium is small. Therefore, the first lithium alloy layer and the second lithium alloy layer realize dendrite-free lithium generation of the lithium alloy negative electrode through the mass ratio of different nonmetallic elements to magnesium elements, and the structural stability and the safety performance of the lithium alloy negative electrode are improved, so that the high energy density and the cycle life of the lithium ion battery are improved.
According to a preferred embodiment of the present invention, the nonmetallic elements in the first lithium alloy layer and the second lithium alloy layer are each N, and the N/Mg mass ratio α in the first lithium alloy layer is greater than the N/Mg mass ratio β in the second lithium alloy layer.
According to a preferred embodiment of the present invention, the nonmetallic elements in the first lithium alloy layer and the second lithium alloy layer are each F, and the mass ratio α of F/Mg in the first lithium alloy layer is greater than the mass ratio β of F/Mg in the second lithium alloy layer.
According to a preferred embodiment of the present invention, the nonmetallic elements in the first lithium alloy layer and the second lithium alloy layer are S, and the mass ratio α of S/Mg in the first lithium alloy layer is greater than the mass ratio β of S/Mg in the second lithium alloy layer.
In the invention, the inventor adjusts the mass ratio of nonmetallic elements and magnesium elements in the first lithium alloy layer and the second lithium alloy layer, so that the lithium alloy negative electrode can avoid the generation of lithium dendrites and the volume deformation of charge-discharge cycles under different current densities, and the mass ratio alpha of high nonmetallic elements and magnesium elements in the first lithium alloy layer and the mass ratio beta of low nonmetallic elements and magnesium elements in the second lithium alloy layer are guided by the affinity between interface nonmetallic-lithium and the coordination effect of internal lithium-magnesium bond energy adsorption, thereby effectively improving the structural stability and the safety performance of the lithium alloy negative electrode, and further improving the high energy density and the cycle performance of the lithium ion battery.
In the invention, under the condition that no special condition exists, the coordination effect refers to that the higher nonmetal element/magnesium mass ratio alpha in the first lithium alloy layer improves the affinity guiding between nonmetal elements and lithium and the diffusion capability of lithium ions in the alloy, the lower nonmetal element/magnesium mass ratio beta in the second lithium alloy layer can ensure the effect of lithium-magnesium bond adsorption during certain lithium ion diffusion, the relatively higher magnesium element can be beneficial to maintaining the structure of an alloy cathode, and the alloy cathode has almost no volume deformation during metal lithium intercalation and deintercalation of an alloy system, so the invention realizes the electrochemical behavior without lithium dendrite phenomenon under wider current density under the coordination effect of the affinity guiding between interface nonmetal elements with high nonmetal element/magnesium element mass ratio and internal lithium-magnesium bond adsorption, and improves the structural stability and the safety performance of the lithium alloy cathode, thereby improving the high energy density and the cycle performance of a battery.
According to the present invention, preferably, in the first lithium alloy layer, the mass ratio α of the nonmetallic element and the magnesium element is 1.5 to 9:1, preferably 2-8:1, a step of; further preferably, the mass content of the magnesium element in the first lithium alloy layer is 0.8% to 18% and the mass content of the nonmetallic element is 4.8% to 40.5% based on the total amount of the first lithium alloy layer. The adoption of the preferable conditions is favorable for avoiding the phenomenon of lithium dendrite caused by the deposition of metallic lithium on the surface under the low current density; at high current densities, the deposition of metallic lithium is promoted to be denser and less prone to dendrite formation.
Preferably, in the second lithium alloy layer, the mass ratio β of the nonmetallic element to the magnesium element is 1:1.5-9, preferably 1:2-8; further preferably, the mass content of the magnesium element in the second lithium alloy layer is 0.6 to 13.5% and the mass content of the nonmetallic element is 0.1 to 6% based on the total amount of the second lithium alloy layer. By adopting the preferable conditions, the consumption of lithium in the second lithium alloy layer is supplemented, and the frame structure of the lithium alloy anode can be maintained without causing the first lithium alloy layer to collapse due to the consumption of lithium.
In the present invention, the high current density and the low current density are relatively speaking without special description.
In the invention, as the high non-metal element/magnesium element mass ratio alpha in the first lithium alloy layer has higher electron conductivity and ion conductivity, under relatively lower current density, metal lithium is preferentially inserted into the second lithium alloy layer to avoid the formation of lithium dendrite, and meanwhile, the second lithium alloy layer has higher magnesium element content and a certain ion channel, thereby being beneficial to maintaining the structure of the lithium alloy anode and improving the structural stability of the lithium alloy anode; at a relatively high current density, the high non-metal element/magnesium element mass ratio alpha in the first lithium alloy layer provides more deposition sites for deposition of metal lithium, reduces the exchange current density of local deposition, and provides compactness of metal lithium deposition, so that the phenomenon of lithium dendrite is avoided, and meanwhile, when the second lithium alloy layer supplements the lithium alloy cathode, the framework structure of the lithium alloy cathode can be maintained due to the relatively high magnesium content.
According to the present invention, preferably, the lithium alloy negative electrode has a thickness of 1.5 to 50 μm, preferably 5 to 25 μm; the thickness of the first lithium alloy layer is 0.5-10 μm, preferably 0.6-2.5 μm; the thickness of the second lithium alloy layer is 1-40 μm, preferably 2.5-24 μm. The adoption of the preferable conditions is more beneficial to obtaining the comprehensive electrochemical performance with relatively balanced energy density and cycle life.
According to the present invention, preferably, the lithium alloy anode further comprises: and the surface of the current collector is sequentially provided with a second lithium alloy layer and a first lithium alloy layer.
Preferably, the current collector is selected from at least one of a porous metal, a graphene film, a carbon nanotube film, a carbon fiber film, and a polymer conductive film, and further preferably, the porous metal is selected from at least one of copper foam, nickel foam, stainless steel mesh, nickel mesh, and copper mesh. The current collector provided by the invention has a thickness of 1-12 μm, preferably 1-6 μm. The preferred conditions are used to better achieve higher current densities.
In the present invention, the positive electrode has a wide selection range, preferably, the positive electrode is selected from LiFe x1 Mn y1 M z1 PO 4 、Li 3 V 2 (PO 4 ) 3 、Li 3 V 3 (PO 4 ) 3 、LiNi 0.5-x2 Mn 1.5-y2 D x2+y2 O 4 、LiVPO 4 F、Li 1+x3 L 1－y3－ z3 E y3 Q z3 O 2 、Li 2 CuO 2 And Li (lithium) 5 FeO 4 At least one of (a) and (b); wherein, liFe x1 Mn y1 M z1 PO 4 (0.ltoreq.x1.ltoreq.1, 0.ltoreq.y1.ltoreq.1, 0.ltoreq.z1.ltoreq.1, x1+y1+z1=1, wherein M is at least one kind selected from Al, mg, ga, ti, cr, cu, zn and Mo), liNi 0.5- x2 Mn 1.5-y2 D x2+y2 O 4 (-0.1.ltoreq.x2.ltoreq.0.5, 0.ltoreq.y2.ltoreq.1.5, D is at least one selected from Li, co, fe, al, mg, ca, ti, mo, cr, cu, zn), li 1+x3 L 1－y3－z3 E y3 Q z3 O 2 (L, E, Q each independently selected from at least one of Li, co, mn, ni, fe, al, mg, ga, ti, cr, cu, zn, mo, F, I, S and B, -0.1.ltoreq.x3.ltoreq.0.2, 0.ltoreq.y3.ltoreq.1, 0.ltoreq.z3.ltoreq.1, 0.ltoreq.y3+z3.ltoreq.1).
Further preferably, the positive electrode is selected from LiAl 0.05 Co 0.15 Ni 0.80 O 2 、LiNi 0.80 Co 0.10 Mn 0.10 O 2 、LiNi 0.60 Co 0.20 Mn 0.20 O 2 、LiCoO 2 、LiMn 2 O 4 、LiFePO 4 、LiMnPO 4 、LiNiPO 4 、LiCoPO 4 、LiNi 0.5 Mn 1.5 O 4 And Li (lithium) 3 V 3 (PO 4 ) 3 At least one of them.
In the invention, the source of the positive electrode has a wide selection range, and can be obtained commercially or by self-making, and the invention is not limited to this.
The second aspect of the present invention provides a method for preparing a lithium ion battery, comprising the steps of:
(1)preparation of lithium alloy negative electrode：
A. Sequentially performing first sintering, first prepressing and first rolling on a first lithium source, a first non-metal source and a first magnesium source to obtain a first lithium alloy layer;
B. sequentially performing second sintering, second prepressing and second rolling on a second lithium source, a second non-metal source and a second magnesium source to obtain a second lithium alloy layer;
C. thirdly rolling the first lithium alloy layer and the second lithium alloy layer to obtain a lithium alloy anode;
(2)preparation of lithium ion batteries: assembling the lithium alloy cathode, the diaphragm, the anode and the electrolyte, wherein the first lithium alloy layer is close to the anode to obtain a lithium ion battery;
or assembling the lithium alloy negative electrode, the solid electrolyte and the positive electrode, wherein a first lithium alloy layer in the lithium alloy negative electrode is close to the positive electrode, so as to obtain a lithium ion battery;
wherein the nonmetallic elements in the first nonmetallic source and the second nonmetallic source are each independently selected from at least one of N, F and S;
wherein the mass ratio alpha of the nonmetallic element and the magnesium element in the first lithium alloy layer is larger than the mass ratio beta of the nonmetallic element and the magnesium element in the second lithium alloy layer.
In the present invention, the first lithium source and the second lithium source have a wide selection range as long as they contain lithium element. Preferably, the first lithium source and the second lithium source are each independently selected from at least one of lithium flakes, lithium magnesium alloy and lithium powder, preferably lithium flakes and/or lithium powder. The adoption of the preferable conditions is more beneficial to controlling the content of lithium in the lithium alloy cathode, reducing the introduction of impurities and avoiding other side reactions, thereby improving the electrochemical performance of the lithium ion battery.
In the present invention, the first magnesium source and the second magnesium source have a wide selection range as long as they contain magnesium element. Preferably, the first magnesium source and the second magnesium source are each independently selected from at least one of magnesium powder, lithium magnesium alloy and magnesium flakes, preferably magnesium powder and/or magnesium flakes. The preferable conditions are adopted, so that the lithium alloy anode with uniform magnesium element distribution is more favorable to be obtained, and the stability is high.
According to the present invention, preferably, the first nonmetallic source and the second nonmetallic source are each independently selected from a lithium-containing compound and/or a magnesium-containing compound containing the nonmetallic element; further preferably, the lithium-containing compound is selected from at least one of lithium nitride, lithium fluoride and lithium sulfide, preferably lithium nitride; the magnesium-containing compound is at least one selected from the group consisting of magnesium nitride, magnesium fluoride and magnesium sulfide, preferably magnesium nitride. The adoption of the preferable condition is more favorable for obtaining the lithium alloy cathode with high diffusion coefficient, the migration capability of lithium ions in the lithium alloy cathode is high, and the lithium alloy cathode can bear higher current density without dendrite generation.
In the present invention, the mass ratio of the first lithium source, the first non-metal source and the first magnesium source has a wide selection range, so long as the mass ratio of the lithium element, the magnesium element and the non-metal element in the first lithium alloy layer is 41.5 to 94.4:0.8-18:4.8-40.5, wherein the lithium element is selected from a first lithium source, an optional first non-metal source, and an optional first magnesium source, the magnesium element is selected from an optional first lithium source, an optional first non-metal source, and a first magnesium source, and the non-metal element is selected from a first non-metal source.
In a preferred embodiment, the first lithium source is a lithium sheet, the first non-metal source is lithium nitride, the first magnesium source is magnesium powder, and the mass ratio of the first lithium source to the first non-metal source to the first magnesium source is as follows: in the first lithium alloy layer, the mass ratio of the lithium element, the magnesium element and the nonmetallic element is 41.5-94.4:0.8-18:4.8-40.5, wherein the lithium element is selected from a first lithium source and a first non-metal source, the magnesium element is selected from a first magnesium source, and the non-metal element is selected from a first non-metal source.
In the present invention, the mass ratio of the second lithium source, the second non-metal source, and the second magnesium source has a wide selection range, so long as the mass ratio of the lithium element, the magnesium element, and the non-metal element in the second lithium alloy layer is 80.5 to 99.3:0.6-13.5:0.1-6, wherein the lithium element is selected from a second lithium source, an optional second non-metal source, and an optional second magnesium source, the magnesium element is selected from an optional second lithium source, an optional second non-metal source, and a second magnesium source, and the non-metal element is selected from a second non-metal source.
In a preferred embodiment, the second lithium source is a lithium sheet, the second non-metal source is magnesium nitride, the second magnesium source is magnesium powder, and the mass ratio of the second lithium source to the second non-metal source to the second magnesium source is as follows: in the second lithium alloy layer, the mass ratio of the lithium element to the magnesium element to the nonmetallic element is 80.5-99.3:0.6-13.5:0.1-6, wherein the lithium element is selected from a second lithium source, the magnesium element is selected from a second non-metal source and a second magnesium source, and the non-metal element is selected from a second non-metal source.
Preferably, the conditions of the first sintering include: the temperature is 300-1100 ℃, preferably 450-1000 ℃; the time is 0.5-10h, preferably 0.5-6h.
Preferably, the conditions of the second sintering include: the temperature is 400-900 ℃, preferably 450-700 ℃; the time is 0.5-10h, preferably 0.5-6h.
According to the present invention, it is preferable that the first sintering and the second sintering are each independently performed in an inert atmosphere provided by an inert gas, and further preferable that the inert gas is selected from at least one of helium, neon, argon, and krypton, and more preferably argon. The adoption of the preferable condition of the invention is more beneficial to reducing the cost and obtaining better economy.
In a preferred embodiment of the invention, a certain mass ratio of lithium sheet, lithium nitride and magnesium powder is subjected to first sintering in a crucible under an argon atmosphere, wherein the conditions of the first sintering comprise: the temperature is 300-1100 ℃ and the time is 0.5-10h, and the first lithium alloy block is obtained.
In a preferred embodiment of the invention, the lithium sheet, the magnesium nitride and the magnesium powder with certain mass ratio are subjected to second sintering in a crucible under the argon atmosphere, wherein the second sintering conditions comprise: the temperature is 400-900 ℃ and the time is 0.5-10h, and the second lithium alloy block is obtained.
In the present invention, the modes of the first pre-pressing and the second pre-pressing have a wide selection range, as long as the first lithium alloy block and the second lithium alloy block are each independently converted into a first lithium alloy sheet and a second lithium alloy sheet. Preferably, the first pre-compression and the second pre-compression are each independently performed in a tablet press.
In a preferred embodiment of the present invention, the first lithium alloy block is subjected to a first pre-pressing in a tablet press to obtain a first lithium alloy sheet having a thickness of 1-2 mm.
In a preferred embodiment of the invention, the second lithium alloy block is subjected to a second pre-pressing in a tablet press to obtain a second lithium alloy sheet with a thickness of 1-2 mm.
In the present invention, the conditions of the first preload and the second preload have a wide selection range, and preferably, the conditions of the first preload and the second preload each independently include: the dew point is less than-30 ℃, preferably from-60 ℃ to-40 ℃; the time is 5-60min, preferably 5-10min. The alloy cathode with no oxide layer or extremely low oxide layer on the surface is more favorable to be obtained by adopting the preferable conditions, and the alloy cathode has high stability.
In the present invention, the modes of the first rolling, the second rolling, and the third rolling have a wide selection range, so long as the first lithium alloy sheet, the second lithium alloy sheet, and the first lithium alloy layer and the second lithium alloy layer are each independently converted into a first lithium alloy layer, a second lithium alloy layer, and a lithium alloy anode. Preferably, the first rolling, the second rolling and the third rolling are each independently performed in a twin-roll machine.
In a preferred embodiment of the invention, the first lithium alloy sheet is clamped between PET (polyethylene terephthalate) release films and is transferred into a pair of rollers for first rolling, so that a first lithium alloy layer with the thickness of 0.5-10 mu m is obtained.
In a preferred embodiment of the invention, the second lithium alloy sheet is clamped between PET release films and is transferred into a pair of rollers for second rolling to obtain a second lithium alloy layer with the thickness of 1-40 mu m.
Preferably, the mass ratio of the first lithium alloy layer to the second lithium alloy layer is 1:0.1 to 80, preferably 1:1-40. The adoption of the preferable mass ratio is more beneficial to improving the high energy density and long-life cycle performance of the lithium ion battery.
In a preferred embodiment of the present invention, the first lithium alloy layer and the second lithium alloy layer are formed according to a ratio of 1: and (3) transferring the lithium alloy anode with the thickness of 1.5-50 mu m into a pair roller machine for third rolling by clamping the lithium alloy anode with the mass ratio of 0.1-80 in the middle of the PET release film.
In the present invention, the conditions of the first rolling, the second rolling, and the third rolling have a wide selection range, and preferably, the conditions of the first rolling, the second rolling, and the third rolling each independently include: the dew point is less than-30 ℃, preferably from-60 ℃ to-40 ℃; the time is 0.5-5min, preferably 1-1.5min. The adoption of the preferable conditions is more favorable for obtaining the alloy cathode without the surface oxide layer or with the extremely low oxide layer, and the alloy cathode has high stability.
According to the present invention, preferably, the method further comprises: and sequentially stacking the second lithium alloy layer and the first lithium alloy layer on the current collector, and then performing third rolling.
According to a preferred embodiment of the invention, the second lithium alloy layer and the first lithium alloy layer are sequentially stacked on the current collector, then the whole is clamped between PET release films and is transferred into a pair of rollers for third rolling, and the lithium alloy negative electrode (excluding the thickness of the current collector) with the thickness of 1.5-50 μm is obtained.
In the present invention, the positive electrode is defined as described above, and the present invention is not described herein.
In the present invention, the separator, the electrolyte and the solid electrolyte have a wide selection range, which are all conventional in the art, and the present invention is not described herein.
According to the present invention, preferably, the lithium ion battery is composed of the above-described lithium alloy anode, cathode, separator and electrolyte. The lithium alloy cathode has higher structural stability and safety performance, so that the cycle performance and the service life of the lithium ion battery are effectively improved.
In another preferred embodiment of the present invention, the lithium ion battery is assembled from the lithium alloy negative electrode, the solid electrolyte and the positive electrode.
The present invention will be described in detail by examples.
The parameters of the lithium alloy cathodes obtained in examples 1-7 and comparative examples 1-2 are all shown in Table 1.
Example 1
(1)First lithium alloy layer A1: performing first sintering on 2.4g of lithium sheets, 2g of lithium nitride powder and 0.1g of magnesium powder in a crucible under an argon atmosphere to obtain a first lithium alloy block, wherein the first sintering conditions comprise: at 850 DEG CThe interval is 2h;
and carrying out first pre-pressing on the cooled first lithium alloy block in a pre-pressing machine to obtain a first lithium alloy sheet with the thickness of 1mm, wherein the conditions of the first pre-pressing comprise: the dew point is-45 ℃ and the time is 5min;
carrying out first rolling on the first lithium alloy sheet in a pair roller to obtain a first lithium alloy layer A1, wherein the first rolling conditions comprise: the dew point is-45 ℃ and the time is 2min;
(2)second lithium alloy layer B1: second sintering of 3.88g of lithium flakes, 0.28g of lithium nitride powder and 0.34g of magnesium powder in a crucible under argon atmosphere to obtain a second lithium alloy block, wherein the conditions of the first sintering include: the temperature is 550 ℃ and the time is 2 hours;
and carrying out second pre-pressing on the cooled second lithium alloy block in a pre-pressing machine to obtain a second lithium alloy sheet with the thickness of 1mm, wherein the conditions of the second pre-pressing comprise: the dew point is-45 ℃ and the time is 5min;
and carrying out second rolling on the second lithium alloy sheet in a pair roller to obtain a second lithium alloy layer B1, wherein the second rolling conditions comprise: the dew point is-45 ℃ and the time is 2min;
(3)lithium alloy anode S1: the second lithium alloy layer B1 and the first lithium alloy layer A1 were mixed in a ratio of 1: and (3) stacking the lithium alloy anode S1 on a copper mesh current collector in sequence according to the mass ratio, and then performing third rolling in a pair roller to obtain the lithium alloy anode S1, wherein the third rolling conditions comprise: the dew point was-45℃for 2min.
Example 2
(1)First lithium alloy layer A2: performing first sintering on 2.17g of lithium tablets, 2.23g of lithium nitride powder and 0.1g of magnesium powder in a crucible under an argon atmosphere to obtain a first lithium alloy block, wherein the first sintering conditions comprise: the temperature is 850 ℃ and the time is 2 hours;
and carrying out first pre-pressing on the cooled first lithium alloy block in a pre-pressing machine to obtain a first lithium alloy sheet with the thickness of 1mm, wherein the conditions of the first pre-pressing comprise: the dew point is-45 ℃ and the time is 5min;
carrying out first rolling on the first lithium alloy sheet in a pair roller to obtain a first lithium alloy layer A2, wherein the first rolling conditions comprise: the dew point is-45 ℃ and the time is 2min;
(2)second lithium alloy layer B2: second sintering of 3.78g of lithium flakes, 0.38g of lithium nitride and 0.34g of magnesium powder in a crucible under argon atmosphere to obtain a second lithium alloy block, wherein the conditions of the first sintering include: the temperature is 750 ℃ and the time is 3 hours;
and carrying out second pre-pressing on the cooled second lithium alloy block in a pre-pressing machine to obtain a second lithium alloy sheet with the thickness of 1mm, wherein the conditions of the second pre-pressing comprise: the dew point is-45 ℃ and the time is 5min;
and carrying out second rolling on the second lithium alloy sheet in a pair roller to obtain a second lithium alloy layer B2, wherein the second rolling conditions comprise: the dew point is-45 ℃ and the time is 2min;
(3)lithium alloy anode S2: second lithium alloy layer B2 and first lithium alloy layer A2 and a ratio of 4: and (3) stacking the lithium alloy anode S2 on a copper mesh current collector in sequence according to the mass ratio, and then performing third rolling in a pair roller to obtain the lithium alloy anode S2, wherein the third rolling conditions comprise: the dew point was-45℃for 2min.
Example 3
(1)First lithium alloy layer A3: first sintering 3.66g of lithium flakes, 0.74g of lithium nitride powder and 0.1g of magnesium powder in a crucible under an argon atmosphere to obtain a first lithium alloy block, wherein the first sintering conditions comprise: the temperature is 850 ℃ and the time is 2 hours;
and carrying out first pre-pressing on the cooled first lithium alloy block in a pre-pressing machine to obtain a first lithium alloy sheet with the thickness of 1mm, wherein the conditions of the first pre-pressing comprise: the dew point is-45 ℃ and the time is 5min;
carrying out first rolling on the first lithium alloy sheet in a pair roller to obtain a first lithium alloy layer A3, wherein the first rolling conditions comprise: the dew point is-45 ℃ and the time is 2min;
(2)second lithium alloy layer B3: second sintering 3.78g of lithium flakes, 0.38g of magnesium nitride and 0.34g of magnesium powder in a crucible under argon atmosphere to obtain a second lithium alloy blockThe conditions for the first sintering include: the temperature is 750 ℃ and the time is 3 hours;
and carrying out second pre-pressing on the cooled second lithium alloy block in a pre-pressing machine to obtain a second lithium alloy sheet with the thickness of 1mm, wherein the conditions of the second pre-pressing comprise: the dew point is-45 ℃ and the time is 5min;
and carrying out second rolling on the second lithium alloy sheet in a pair roller to obtain a second lithium alloy layer B3, wherein the second rolling conditions comprise: the dew point is-45 ℃ and the time is 2min;
(3)lithium alloy anode S3: the first lithium alloy layer A3 and the second lithium alloy layer B3 are mixed according to the ratio of 1: and (4) carrying out third rolling in a pair roller machine to obtain a lithium alloy anode S3, wherein the third rolling conditions comprise: the dew point is-45 ℃ and the time is 2min.
Example 4
The method of example 1 was followed, except that the mass ratio of the first lithium alloy layer A1 to the second lithium alloy layer B1 was replaced with 1:9, obtaining the lithium alloy anode S4.
Example 5
The procedure of example 1 was followed except that the first nonmetallic source was replaced with lithium fluoride, resulting in a lithium alloy negative electrode S5.
Example 6
The procedure of example 1 was followed except that the first nonmetallic source and the second nonmetallic source were replaced with lithium fluoride and magnesium fluoride, respectively, to obtain a lithium alloy negative electrode S6.
Example 7
The procedure of example 1 was followed except that the first nonmetallic source and the second nonmetallic source were replaced with lithium sulfide and magnesium sulfide, respectively, to obtain a lithium alloy negative electrode S7.
Comparative example 1
The procedure of example 1 was followed except that steps (2) and (3) were omitted to obtain a lithium alloy negative electrode D1.
Comparative example 2
The procedure of example 1 was followed, except that steps (1) and (3) were omitted, to obtain lithium alloy D2.
TABLE 1
Figure BDA0002555203340000161
Table 1, below
Figure BDA0002555203340000162
Note that: y is a nonmetallic element, and Y is at least one selected from N, F and S; the thickness of the lithium alloy negative electrode does not include the thickness of the current collector.
The lithium alloy cathodes S1 to S7 and D1 to D2 prepared in examples 1 to 7 and comparative examples 1 to 2 were subjected to an electrical property test.
Test example 1
Preparation and testing of Li vs Li symmetric cells: two lithium alloy cathodes (S1-S7 and D1-D2) were placed on either side of a separator (Celgard 2400), 4mol/L LiCF 3 SO 3 And (3) using the solvent DME as electrolyte, and assembling the laminated battery to obtain the Li vs Li symmetrical batteries PS1-7 and PD1-2.
Test conditions: (1) At 25℃1mA/cm 2 1h charge/1 h discharge, and performing a symmetrical battery test to evaluate the stability of the Li vs Li symmetrical batteries PS1-7 and PD1-2, wherein the test results are shown in Table 2;
(2) At 25℃at 0.1mA/cm, respectively 2 、0.5mA/cm 2 、1mA/cm 2 、1.5mA/cm 2 、2mA/cm 2 、3mA/cm 2 Carrying out a lithium deposition experiment under the current density of 2 hours, observing the deposition morphology of lithium, and testing the deposition morphology of the Li vs Li symmetrical batteries PS1-7 and PD1-2, wherein the test results are shown in Table 3;
wherein the Li vs Li symmetric battery PS1 is 1.5mA/cm 2 And 2mA/cm 2 SEM images of 2h deposited lithium at current densities of (a) are shown in fig. 1 and 2, respectively.
TABLE 2
Li vs Li symmetrical battery Cycle number/times
Example 1 PS-1 1100 times without short circuit
Example 2 PS-2 1250 times without short circuit
Example 3 PS-3 1300 times, without short circuit
Example 4 PS-4 1800 times without short circuit
Example 5 PS-5 1020 times without short circuit
Example 6 PS-6 1018 times, no short circuit
Example 7 PS-7 1000 times without short circuit
Comparative example 1 PD-1 800 times, no short circuit
Comparative example 2 PD-2 500 times short circuit
As can be seen from the data in Table 2, the symmetrical cells PS1-7 prepared in examples 1-7 had a uniform and high cycle number and no short circuit, PD-1 had a high nitrogen/magnesium ratio, which was advantageous for uniform deposition of lithium and thus no short circuit, but had a reduced cycle number because of limited delithiability in the alloy with a high nitrogen/magnesium ratio and no effective replenishment of cycle loss, and PD-2 had a short circuit. The lithium alloy negative electrode provided by the invention has higher cycle stability and safety performance.
TABLE 3 Table 3
Figure BDA0002555203340000181
Note that: thickness refers to the deposition thickness.
Table 3 shows the sequence
Figure BDA0002555203340000182
/>
Figure BDA0002555203340000191
Note that: thickness refers to the deposition thickness.
As can be seen from the data in Table 3, the symmetrical cells PS1-7 and PD1 prepared in examples 1-7 and comparative example 1 were measured at 0.1-3mA/cm 2 No lithium dendrite formation was observed in the current density range of (3), and examples 1 to 4 and comparative example 1 were conducted at a current density of less than 1mA/cm 2 Can realize the deposition of metallic lithium inside the alloy system under the current density,the PD-2 surface has lithium dendrite formation, and the concentration is 0.1mA/cm 2 、0.5mA/cm 2 、1mA/cm 2 、1.5mA/cm 2 、2mA/cm 2 、3mA/cm 2 Lithium deposition was performed for 2 hours at a current density of 1 μm, 5 μm, 10 μm, 15 μm, 20 μm, and 30 μm, respectively, and it was found that the deposition thicknesses in examples 1 to 7 and comparative examples 1 to 2 were compared, and that the more dense lithium deposition was obtained in each of examples 1 to 7, whereas the volume deformation was smaller at a small current density and a low deposition amount in comparative example 1, and the volume deformation was larger in comparative example 2. In conclusion, according to analysis, the lithium alloy negative electrode provided by the invention has better structural stability and safety performance, and no dendrite is generated.
Test example 2
Preparation of a metal lithium negative electrode battery:
(1) Uniformly mixing 4.9mg of positive electrode active material (lithium cobaltate), 0.05mg of conductive agent (acetylene black) and 0.05mg of binder (PVDF) in NMP (N-methylpyrrolidone) by using a vacuum stirrer to form stable uniform slurry, wherein the stirring speed is 1000rpm, and the time is 12 hours; then coating the obtained slurry on the two sides of a current collector aluminum sheet, drying at 80 ℃, and cutting into positive plates with the size of 21 multiplied by 42 mm; and then drying at 80 ℃, and tabletting by a roll squeezer to obtain the positive plate Z.
(2) The positive plate Z, the diaphragm and the lithium alloy negative electrode (S1-S7 and D1-D2) are stacked layer by layer to assemble a laminated battery, a first lithium alloy layer in the lithium alloy negative electrode is close to the positive plate, and 0.4g of electrolyte (4 mol/L LiCF) is added dropwise 3 SO 3 The solvent is DME), and then packaging to obtain the metal lithium anode batteries QS1-7 and QD1-2.
The battery is subjected to charge and discharge cycle test at 0.4C under 298+ -1K conditions on a LAND CT 2001C secondary battery performance detection device by using metal lithium negative electrode batteries QS1-7 and QD1-2.
Specific test conditions: standing for 10min; constant voltage charging to 4.2V/0.05C cut-off; standing for 10min; constant current discharge to 3V is 1 cycle. When the battery capacity is lower than 80% of the first discharge capacity in the cycling process, the cycle times are defined as the cycle life of the battery, each group is averaged, the parameter, the data of the average first discharge capacity of the battery and the thickness change rate of the battery before and after cycling are set, the test is stopped when the cycle times reach 500, and the test results are shown in table 4.
TABLE 4 Table 4
Figure BDA0002555203340000201
As can be seen from the data in table 4, compared with comparative examples 1-2, the cycle performance and the volume change of the batteries prepared in examples 1-7 are improved, the cycle performance of the battery can be further improved by properly increasing the proportion of the second lithium alloy layer, the content of lithium in the lithium alloy negative electrode can be increased by increasing the second lithium alloy layer, and meanwhile, smaller volume deformation is obtained, the volume deformation caused by the migration of lithium ions into the second lithium alloy layer through the first lithium alloy layer can be greatly restrained by relatively higher magnesium content in the second lithium alloy layer, and the structural stability of the lithium alloy negative electrode is effectively improved; in addition, after 200 cycles, the lithium metal negative electrode batteries prepared in examples 1 to 7 all showed higher volumetric energy density. Therefore, the lithium ion battery provided by the invention has higher energy density and cycle performance.
Test example 4
The lithium alloy negative electrodes (S1 to S7 and D1 to D2) prepared in examples 1 to 7 and comparative examples 1 to 2 were observed for changes in the lithium alloy negative electrodes under an air atmosphere (humidity 10%) at 25 ℃ and evaluated for stability in the air atmosphere, and experimental results are shown in table 5.
TABLE 5
Lithium alloy negative electrode 0.5h 1h 2h 4h 8h 24h
Example 1 S1 No change No change No change Blackening Change ash Whitening of
Example 2 S2 No change No change No change No change Blackening Whitening of
Example 3 S3 No change Change ash Whitening of Whitening of Whitening of Whitening of
Example 4 S4 No change No change No change Blackening Change ash Whitening of
Example 5 S5 No change No change No change Blackening Change ash Whitening of
Example 6 S6 No change No change No change Blackening Change ash Whitening of
Example 7 S7 No change No change No change Blackening Change ash Whitening of
Comparative example 1 D1 No change No change No change Blackening Change ash Whitening of
Comparative example 2 D2 No change Change ash Whitening of Whitening of Whitening of Whitening of
As can be seen from the data in Table 5, the lithium alloy negative electrode provided by the invention maintains the original form within a certain time range, has certain tolerance to moisture, and improves the stability of the lithium alloy negative electrode under the air atmosphere.
The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, a number of simple variants of the technical solution of the invention are possible, including combinations of the individual technical features in any other suitable way, which simple variants and combinations should likewise be regarded as being disclosed by the invention, all falling within the scope of protection of the invention.

Claims (8)

1. The lithium ion battery is characterized by comprising a positive electrode and a lithium alloy negative electrode, wherein the lithium alloy negative electrode comprises a first lithium alloy layer and a second lithium alloy layer arranged on the surface of the first lithium alloy layer, and the first lithium alloy layer is close to the positive electrode;
the first lithium alloy layer and the second lithium alloy layer each contain a lithium element, a magnesium element and a nonmetallic element, wherein the nonmetallic element is at least one selected from N, F and S;
wherein the mass ratio alpha of the nonmetallic element and the magnesium element in the first lithium alloy layer is larger than the mass ratio beta of the nonmetallic element and the magnesium element in the second lithium alloy layer;
wherein, in the first lithium alloy layer, the mass ratio alpha of the nonmetallic element and the magnesium element is 1.5-9:1, a step of; in the second lithium alloy layer, the mass ratio beta of the nonmetallic element to the magnesium element is 1:1.5-9;
wherein, based on the weight of the first lithium alloy layer, the mass content of magnesium element in the first lithium alloy layer is 0.8-18%, and the mass content of non-metal element is 4.8-40.5%; the mass content of the magnesium element in the second lithium alloy layer is 0.6-13.5% and the mass content of the nonmetallic element is 0.1-6% based on the total amount of the second lithium alloy layer.
2. The lithium ion battery of claim 1, wherein the mass ratio of the first lithium alloy layer to the second lithium alloy layer is 1:0.1-80; and/or the number of the groups of groups,
the nonmetallic elements in the first lithium alloy layer and the second lithium alloy layer are the same or different.
3. Lithium ion battery according to claim 1 or 2, characterized in that the thickness of the negative electrode is 1.5-50 μm, the thickness of the first lithium alloy layer is 0.5-10 μm, and the thickness of the second lithium alloy layer is 1-40 μm.
4. The lithium ion battery of claim 1 or 2, wherein the lithium alloy negative electrode further comprises: and the surface of the current collector is sequentially provided with a second lithium alloy layer and a first lithium alloy layer.
5. The preparation method of the lithium ion battery is characterized by comprising the following steps of:
（1）preparation of lithium alloy negative electrode：
A. Sequentially performing first sintering, first prepressing and first rolling on a first lithium source, a first non-metal source and a first magnesium source to obtain a first lithium alloy layer;
B. sequentially performing second sintering, second prepressing and second rolling on a second lithium source, a second non-metal source and a second magnesium source to obtain a second lithium alloy layer;
C. thirdly rolling the first lithium alloy layer and the second lithium alloy layer to obtain a lithium alloy anode;
（2）preparation of lithium ion batteries: assembling the lithium alloy negative electrode, the diaphragm, the positive electrode and the electrolyte, wherein a first lithium alloy layer in the lithium alloy negative electrode is close to the positive electrode, so as to obtain a lithium ion battery;
or assembling the lithium alloy negative electrode, the solid electrolyte and the positive electrode, wherein a first lithium alloy layer in the lithium alloy negative electrode is close to the positive electrode, so as to obtain a lithium ion battery;
wherein the nonmetallic elements in the first nonmetallic source and the second nonmetallic source are each independently selected from at least one of N, F and S;
wherein the mass ratio alpha of the nonmetallic element and the magnesium element in the first lithium alloy layer is larger than the mass ratio beta of the nonmetallic element and the magnesium element in the second lithium alloy layer;
wherein, in the first lithium alloy layer, the mass ratio alpha of the nonmetallic element and the magnesium element is 1.5-9:1, a step of; in the second lithium alloy layer, the mass ratio beta of the nonmetallic element to the magnesium element is 1:1.5-9;
wherein, based on the weight of the first lithium alloy layer, the mass content of magnesium element in the first lithium alloy layer is 0.8-18%, and the mass content of non-metal element is 4.8-40.5%; the mass content of the magnesium element in the second lithium alloy layer is 0.6-13.5% and the mass content of the nonmetallic element is 0.1-6% based on the total amount of the second lithium alloy layer.
6. The method of claim 5, wherein the first and second non-metal sources are each independently selected from a lithium-containing compound and/or a magnesium-containing compound comprising the non-metal element; and/or the number of the groups of groups,
the lithium-containing compound is selected from at least one of lithium nitride, lithium fluoride and lithium sulfide;
the magnesium-containing compound is at least one selected from the group consisting of magnesium nitride, magnesium fluoride and magnesium sulfide.
7. The method according to claim 5 or 6, wherein the mass ratio of the lithium element, the magnesium element and the nonmetallic element in the first lithium alloy layer is 41.5 to 94.4:0.8-18:4.8-40.5; and/or the number of the groups of groups,
in the second lithium alloy layer, the mass ratio of the lithium element to the magnesium element to the nonmetallic element is 80.5-99.3:0.6-13.5:0.1-6.
8. The method according to claim 5 or 6, characterized in that the method further comprises: and sequentially stacking the second lithium alloy layer and the first lithium alloy layer on the current collector, and then performing third rolling.
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