CN108899472B - Electrode plate for lithium metal battery, preparation method of electrode plate and lithium metal battery - Google Patents

Electrode plate for lithium metal battery, preparation method of electrode plate and lithium metal battery Download PDF

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CN108899472B
CN108899472B CN201810813168.2A CN201810813168A CN108899472B CN 108899472 B CN108899472 B CN 108899472B CN 201810813168 A CN201810813168 A CN 201810813168A CN 108899472 B CN108899472 B CN 108899472B
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sponge
lithium
battery
lithium metal
metal battery
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CN108899472A (en
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朱彦武
余晗
王欣媛
谢兼
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University of Science and Technology of China USTC
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • 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
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • 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

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Abstract

The invention provides a negative pole piece for a lithium metal battery, which is formed by pressing a metal lithium piece and sponge. When the negative pole piece provided by the invention is applied to the lithium metal battery, the structure of the traditional lithium metal battery can be simplified, the sponge elastic interface layer is introduced to replace a diaphragm to play an electron blocking role, and the introduction of the elastic interface material can relieve the volume change and the interface instability inside the battery in the battery circulation. And the sponge medium layer has very good wettability with electrolyte, and has stronger thermal deformation resistance compared with a common Polypropylene diaphragm (Polypropylene). Meanwhile, the elastic three-dimensional framework structure of the sponge is beneficial to inhibiting the growth of dendritic crystals in the circulation process of the lithium metal battery; and is also beneficial to relieving the volume change of the cathode. Therefore, the lithium metal battery can be further developed from another angle by the aid of the composite metal lithium negative electrode without the diaphragm structure designed by using the sponge material.

Description

Electrode plate for lithium metal battery, preparation method of electrode plate and lithium metal battery
Technical Field
The invention belongs to the technical field of lithium metal batteries, and particularly relates to an electrode plate for a lithium metal battery, a preparation method of the electrode plate and the lithium metal battery.
Background
On the one hand, the high-capacity lithium ion battery has the highest theoretical capacity (3860mA h g)-1) Lowest electrochemical potential (-3.04V), lower density (0.534g cm)-3) And the like, the metallic lithium negative electrode is considered to be a possible development direction of a next generation energy storage system. On the other hand, with the development of next-generation high-energy battery systems, for example: the research and development of lithium air batteries and lithium sulfur batteries and the application research of lithium metal batteries also show the importance of the lithium air batteries and the lithium sulfur batteries. However, since the problems of high activity and lithium dendrite of lithium metal itself are not solved, its safety and cyclability limit commercial applications. Wherein: (1) from the perspective of safety, lithium dendrites growing under continuous circulation easily pierce through a battery diaphragm, so that the anode and the cathode of the battery are short-circuited, and accident potential hazards such as fire are generated. (2) From the structural consideration of the full battery, the lithium metal of the negative electrode brings no host volume change with the charge and discharge degree, and the following calculation results show that: in theory, whenThe circulating surface capacity of the battery reaches 10mAh/cm2At this time, the interfacial movement of lithium in the full cell will reach 50 μm, which in turn generates a large internal stress. (3) Considering from the interface of the negative electrode, firstly, dendrite protrusions initially generated at the interface of the negative electrode and the electrolyte cause uneven distribution of local charges, and the growth of lithium dendrite is accelerated; secondly, the generation of negative lithium dendrites causes the surface of lithium metal to continuously regenerate a Solid Electrolyte Interface (SEI) film during cycling, which affects the coulombic efficiency of the battery.
On the other hand, in the conventional lithium ion battery at present, the separator is the material with the highest technical barrier and capillary index among the four main materials of the battery. Generally, the separator in the battery module is made of a porous polymer film, a glass fiber film, or a porous ceramic film, and functions to block electrons and allow ions to pass therethrough. Such as: chinese patent publication No. CN106252568 discloses a high temperature resistant lithium ion battery separator and a preparation method thereof, and for a novel lithium metal battery, the research on the separator is relatively few, and many Polypropylene films (Polypropylene), Glass Fiber films (Glass Fiber) and Polypropylene-Polyethylene-Polypropylene composite films (Polypropylene-Polyethylene-Polypropylene) still used in the conventional lithium ion battery are adopted. However, the diaphragm has poor heat deformation resistance, so that the probability of contact between the positive electrode and the negative electrode of the lithium battery is increased.
Disclosure of Invention
In view of the above, the present invention provides a negative electrode plate for a lithium metal battery, and when the negative electrode plate for a lithium metal battery provided by the present invention is applied to a lithium metal battery, a diaphragm structure can be omitted, and an elastic interface formed by sponge in the negative electrode plate can alleviate volume change and interface instability in the battery during battery cycle.
The invention provides a negative pole piece for a lithium metal battery, which is characterized by being formed by pressing a metal lithium piece and sponge.
Preferably, the thickness of the metal lithium sheet is 50-1000 μm, the thickness of the sponge is 1-5 mm, and the thickness of the negative electrode sheet is 800-6000 μm.
Preferably, the sponge has a density of about 0.01 to 0.02g/cm3The porosity reaches 98-99%, and the pore diameter is 50-100 μm.
Preferably, the sponge is selected from one or more of polyurethane sponge, rubber sponge, and melamine sponge.
The invention also provides a preparation method of the negative pole piece for the lithium metal battery, which comprises the following steps:
and (3) under the condition of protective atmosphere, applying physical pressure to compound the sponge and the lithium sheet to obtain the negative pole piece.
Preferably, the protective atmosphere conditions are selected from argon atmosphere, and the water oxygen content in the protective atmosphere is less than 0.1 ppm.
The invention also provides a lithium metal battery, which comprises a positive electrode, a negative electrode and electrolyte, and does not comprise a diaphragm, wherein the negative electrode is selected from the negative electrode pole piece.
Preferably, the electrolyte is selected from a lithium ion battery electrolyte or a lithium sulfur battery electrolyte.
Preferably, the positive electrode material of the positive electrode is selected from sulfur and conventional intercalation-type positive electrode materials: li4Ti5O12、LiFePO4、LiCoO2One or more of them.
Compared with the prior art, the invention provides a negative pole piece for a lithium metal battery, which is formed by pressing a metal lithium piece and sponge. When the negative pole piece provided by the invention is applied to the lithium metal battery, the structure of the traditional lithium metal battery can be simplified, the sponge elastic interface layer is introduced to replace a diaphragm to play an electron blocking role, and the introduction of the elastic interface material can relieve the volume change and the interface instability inside the battery in the battery circulation. And the sponge medium layer has very good wettability with electrolyte, and has stronger thermal deformation resistance compared with a common Polypropylene diaphragm (Polypropylene). Meanwhile, the elastic three-dimensional framework structure of the sponge is beneficial to inhibiting the growth of dendritic crystals in the circulation process of the lithium metal battery; and is also beneficial to relieving the volume change of the cathode. Therefore, the lithium metal battery can be further developed from another angle by the aid of the composite metal lithium negative electrode without the diaphragm structure designed by using the sponge material.
The result shows that the coulombic efficiency of the half-cell assembled by the negative pole piece for the lithium metal battery can reach 98% after 63 circles according to the conventional method. The cycle performance of the lithium metal symmetrical battery with the sponge composite material without the diaphragm structure is tested to obtain: at a high current density (10mA cm)-2) And large capacity (10 mAhcm)-2) Lower overpotential is also shown and the cycle is stable for 200 hours; at 1mA cm-2Lower current density and 1mAhcm-2Also exhibits lower overpotential at capacity and can stabilize cycling.
Drawings
FIG. 1 is an optical micrograph (left) and an SEM image (right) of a sponge material selected in examples 1 and 2 of the present invention;
FIG. 2 is a digital photograph comparing the sponge material selected in examples 1 and 2 of the present invention with a polypropylene diaphragm maintained at 150 ℃ for 1 hour;
FIG. 3 is a SEM front view, a cross-sectional view and a partial view of a composite of sponge and lithium metal in examples 1 and 2 of the present invention;
FIG. 4 is a comparison graph of cycle test of a symmetrical battery with no separator structure design of sponge and metal lithium composite electrode prepared in example 1 and comparative example 1 of the present invention and cycle test of a lithium metal symmetrical battery;
FIG. 5 is a schematic structural diagram of a lithium metal battery (model: CR2032) with no-diaphragm structure design of sponge and lithium metal composite electrode assembled by testing coulombic efficiency in example 2 of the present invention;
fig. 6 is a coulomb efficiency test comparison graph of lithium metal half-cells with no diaphragm structure design of sponge and metal lithium composite electrodes prepared in example 2 and comparative example 2 of the present invention;
FIG. 7 is a comparison graph of cycling and coulombic efficiency tests for half cells assembled with sponge elastic interface layers of different thicknesses as described in example 3 of the present invention;
fig. 8 is a graph of the first three cycles of cycling and coulombic efficiency testing of the full cell assembled with the sponge elastic interface layer described in example 4 of the present invention.
Detailed Description
The invention provides a negative pole piece for a lithium metal battery, which is formed by pressing a metal lithium piece and sponge.
Wherein the thickness of the metal lithium sheet is 50-1000 μm, preferably 200-800 μm, more preferably 300-600 μm, more preferably 0.4-0.5 mm, and most preferably 0.46 mm.
The diameter of the lithium metal sheet is preferably 12-16 mm, and more preferably 14 mm.
In the invention, the lithium metal sheet is preferably a conventional round lithium sheet for preparing a lithium ion battery half-cell cathode material in the field. The lithium metal sheet may have other shapes, and is not particularly limited.
The thickness of the sponge is 1-5 mm, preferably 2-4 mm, and more preferably 2.5-3 mm.
The thickness of the formed negative pole piece is 800-6000 μm, and preferably 1500-2900 μm. When the electrode plate is circular, the diameter of the electrode plate is preferably 5-16 mm, and more preferably 10 mm.
In the invention, the density of the sponge is about 0.01-0.02 g/cm3The porosity reaches 98-99%, and the pore diameter is 50-100 μm, preferably 60-90 μm, and more preferably 70-80 μm.
The sponge is selected from one or more of polyurethane sponge, rubber sponge and melamine sponge.
In the invention, the negative pole piece for the lithium metal battery is formed by pressing a metal lithium piece and sponge. Wherein, because the lithium metal texture is soft, with the two suppression processes, the lithium of the one side that contacts with the sponge produces deformation because of the pressure and can imbed in the hole of sponge, consequently can produce the composite construction of lithium layer-lithium/sponge transition layer-sponge layer. The lithium/sponge transition layer is a transition layer structure formed by lithium inserted into pores of the sponge when the metal lithium sheet and the sponge are pressed.
The invention also provides a preparation method of the negative pole piece for the lithium metal battery, which comprises the following steps:
and (3) under the condition of protective atmosphere, applying physical pressure to compound the sponge and the lithium sheet to obtain the negative pole piece.
Firstly, cutting a sponge to a required thickness, and then cutting the sponge to obtain a sponge sheet with a certain size;
then overlapping the sponge sheet and the lithium sheet, and applying physical pressure under the condition of protective atmosphere to obtain a composite sheet;
wherein the protective atmosphere condition is selected from argon atmosphere, and the water oxygen content in the protective atmosphere is less than 0.1 ppm. In the present invention, the pressing process of the sponge sheet and the lithium sheet is preferably performed in a glove box. The present invention preferably applies physical pressure using a hydraulic packaging machine.
And finally, cutting the obtained composite sheet to obtain the negative pole piece with the required size.
The shape and size of the negative pole piece are not particularly limited, and the shape and size of the negative pole piece which can be used for the lithium metal battery and is known by the technical personnel in the field can be only needed.
The structural design makes full use of the three-dimensional structure of the sponge material and the elasticity capable of accommodating volume changes on the one hand, and also makes use of the physical barrier of the sponge layer on the other hand, thereby playing the roles of blocking electrons and conducting ions similar to the currently used diaphragm. The whole preparation process is simple and can be produced in large scale.
The lithium metal half-cell and the symmetrical cell assembled by the negative pole piece show more stable coulombic efficiency and more excellent cycle performance than lithium metal under different current densities. The coulombic efficiency of the half-cell assembled by the negative pole piece can reach 98% after 63 circles according to a conventional method, and the test result is obviously superior to that of a comparative cell assembled by a metal lithium piece and a Polypropylene diaphragm (Polypropylene) under the same condition. The cycle performance of the lithium metal symmetrical battery without the diaphragm structure obtained by the negative pole piece provided by the invention is tested to obtain: at a high current density (10mA cm)-2) And large capacity (10 mAhcm)-2) Lower overpotential is also shown and the cycle is stable for 200 hours; at 1mA cm-2Lower current density and 1mAhcm-2Also exhibits lower overpotential at capacity and mayAnd (5) stabilizing and circulating.
Wherein, half battery structure includes by negative pole shell to positive pole shell in proper order: the lithium battery comprises a negative electrode shell, a lithium sheet-sponge, electrolyte, a copper sheet, a gasket, an elastic sheet and a positive electrode shell.
The symmetrical battery structure comprises a negative electrode shell and a positive electrode shell in sequence: a negative electrode case; lithium sheet-sponge-lithium sheet; gasket, shell fragment and positive pole shell.
The invention also provides a lithium metal battery, which comprises a positive electrode, a negative electrode and electrolyte, and does not comprise a diaphragm, wherein the negative electrode is selected from the negative electrode pole piece for the lithium metal battery.
The electrolyte of the present invention is not particularly limited, and may be a lithium ion battery electrolyte or a lithium sulfur battery electrolyte, which is well known to those skilled in the art. Preferably, the lithium sulfur battery electrolyte may be selected from 1M LiTFSI (DOL: DME ═ 1:1 vol%) +2 wt% LiNO3The electrolyte is formed by the formation of the electrolyte,
the method specifically comprises the following steps: DOL and DME in a volume ratio of 1:1 are used as a mixed solvent, the concentration of LiTFSI in the mixed solvent is 1M, and 2 wt% LiNO is added into the mixed solvent3The electrolyte is formed.
The lithium ion electrolyte may be selected from 1M LiF6(EC: DEC ═ 1:1 vol%), specifically, using EC and DEC in a volume ratio of 1:1 as a mixed solvent, LiF6The concentration therein was 1M.
The present invention does not specifically limit the positive electrode of the lithium metal battery, and any kind of positive electrode material known to those skilled in the art may be used.
In the present invention, the positive electrode material is selected from sulfur and conventional intercalation-type positive electrodes: li4Ti5O12、LiFePO4、LiCoO2One or more of them. .
The assembly process of the cell is preferably carried out in a glove box with inert atmosphere conditions. And then, obtaining the lithium metal symmetrical battery with the button type diaphragm-free structure and the half battery for testing the coulombic efficiency by adopting a conventional battery packaging method in the field.
Referring to fig. 5, the structure of the half cell includes: and sequentially assembling the negative electrode shell, the lithium sheet, the sponge, the electrolyte, the lithium sheet/copper foil, the gasket, the elastic sheet and the positive electrode shell.
In some embodiments of the present invention, the structure of the lithium metal full cell includes: the lithium metal full cell separator-free structure using LTO can be designed as follows: the cathode comprises a cathode shell, the cathode pole piece, electrolyte, LTO, a gasket, an elastic sheet and an anode shell.
The preparation method of the negative pole piece provided by the invention is simple in process and low in cost, and the obtained lithium metal battery without the diaphragm structure is good in performance.
The invention provides a novel lithium metal battery without a diaphragm structure, and the sponge and lithium metal symmetrical battery without the diaphragm structure prepared by pressure compounding can keep the long-time circulation stability under the set different current densities.
The invention also provides a large current density cycle test result of the lithium metal half battery and the symmetric battery assembled by the sponge and the lithium metal diaphragm-free structure, and compared with a pure lithium metal symmetric battery, the novel diaphragm-free system shows more excellent cycle stability.
The symmetrical battery testing method comprises the following steps: after the assembled button cell is kept still for 12 hours, the button cell is discharged for 1 hour at a set current density, then is charged for 1 hour at the same current density, and the discharging and charging processes are continuously repeated until the overpotential of the cell is sharply increased or sharply reduced, and the experiment is stopped, so that the open circuit or short circuit of the cell is indicated. The test method can be used for researching the cycle stability of the lithium deposition and precipitation process of the adopted sponge and metal lithium composite material under the set current density and the effect of the sponge and metal lithium composite material on inhibiting the metal lithium dendrite.
The method for testing the coulombic efficiency of the half-cell comprises the following steps: and (3) after the assembled lithium metal button battery is kept still for 12 hours, discharging for 1 hour at a set current density, then charging to 1V cut-off at the same current density, calculating the proportion of the charging capacity to the discharging capacity in the charging and discharging circulation process, and evaluating the capacity fading speed of a battery system and the reversibility of battery circulation through the proportion value.
The invention fully utilizes the elastic three-dimensional skeleton structure of the sponge, simultaneously relieves the instability and the volume change of the battery interior by the elastic sponge interface layer, simultaneously plays the physical barrier effect of the sponge, and can replace the Polypropylene diaphragm (Polypropylene) or Glass Fiber diaphragm (Glass Fiber) which is commonly used in the prior lithium metal battery to form a novel diaphragm-free negative electrode structure. The whole preparation process is simple and feasible, and the novel lithium metal battery without the diaphragm structure saves cost and is beneficial to large-scale application and development.
In order to further understand the present invention, the electrode plate for a lithium metal battery, the preparation method thereof, and the lithium metal battery provided by the present invention are described below with reference to the following examples, and the protection scope of the present invention is not limited by the following examples.
Example 1
The preparation and the cycle test of the lithium metal battery with the melamine sponge and the metal lithium composite elastic interface material without the diaphragm structure design:
cutting the prepared clean sponge material into 2.5mm thick by using a scalpel; cutting a sponge wafer with the diameter of 16mm by using a punch; wherein the density of the sponge is 0.01-0.02 g/cm3The porosity is 98-99%, and the pore diameter is 50-100 μm. Referring to fig. 1, fig. 1 is an optical microscope (left) and SEM image (right) of the sponge material selected for use in examples 1 and 2 of the present invention.
The sponge material was kept at 150 ℃ for 1 hour, and the front and rear states and the size were photographed, and the result is shown in fig. 2, and fig. 2 is a digital photograph comparing the sponge material selected in examples 1 and 2 of the present invention with the polypropylene diaphragm kept at 150 ℃ for 1 hour. In fig. 2, the left image is a digital photograph of the sponge material and the polypropylene separator selected in examples 1 and 2 of the present invention before heat treatment, and the right image is a digital photograph of the sponge material and the polypropylene separator selected in examples 1 and 2 of the present invention after being kept at 150 ℃ for 1 hour. As can be seen from FIG. 2, the sponge materials selected in examples 1 and 2 did not change significantly in size after being held at 150 ℃ for 1 hour, but the polypropylene separator showed significantly less shrinkage in size.
A lithium metal sheet was prepared to have a thickness of 450. mu.m. And (3) superposing the sponge material and the metal lithium sheet, and applying physical pressure in an argon glove box by using a small hydraulic packaging machine to obtain the sponge-lithium sheet negative pole piece with the thickness of 800-1200 mu m.
The scanning electron microscope observation of the sponge-lithium sheet negative pole piece is shown in fig. 1, and fig. 1 is a SEM front view (upper), a cross-sectional view (middle) and a partial view (lower) of a composite part of the sponge and the lithium metal composite in examples 1 and 2 of the present invention. As can be seen from the partial view of the recombination site, lithium on the side in contact with the sponge is deformed by pressure and is inserted into the pores of the sponge.
Then in the glove box according to the novel no diaphragm structure design: the lithium metal battery is assembled by the negative electrode shell, the lithium sheet, the electrolyte, the sponge-lithium sheet negative electrode sheet, the gasket, the elastic sheet and the positive electrode shell. And finally, packaging the battery according to a conventional hydraulic packaging technology. All use the drift that the diameter was 10mm to dash out for the lithium sheet metal that the experiment was selected for use, and electrolyte all uses: 1M LiTFSI (DOL: DME ═ 1:1 vol%) +2 wt% LiNO3And the operations are all carried out in an argon glove box, wherein the water oxygen content is less than 0.1 ppm.
The test battery uses a conventional blue test channel, and during testing, the battery is discharged for 1h at a set current density and constant current, then is charged for 1h at the same current density, and the charge-discharge cycle is continuously repeated, wherein two current densities are set: 10mA/cm2；1mA/cm2. The stability of the battery cycling process and the inhibition effect of the sponge composite system on lithium dendrite are judged by observing the changes of potential and cycling time.
Referring to fig. 4, fig. 4 is a cycle test graph of a symmetrical battery designed with a sponge-metal lithium composite electrode non-separator structure prepared in example 1 and comparative example 1 of the present invention, and a cycle test comparison graph of a lithium metal symmetrical battery. As can be seen from fig. 4, at a large current density: 10mA/cm2The symmetrical battery with the sponge diaphragm-free structure shows more stable potential change along with the cycle time; likewise, at a low current density of 1mA/cm2Lower as a function of cycle time,More stable potential changes. Compared with the traditional lithium ion battery diaphragm, the sponge medium elastic interface layer and the three-dimensional structure thereof are more favorable for improving the cycle stability in the deposition and stripping processes of the metal lithium.
Comparative example 1
Polypropylene separator (Polypropylene) was used for assembly of conventional lithium metal batteries and comparative experiments for cycling tests of symmetric batteries:
with a conventional lithium metal battery structure: the lithium metal symmetric battery is assembled by the negative electrode shell, the lithium sheet, the PP diaphragm, the electrolyte, the lithium sheet, the gasket, the elastic sheet and the positive electrode shell, and then the battery is packaged according to the conventional hydraulic packaging technology. The lithium metal sheets selected for the experiment were all the same as in example 1 and punched out using a punch with a diameter of 10mm, and the electrolyte was used as follows: 1M LiTFSI (DOL: DME ═ 1:1 vol%) +2 wt% LiNO3The procedures described were all performed in an argon glove box and the method and conditions for testing half-cell cycles were the same as in example 1.
Example 2
Preparing a lithium metal battery with a sponge and metal lithium composite elastic interface material without a diaphragm structure design and testing the coulombic efficiency of a half-battery:
the sponge with the thickness of 2.5mm prepared in example 1 was used to prepare a novel composite electrode, and a novel lithium metal battery was assembled through a diaphragm-free structural design. The difference from example 1 is: the battery structure that test half-cell coulomb efficiency adopted does: the lithium battery comprises a negative electrode shell, a lithium sheet-sponge, electrolyte, a copper sheet, a gasket, an elastic sheet and a positive electrode shell. Referring to fig. 5, fig. 5 is a schematic structural view of a lithium metal battery (model: CR2032) with a diaphragm-free structural design of a sponge-metal lithium composite electrode assembled by testing coulombic efficiency in example 2 of the present invention.
The lithium metal sheet and the copper sheet selected in the experiment are punched by a punch with the diameter of 10mm, and the electrolyte is used as follows: 1M LiTFSI (DOL: DME ═ 1:1 vol%) +2 wt% LiNO3(ii) a All the operations are carried out in a glove box.
The coulombic efficiency of the half cell is tested by adopting a conventional blue light test system, which specifically comprises the following steps: standing the assembled lithium metal button battery for 12h, and then sealing the battery at a set currentDegree of 1mA/cm2Discharging for 1h, then setting the charging to cut off at the same current density until 1V, calculating the proportion of the charging capacity in the discharging capacity in the charging and discharging circulation process, and using the relation of the proportion value changing along with the time to evaluate the speed of the battery capacity attenuation. The results are shown in fig. 6, and fig. 6 is a coulomb efficiency test comparison graph of lithium metal half-cells with no separator structure design of sponge and metal lithium composite electrodes prepared in example 2 and comparative example 2 of the invention.
As can be seen from fig. 6, the elastic interface layer of the sponge no-separator structure design exhibited higher initial and average coulombic efficiency values during cycling compared to the Polypropylene separator (Polypropylene), which indicates that the sponge elastic interface layer and its three-dimensional structure had less lithium loss and "dead lithium" formation during cycling of the lithium metal battery compared to the conventional Polypropylene separator, and thus had higher metal lithium utilization during cycling.
Comparative example 2
Polypropylene separator (Polypropylene) was used for assembly of conventional lithium metal batteries and comparative experiments of coulomb efficiency testing of half-cells:
with a conventional lithium metal structure: and assembling the negative electrode shell, the lithium sheet, the polypropylene diaphragm, the copper sheet, the gasket, the elastic sheet and the positive electrode shell, and hydraulically packaging the lithium metal battery. The lithium metal sheet and the copper sheet selected in the experiment are punched by a punch with the diameter of 10mm, and the electrolyte is used as follows: 1MLiTFSI (DOL: DME ═ 1:1 vol%) +2 wt% LiNO3The procedure was similar to example 2, and the conditions for testing the coulombic efficiency of the half cell were the same as in example 2.
From the above embodiments, the present invention provides a novel lithium metal battery without a separator structure, and a sponge and lithium metal composite electrode material. The invention also provides an electrode plate and a lithium metal battery. The lithium metal battery is prepared by the electrode plate through a diaphragm-free structure design, and has good cycle stability and high coulombic efficiency. Moreover, the preparation process of the sponge and metal lithium composite material provided by the invention is simple and is suitable for large-scale industrial production.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Example 3
Preparing and testing the lithium metal half-cell with sponge and metal lithium composite elastic interface materials with different thicknesses and without diaphragm structure design:
in order to investigate the influence of sponge elastic interface layers with different thicknesses on the battery performance, under the same conditions, sponge materials with the thickness of 1mm before compression and the thickness of 4.5mm before compression are respectively adopted to assemble a half battery, and according to methods similar to those in examples 1 and 2, the coulombic efficiency and the cycle performance of the battery assembled by the sponges with different thicknesses under two conditions are respectively tested under the set current density.
Fig. 7 is a comparison of cycling and coulombic efficiency tests for half cells assembled with sponge elastic interface layers of different thicknesses as described in example 3 of the present invention. Wherein the left panel shows: the curve with dark black color is the cycle test result of a half cell assembled by sponge with the initial thickness of 2.5mm, and the lightest is the cycle test result with the smaller thickness of 1 mm; and the curve with larger intermediate potential value and fluctuation is the test result of 4.5mm of initial thickness. As can be seen from FIG. 7, among the three selected sponge materials, the sponge with the initial thickness of 2.5mm shows the optimal and most stable cycle performance, and effectively plays the role of the sponge elastic medium layer. The lithium metal half cell assembled by the sponge material with smaller thickness of 1mm has sharp change of potential after about 40 circles, and may be fluctuation caused by the formed lithium dendrite breaking the sponge medium layer. The sponge elastic medium layer with the thickness of 4.5mm shows obviously higher potential and more obvious fluctuation condition in the later period of the cycle, which is probably caused by that the excessively thick sponge medium layer increases the internal resistance of the lithium metal half cell and the unstable change of the reaction interface is generated.
Example 4
Preparing a lithium metal full battery with a sponge and metal lithium composite elastic interface material without a diaphragm structural design and testing the performance of the lithium metal full battery:
in order to verify the feasibility of the sponge and metal lithium composite elastic interface material, the LiFePO which is commercially available at present is selected4Assembling a full battery for the positive electrode material to test; the preparation process comprises the following steps of LiFePO4Coating a positive electrode material on an aluminum foil according to the proportion of PVDF to a conductive agent being 8:1:1, drying and weighing a punched sheet, and calculating the loading capacity of active substances as follows: 2.0 +/-0.25 mg/cm2。
The assembly process was similar to example 2 except that the copper foil was replaced with an aluminum foil coated with a positive electrode material. The test adopts blue test system, specifically includes: firstly, standing the assembled battery for 12 hours, firstly discharging to 2V at a multiplying power of 0.5C, and then charging to 3.8V at the same multiplying power; this process was repeated, and the capacity fade was observed, and the cycling performance of the cell was tested.
Fig. 8 is a graph of the first three cycles of cycling and coulombic efficiency testing of the full cell assembled with the sponge elastic interface layer described in example 4 of the present invention. As can be seen from FIG. 8, the specific capacity of the first ring of the full cell assembled by the sponge elastic medium layer and the lithium metal sheet was 125mAh/g (according to LiFePO)4Mass calculation of (c), and the average coulombic efficiency after 72 cycles of circulation reaches 96.1%; the application potential of the compound is proved.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.

Claims (8)

1. The lithium metal battery is characterized by comprising a positive electrode, a negative electrode and electrolyte, wherein a diaphragm is not included, the negative electrode is formed by applying physical pressing on a metal lithium sheet and sponge under the condition of protective atmosphere to form an elastic composite structure of a lithium layer-lithium/sponge transition layer-sponge layer, and when the lithium/sponge transition layer is formed by pressing the metal lithium sheet and the sponge, lithium is embedded into an elastic interface layer structure formed in pores of the sponge.
2. The lithium metal battery of claim 1, wherein the thickness of the lithium metal sheet is 50-1000 μm, the thickness of the sponge is 1-5 mm, and the thickness of the negative electrode sheet is 800-6000 μm.
3. The lithium metal battery according to claim 1, wherein the sponge has a density of 0.01 to 0.02g/cm3The porosity is 98-99%, and the pore diameter is 50-100 μm.
4. The lithium metal battery of claim 1, wherein the sponge is selected from one or more of a polyurethane sponge, a rubber sponge, and a melamine sponge.
5. The lithium metal battery of claim 1, wherein the method of making the negative electrode comprises the steps of:
and (3) under the condition of protective atmosphere, applying physical pressure to compound the sponge and the lithium sheet to obtain the negative electrode.
6. The lithium metal battery of claim 5, wherein the protective atmosphere conditions are selected from an argon atmosphere, and the water oxygen content in the protective atmosphere is less than 0.1 ppm.
7. The lithium metal battery of claim 1, wherein the electrolyte is selected from a lithium ion battery electrolyte or a lithium sulfur battery electrolyte.
8. The lithium metal battery of claim 1, wherein the positive electrode material of the positive electrode is selected from the group consisting of sulfur and conventional intercalation-type positive electrode materials: li4Ti5O12、LiFePO4、LiCoO2One or more of them.
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