CN110676420B - Lithium ion battery's lithium diaphragm of mending - Google Patents
Lithium ion battery's lithium diaphragm of mending Download PDFInfo
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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
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/409—Separators, membranes or diaphragms characterised by the material
- H01M50/431—Inorganic material
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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
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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
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/403—Manufacturing processes of separators, membranes or diaphragms
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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
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/409—Separators, membranes or diaphragms characterised by the material
- H01M50/411—Organic material
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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
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/409—Separators, membranes or diaphragms characterised by the material
- H01M50/449—Separators, membranes or diaphragms characterised by the material having a layered structure
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- 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
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- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Abstract
The invention provides a lithium supplement diaphragm of a lithium ion battery, which comprises a plurality of diaphragm layers which are mutually overlapped, wherein a metal lithium layer is arranged on each diaphragm layer, and a protective layer is also arranged above the metal lithium layer; the membrane layer is a polymer membrane. The lithium supplement diaphragm of the lithium ion battery can be directly used for pre-lithiation (lithium supplement) of the negative electrode of the lithium ion battery, so that the first coulombic efficiency and the cycle performance of the lithium ion battery are improved; the metal lithium layer is prevented from being etched by electrolyte and the ambient atmosphere, the irreversible chemical reaction between the metal lithium layer and the negative electrode active layer is avoided, and the efficiency of pre-lithiation or lithium supplement of the electrode is improved.
Description
Technical Field
The invention belongs to the field of lithium ion batteries, and particularly relates to a lithium supplement diaphragm of a lithium ion battery.
Background
Lithium ion batteries are widely used in human daily life as an efficient energy storage device. However, the conventional lithium ion battery cathode material is a graphite cathode, the theoretical specific capacity of the conventional lithium ion battery cathode material is only 372mAhg & lt-1 & gt, and the conventional lithium ion battery cathode material can no longer meet the requirements of a high-tech battery system. Therefore, development of high-performance and high-capacity negative electrodes is one of the major research directions in this field. The negative electrode materials such as Si base, SiO x and alloy have higher theoretical specific capacity, but the negative electrode materials generate larger volume change in the charging and discharging process, so that the electrode interface is very unstable, and the defects of low initial coulombic efficiency, poor cycle performance and the like of the battery are caused. By adding the carbon-based conductive agent into the high-energy cathode material, the stress deformation phenomenon of the electrode can be relieved to a certain extent, and the electronic conductivity of the electrode is improved. However, the first reversible capacity fade of the electrode still exists due to capacity loss resulting from a solid electrolyte film (SEI) formed at the surface of the electrode and the electrode active material itself, and greatly affects the performance of the battery in subsequent cycles. Therefore, pre-lithiation or lithium supplementation of the negative electrode is the most direct method to improve the performance of the negative electrode.
Methods for lithium supplement or prelithiation of negative electrodes can be divided into four categories: 1. an electrochemical prelithiation method; 2. a chemical prelithiation method; 3. a lithium metal pad method (contact method); 4. stable lithium metal powder process. Electrochemical methods are widely used as the original prelithiation technique, but this protocol is cumbersome to operate and energy intensive. The chemical method is simple to operate but has high operation danger, and particularly, the used lithium source is generally inflammable and explosive unstable substances, such as lithium tert-butoxide. The stable lithium metal powder method also has the disadvantages of high risk and high price. The lithium metal patch method (contact method) is currently the most industrially feasible method for lithium replenishment, but the minimum thickness of the sheet-like or foil-like lithium metal is 10 μm or more due to the problem of the softness of the lithium metal itself. The current commercial high-energy negative electrode surface capacity is 4mAhcm & lt-2 & gt, so that the lithium supplement amount of the negative electrode by the lithium metal patch method reaches multiple times of the self capacity of the negative electrode, the utilization rate of the lithium metal is reduced, and the cost of the lithium supplement negative electrode is increased. Therefore, there is an urgent need to provide a solution for preparing a lithium-compensated negative electrode with a controlled metallic lithium layer or a controlled degree of prelithiation. In addition, since metallic lithium has strong reducibility, irreversible chemical reaction occurs after the metallic lithium is contacted with the negative active layer, thereby etching the negative active layer to cause actual capacity fade. Therefore, there is a need to provide an efficient method to ensure the storage stability of the lithium supplement electrode sheet, so as to meet the requirement of industrial production.
Disclosure of Invention
In view of this, the present invention is directed to provide a lithium supplement separator for a lithium ion battery, which is directly used for pre-lithiation (lithium supplement) of a negative electrode of the lithium ion battery, so as to improve the first coulombic efficiency and cycle performance of the lithium ion battery.
In order to achieve the purpose, the technical scheme of the invention is realized as follows:
a lithium supplement diaphragm of a lithium ion battery comprises a plurality of diaphragm layers which are mutually overlapped, wherein a metal lithium layer is arranged on each diaphragm layer, and a protective layer is also arranged above each metal lithium layer; the membrane layer is a polymer membrane.
Further, the thickness of the protective layer is 0-300 nm; the protective layer is at least one of electron conductor particles, electron-ion mixed conductor particles, polymer materials, lithium oxides, lithium nitrides, lithium fluorides or lithium sulfides.
Furthermore, at least one of a diaphragm layer, a metal lithium layer or a protective layer is arranged on the protective layer.
Further, the polymer film is at least one of polyvinylidene chloride, polyvinylidene chloride-hexafluoropropylene, polytetrafluoroethylene, polyethylene oxide, polyester, polyamide imide, polymethyl methacrylate, polycarbonate, carboxymethyl cellulose, styrene-butadiene copolymer, polyacrylic acid, lithium polyacrylate, polyacrylonitrile, sodium carboxymethyl cellulose or styrene-butadiene rubber.
Further, a layer of conductor particles is disposed on one or both sides of the polymer film; the electronic conductor particles are at least one of carbon black, chrysene carbon, acetylene black, Super P, graphene, single-wall or multi-wall carbon nanotubes, copper powder, aluminum powder, natural graphite, artificial graphite, soft carbon, hard carbon, silicon, tin, germanium, zinc, aluminum, boron, magnesium or molybdenum dioxide; the ion-electron mixed conductor particles are at least one of natural graphite, artificial graphite, soft carbon, hard carbon, silicon, germanium, lithium titanate, titanium dioxide, copper oxide, zinc oxide, iron oxide, manganese oxide, tin oxide, stannous oxide, silicon monoxide, iron sulfide, lithium phosphate, lithium phosphorus oxygen nitrogen based amorphous solid electrolyte based on doped S, B, Si and C elements, ferrous sulfide, lithium phosphate, lithium phosphorus oxygen nitrogen or LiPON amorphous solid electrolyte based on doped S, B, Si and C elements.
Further, the thickness of the membrane layer is 10-100 μm; the number of the membrane layers is 1-10.
Further, the thickness of the metal lithium layer is 0.5-10 μm; the unit surface capacity of the metal lithium layer is 15-100% of the unit surface capacity of the corresponding negative active layer; the shape of the metal lithium layer is compact or porous and loose; the preparation method of the metal lithium layer and the protective layer is at least one of vacuum evaporation, ion plating, radio frequency sputtering, magnetron sputtering or reactive sputtering.
A lithium ion battery containing a lithium supplement diaphragm comprises a positive electrode, a negative electrode and the lithium supplement diaphragm, wherein the lithium supplement diaphragm is positioned between the positive electrode and the negative electrode, and a diaphragm layer is adjacent to the positive electrode.
Further, the number of the membrane layers is 1-5.
Further, the content of the metal lithium in the negative electrode is not more than one ten-thousandth of the mass per unit area of the active material layer of the negative electrode, and the electrode potential of the negative electrode with respect to the metal lithium is 1 to 4V.
The preparation method of the lithium-supplementing diaphragm comprises the following steps:
(1) placing the diaphragm layer in a vacuum cavity, wherein the horizontal distance between an evaporated lithium source and the diaphragm layer is 30-40cm, vacuumizing until the vacuum degree of the cavity reaches below 3 × 10-4 Pa, starting a cooling water circulation system, controlling the temperature of the diaphragm layer to be 20-30 ℃, and adjusting the power to be 50-200W;
(2) and placing the diaphragm with the surface deposited with the metal lithium layer in a magnetic control cavity, vacuumizing, adjusting the working pressure to 6 x 10-1 Pa when the vacuum degree reaches 10 < -5 > -10 < -3 > Pa, adjusting the horizontal distance between the lithium phosphate target material and the metal lithium layer on the surface of the diaphragm layer to 5cm, and controlling the flow ratio of the working gas N2 to Ar to be 3:1 by a mass flow controller to obtain the lithium supplement diaphragm with the protective layer on the surface.
The physical form of the evaporation lithium source is at least one of powder, particles, wires, sheets or ingots.
Compared with the prior art, the lithium supplement diaphragm of the lithium ion battery has the following advantages:
(1) the lithium supplement diaphragm of the lithium ion battery can be directly used for pre-lithiation (lithium supplement) of the negative electrode of the lithium ion battery, so that the first coulombic efficiency and the cycle performance of the lithium ion battery are improved; the metal lithium layer is prevented from being etched by electrolyte and the ambient atmosphere, the irreversible chemical reaction between the metal lithium layer and the negative electrode active layer is avoided, and the efficiency of pre-lithiation or lithium supplement of the electrode is improved.
(2) The lithium supplement diaphragm of the lithium ion battery avoids the damage to the negative electrode layer caused by the traditional pre-lithiation mode, avoids the use of a large amount of traditional pre-lithiation electrolyte, reduces the preparation steps of the pre-lithiation pole piece and avoids the side reaction of the lithium supplement pole piece in the storage process. The lithium-filled separator is a stand-alone product, and the excellent mechanical properties of the lithium-filled separator can support the roll-to-roll production mode.
Drawings
FIG. 1 is a schematic diagram of a lithium ion battery comprising a lithium-supplementing separator according to the present invention;
fig. 2 is a diagram of a separator layer and a lithium metal layer according to the present invention: 2-A: front view (no protective layer); 2-B: bottom view (no protective layer);
FIG. 3 is a diagram of a lithium-replenishing separator according to the present invention;
FIGS. 4-A to 4-D are SEM images of lithium-filled separators according to the present invention: 4-A: SEM picture of lithium-filled diaphragm under low magnification; 4-B: SEM picture of the front side of the lithium-supplementing diaphragm under high magnification; 4-C: SEM picture of the back of the lithium-supplementing diaphragm under low magnification; SEM image of the back of the lithium-filled separator at 4-D high magnification.
Fig. 5 is a graph of standing time versus open circuit voltage of a lithium ion battery comprising a lithium-complementary separator according to example 4 of the present invention.
Fig. 6 is a graph of the first coulombic efficiency of the lithium ion battery according to embodiment 4 of the present invention, which includes a lithium supplement separator;
FIG. 7 is a graph showing the cycle charge and discharge curves of a lithium ion battery comprising a lithium-complementary separator according to example 4 of the present invention;
FIG. 8 is a graph of the first coulombic efficiency of a lithium ion battery according to comparative example 1 of the present invention;
fig. 9 is a graph showing the cycle charge and discharge of the lithium ion battery according to comparative example 1 of the present invention.
Description of reference numerals:
1-a separator layer; 2-a layer of metallic lithium; 3-a protective layer; 4-a negative active layer; 5-positive electrode active layer; 6-negative current collector; 7-positive electrode current collector.
Detailed Description
Unless defined otherwise, technical terms used in the following examples have the same meanings as commonly understood by one of ordinary skill in the art to which the present invention belongs. The test reagents used in the following examples, unless otherwise specified, are all conventional biochemical reagents; the experimental methods are conventional methods unless otherwise specified.
The present invention will be described in detail with reference to the following examples and accompanying drawings.
Example 1
The lithium supplement diaphragm of the lithium ion battery comprises a plurality of diaphragm layers which are mutually overlapped, wherein a metal lithium layer is arranged on each diaphragm layer, and a protective layer is also arranged above each metal lithium layer.
The membrane layer is a single-layer polypropylene membrane with the thickness of 20 mu m. The protective layer adopts LiPON with the thickness of 10 nm. The thickness of the lithium metal layer was 3 μm.
The preparation method of the lithium-supplementing diaphragm comprises the following steps:
(1) placing the diaphragm layer in a vacuum cavity, wherein the horizontal distance between an evaporated lithium source and the diaphragm layer is 40cm, vacuumizing until the vacuum degree of the cavity reaches below 3 x 10-4 Pa, starting a cooling water circulation system to ensure that the temperature of the diaphragm layer is controlled at 20-30 ℃, wherein the physical form of the used evaporated lithium material is a lithium ingot, adjusting the power range to be 50-200W, detecting in real time through a quartz crystal oscillator to accurately control the thickness of the metal lithium layer, and finishing the reaction, wherein the thickness of the metal lithium layer on the surface of the lithium-supplement diaphragm is 3 mu m.
(2) And (2) placing the diaphragm with the surface deposited with the metal lithium layer obtained in the step (1) in a magnetic control cavity, vacuumizing, adjusting the working pressure to 6 x 10-1 Pa when the vacuum degree reaches 10-5-10-3 Pa, adjusting the horizontal distance between the lithium phosphate target and the metal lithium layer on the surface of the diaphragm layer to 5cm, controlling the flow ratio of the working gas N2 to Ar to be 3:1 by a mass flow controller, and depositing a LiPON protective layer with the thickness of 10nm on the surface of the metal lithium layer after a period of time to obtain the lithium supplement diaphragm with the LiPON protective layer on the surface.
As shown in fig. 2, the front surface of the lithium supplement diaphragm shows a uniform lithium metal phase, and the back surface of the lithium supplement diaphragm does not have a lithium metal phase and a damage crack, which indicates that the lithium supplement diaphragm prepared by the vacuum thermal evaporation method does not damage the diaphragm layer substrate, and the lithium metal layer prepared by the physical deposition method is relatively uniform.
The protective layer covers the surface of the metal lithium layer, so that the active metal lithium layer can be prevented from being etched by a non-inert atmosphere, as shown in fig. 3, the front surface of the lithium supplement diaphragm which is kept stand for a period of time under the non-inert atmosphere under the protection of the LiPON still presents the color of the metal lithium, the effect between the metal lithium layer and the external environment is effectively isolated by the LiPON layer, and the storage stability of the lithium supplement diaphragm is improved. As shown in fig. 4-a and 4-B, SEM photographs of the front surface of the lithium supplement separator prepared in step 3) show that the structure of the metal lithium layer (including the protective layer) on the surface of the separator layer is porous and loose, which is beneficial to wetting with an electrolyte and improving the activity of an electrochemical reaction. Meanwhile, as shown in fig. 4-C and 4-D, SEM photographs of the back surface of the lithium supplement separator prepared in step 3) show that no metallic lithium phase is found on the back surface of the lithium supplement separator layer, which indicates that the deposited metallic lithium does not pass through the pore structure in the separator layer during the preparation of the lithium supplement separator by the vacuum thermal evaporation method.
Example 2
The lithium supplement diaphragm of the lithium ion battery comprises a plurality of diaphragm layers which are mutually overlapped, wherein a metal lithium layer is arranged on each diaphragm layer, and a protective layer is also arranged above each metal lithium layer.
The membrane layer is a single-layer polypropylene membrane with the thickness of 20 mu m. The protective layer is made of Al and is 10nm thick. The thickness of the lithium metal layer was 3 μm.
The preparation method of the lithium-supplementing diaphragm comprises the following steps:
(1) placing the diaphragm layer in a vacuum cavity, wherein the horizontal distance between an evaporated lithium source and the diaphragm layer is 40cm, vacuumizing until the vacuum degree of the cavity reaches below 3 x 10-4 Pa, starting a cooling water circulation system to ensure that the temperature of the diaphragm layer is controlled at 20-30 ℃, wherein the physical form of the used evaporated lithium material is a lithium sheet, adjusting the power range to be 50-200W, detecting in real time through a quartz crystal oscillator to accurately control the thickness of the metal lithium layer, and finishing the reaction, wherein the thickness of the metal lithium layer on the surface of the lithium-supplement diaphragm is 3 mu m.
(2) And (2) placing the diaphragm with the surface deposited with the metal lithium layer obtained in the step (1) in an evaporation chamber, vacuumizing, wherein the horizontal distance between an evaporation aluminum source and a pole piece is 30cm, vacuumizing until the vacuum degree of the chamber reaches below 3 x 10-4 Pa, and the physical form of the evaporated aluminum material is aluminum particles. Adjusting the power range to be 50-100W, detecting in real time through a quartz crystal oscillator to realize accurate control of the thickness of the protective layer, and depositing an Al protective layer with the thickness of 10nm on the surface of the metal lithium layer after a period of time to obtain the lithium supplement diaphragm with the Al protective layer on the surface.
Example 3
The lithium supplement diaphragm of the lithium ion battery comprises a plurality of diaphragm layers which are mutually overlapped, wherein a metal lithium layer is arranged on each diaphragm layer, and a protective layer is also arranged above each metal lithium layer.
The membrane layer is a single-layer PP with the surface coated with aluminum oxide, and the thickness of the membrane layer is 40 mu m. The protective layer adopts LiPON with the thickness of 10 nm. The thickness of the lithium metal layer was 3 μm.
The preparation method of the lithium-supplementing diaphragm comprises the following steps:
(1) placing the diaphragm layer in a vacuum cavity, wherein the horizontal distance between an evaporated lithium source and the diaphragm layer is 30cm, vacuumizing until the vacuum degree of the cavity reaches below 3 x 10-4 Pa, starting a cooling water circulation system to ensure that the temperature of the diaphragm layer is controlled at 20-30 ℃, wherein the physical form of the used evaporated lithium material is a lithium sheet, adjusting the power range to be 50-200W, detecting in real time through a quartz crystal oscillator to accurately control the thickness of the metal lithium layer, and finishing the reaction, wherein the thickness of the metal lithium layer on the surface of the lithium-supplement diaphragm is 3 mu m.
(2) And (2) placing the diaphragm with the surface deposited with the metal lithium layer obtained in the step (1) in a magnetic control cavity, vacuumizing, adjusting the working pressure to 6 x 10-1 Pa when the vacuum degree reaches 10-5-10-3 Pa, adjusting the horizontal distance between the lithium phosphate target and the metal lithium layer on the surface of the diaphragm layer to 5cm, controlling the working gas Ar through a mass flow controller, and depositing a LiPON protective layer with the thickness of 10nm on the surface of the metal lithium layer after a period of time to obtain the lithium supplement diaphragm with the LiPON protective layer on the surface.
(3) And (3) depositing and preparing a second unit structure on the surface of the lithium supplement diaphragm of the unit in the step (2) to obtain the multi-stage lithium supplement diaphragm with the structure of diaphragm layer-metal lithium layer-protective layer. Wherein the total thickness of the metal lithium layer is 6 μm, and the total thickness of the protective layer is 20 nm.
Example 4
A lithium-supplementing diaphragm battery comprises a positive electrode, a negative electrode and the lithium-supplementing diaphragm in embodiment 1, wherein the lithium-supplementing diaphragm is positioned between the positive electrode and the negative electrode, and the diaphragm layer is adjacent to the positive electrode.
The preparation method of the lithium-supplement diaphragm battery comprises the following steps:
(1) preparation of lithium-filled separator the procedure for example 1;
(2) the positive active material is lithium iron phosphate;
(3) the positive electrode active material powder is placed in a forced air drying oven and treated at 70 ℃ for 24 hours to remove moisture in the powder, and then the positive electrode powder, the conductive agent carbon black and PVDF are mixed according to a mass ratio of 90: 5: 5 mixing the positive electrode slurry with a solvent NMP to prepare viscous positive electrode slurry;
(4) the positive current collector adopts a pure aluminum foil with the thickness of 16 mu m, before the positive current collector is used, the aluminum current collector is subjected to ultrasonic cleaning in acetone to remove grease, and then the aluminum current collector is placed in an Ar ion cleaning instrument to remove impurities on the surface of the current collector;
(5) coating the positive electrode slurry prepared in the step 3) on the upper surface of the aluminum current collector in the step 4), and placing the aluminum current collector in a forced air drying oven for processing at 100 ℃ for 24 hours to obtain a positive electrode piece with a positive electrode active layer;
(6) taking the positive pole piece prepared in the step 5), and carrying out rolling treatment, wherein the compaction density is 2-3mg/cm & lt 3 & gt;
(7) the negative active material may be a silica/graphite composite material;
(8) the negative electrode active material powder is placed in a forced air drying oven for 24 hours at 70 ℃ to remove moisture in the powder, and then the negative electrode powder, the conductive agent carbon black, CMC and SBR are mixed according to a mass ratio of 85: 5: 7: 3 mixing the mixture with solvent water to prepare viscous negative electrode slurry;
(9) the negative current collector adopts a pure copper foil with the thickness of 12 current collectors, before the negative current collector is used, the C mu current collector is subjected to ultrasonic cleaning in acetone to remove grease, and then the C mu current collector is placed in an Ar ion cleaning instrument to remove impurities on the surface of the current collector;
(10) and (3) coating the upper surface of the copper current collector in the step (9) with the negative electrode slurry prepared in the step (8), and placing the copper current collector in a forced air drying oven for 24 hours at 70 ℃ to obtain a negative electrode piece with a negative electrode active layer thickness of 125 microns.
(11) Taking the negative pole piece prepared in the step 10), carrying out rolling treatment, wherein the compaction density of the silicon oxide/graphite electrode is 0.2-0.5mg/cm & lt 3 & gt, and then cutting the pole piece into a fixed size.
Assembling the lithium ion battery:
(12) the battery includes: the lithium supplement diaphragm described in example 1, the positive electrode sheet described in step 6), the negative electrode sheet described in step 11), a lithium ion battery electrolyte and a battery case are commonly used, and the battery is assembled according to the structure shown in fig. 1, wherein one side of a metal lithium layer in the lithium supplement diaphragm is attached to a negative electrode active layer.
As shown in fig. 5, the initial open circuit potential of the full cell using lithium iron phosphate for the positive electrode and silicon oxide/graphite for the negative electrode was about 3.2V, because the potential difference between the positive and negative electrodes was increased by the metallic lithium layer in the lithium-supplemented separator. After standing for 500 hours, the open-circuit voltage of the battery is about 2.5V, which shows that the self-discharge reaction of the lithium metal layer and the negative active layer in the lithium-supplement diaphragm is small under the action of the protective layer. The first coulombic efficiency of the lithium ion battery with the lithium-supplement diaphragm can be shown in fig. 6. The first coulombic efficiency of the lithium ion battery with the lithium supplement diaphragm is higher than 95%, which shows that the metal lithium layer in the lithium supplement diaphragm has the function of compensating the reversible capacity loss of the negative electrode. Fig. 7 shows the cycle charge and discharge performance of the lithium ion battery adopting the lithium supplement diaphragm, and it can be seen that the cycle performance, the capacity retention rate and the coulomb efficiency of the battery are obviously improved under the action of the lithium supplement diaphragm.
Example 5
The soft package lithium ion battery with the lithium supplement diaphragm comprises a positive electrode, a negative electrode and the lithium supplement diaphragm, wherein the lithium supplement diaphragm is positioned between the positive electrode and the negative electrode, and a diaphragm layer is adjacent to the positive electrode.
The lithium supplement diaphragm of the lithium ion battery comprises a plurality of diaphragm layers which are mutually overlapped, wherein a metal lithium layer is arranged on each diaphragm layer, and a protective layer is also arranged above each metal lithium layer.
The membrane layer is three layers of PP/PE/PP, and the thickness of the membrane layer is 50 mu m. The protective layer adopts LiPON and has the thickness of 3 nm. The thickness of the lithium metal layer was 4 μm.
The preparation method of the lithium-supplementing diaphragm comprises the following steps:
(1) placing the diaphragm layer in a vacuum cavity, wherein the horizontal distance between an evaporated lithium source and the diaphragm layer is 30cm, vacuumizing until the vacuum degree of the cavity reaches below 3 x 10-4 Pa, starting a cooling water circulation system to ensure that the temperature of the diaphragm layer is controlled at 20-30 ℃, wherein the physical form of the used evaporated lithium material is a lithium sheet, adjusting the power range to be 50-200W, detecting in real time through a quartz crystal oscillator to accurately control the thickness of the metal lithium layer, and finishing the reaction, wherein the thickness of the metal lithium layer on the surface of the lithium-supplement diaphragm is 4 mu m.
(2) And (2) placing the diaphragm with the surface deposited with the metal lithium layer obtained in the step (1) in a magnetic control cavity, vacuumizing, adjusting the working pressure to 6 x 10-1 Pa when the vacuum degree reaches 10-5-10-3 Pa, adjusting the horizontal distance between the lithium phosphate target and the metal lithium layer on the surface of the diaphragm layer to 5cm, controlling the working gas Ar through a mass flow controller, and depositing a LiPON protective layer with the thickness of 8nm on the surface of the metal lithium layer after a period of time to obtain the lithium supplement diaphragm with the LiPON protective layer on the surface.
The positive active material is lithium iron phosphate;
(3) the positive electrode active material powder is placed in a forced air drying oven and treated at 70 ℃ for 24 hours to remove moisture in the powder, and then the positive electrode powder, the conductive agent carbon black and PVDF are mixed according to a mass ratio of 90: 5: 5 mixing the positive electrode slurry with a solvent NMP to prepare viscous positive electrode slurry;
(4) the positive current collector adopts a pure aluminum foil with the thickness of 16 mu m, before the positive current collector is used, the aluminum current collector is subjected to ultrasonic cleaning in acetone to remove grease, and then the aluminum current collector is placed in an Ar ion cleaning instrument to remove impurities on the surface of the current collector;
(5) coating the positive electrode slurry prepared in the step 3) on the upper surface of the aluminum current collector in the step 4), and placing the aluminum current collector in a forced air drying oven for processing at 100 ℃ for 24 hours to obtain a positive electrode piece with a positive electrode active layer;
(6) and (3) rolling the positive pole piece prepared in the step 5), wherein the compaction density is 2-3mg/cm & lt 3 & gt, and the thickness of the positive active layer is 250 micrometers.
(7) The negative active material may be a silica/graphite composite material;
(8) the negative electrode active material powder is placed in a forced air drying oven for 24 hours at 70 ℃ to remove moisture in the powder, and then the negative electrode powder, the conductive agent carbon black, CMC and SBR are mixed according to a mass ratio of 85: 5: 7: 3 mixing the mixture with solvent water to prepare viscous negative electrode slurry;
(9) the negative current collector adopts a pure copper foil with the thickness of 12 current collectors, before the copper foil is used, the Cu current collector is subjected to ultrasonic cleaning in acetone to remove grease, and then the copper foil is placed in an Ar ion cleaning instrument to remove impurities on the surface of the current collector;
(10) and (3) coating the upper surface of the copper current collector in the step (9) with the negative electrode slurry prepared in the step (8), and placing the copper current collector in a forced air drying oven for 24 hours at 70 ℃ to obtain a negative electrode piece with a negative electrode active layer thickness of 125 microns.
(11) And (3) rolling the negative pole piece prepared in the step 10), wherein the compaction density of the silicon oxide/graphite electrode is 0.2-0.5mg/cm & lt 3 & gt, and the thickness of the negative pole active layer is 250 micrometers. The pole pieces are then cut to a fixed size.
Assembling the lithium ion battery:
(12) the battery includes: the lithium supplementing diaphragm in the step 2), the positive pole piece in the step 6) and the negative pole piece in the step 11) are commonly used for lithium ion battery electrolyte, an aluminum plastic film and positive and negative pole tabs, wherein one side of a metal lithium layer in the lithium supplementing diaphragm is attached to a negative active layer. The soft package battery is combined by adopting a mode of 5 positive pole pieces and 6 negative pole pieces.
The first coulombic efficiency of the soft package lithium ion battery with the lithium supplement diaphragm is 98%, and the capacity retention rate after 200 cycles is 91%, which shows that the lithium supplement diaphragm also has feasibility in the soft package lithium ion battery system and can compensate the capacity loss of the negative electrode.
Comparative example 1
A lithium ion battery comprises a positive electrode, a negative electrode, a diaphragm, a battery shell and a common lithium ion electrolyte, wherein the positive electrode adopts a lithium iron phosphate positive electrode in embodiment 4, the negative electrode adopts a silicon monoxide/graphite negative electrode in embodiment 4, and the diaphragm adopts single-layer PP with the thickness of 20 mu m. As shown in fig. 9, after the lithium ion battery without the lithium supplement separator is charged and discharged for the first time, the corresponding first coulombic efficiency is lower than 40%. And under the condition that the lithium supplement diaphragm is not used, the cycle performance and the capacity retention rate of the battery are poor, and as shown in figure 9, the specific discharge capacity of the battery in the second cycle is lower than 50mAh g < -1 >.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (9)
1. A lithium filling diaphragm of a lithium ion battery is characterized in that: the lithium-supplementing diaphragm comprises a plurality of diaphragm layers which are mutually overlapped, and a metal lithium layer and a protective layer are sequentially arranged on the diaphragm layers; the membrane layer is a polymer membrane;
the protective layer is also provided with a metal lithium layer and a protective layer;
one side of the metal lithium layer in the lithium supplement diaphragm is attached to the negative active layer.
2. The lithium-supplementing separator for a lithium ion battery according to claim 1, wherein: the thickness of the protective layer is 0-300 nm; the protective layer is at least one of electron conductor particles, electron-ion mixed conductor particles, polymer materials, lithium oxides, lithium nitrides, lithium fluorides or lithium sulfides.
3. The lithium-supplementing separator for a lithium ion battery according to claim 1, wherein: the polymer film is at least one of polyvinylidene chloride, polyvinylidene chloride-hexafluoropropylene, polytetrafluoroethylene, polyethylene oxide, polyester, polyamide imide, polymethyl methacrylate, polycarbonate, carboxymethyl cellulose, styrene-butadiene copolymer, polyacrylic acid, lithium polyacrylate, polyacrylonitrile, sodium carboxymethyl cellulose or styrene-butadiene rubber.
4. The lithium-supplementing separator for a lithium ion battery according to claim 1 or 2, wherein: a layer of conductor particles is arranged on one side or both sides of the polymer film; the conductor particle layer is at least one of ion conductor particles, electron conductor particles or ion-electron mixed conductor particles; the electronic conductor particles are at least one of carbon black, chrysene carbon, acetylene black, SuperP, graphene, single-wall or multi-wall carbon nanotubes, copper powder, aluminum powder, natural graphite, artificial graphite, soft carbon, hard carbon, silicon, tin, germanium, zinc, aluminum, boron, magnesium or molybdenum dioxide; the ion-electron mixed conductor particles are at least one of natural graphite, artificial graphite, soft carbon, hard carbon, silicon, germanium, lithium titanate, titanium dioxide, copper oxide, zinc oxide, iron oxide, manganese oxide, tin oxide, stannous oxide, silicon monoxide, iron sulfide, ferrous sulfide, lithium phosphate, lithium phosphorus oxygen nitrogen or lithium phosphorus oxygen nitrogen amorphous solid electrolyte based on doped S, B, Si and C elements.
5. The lithium-supplementing separator for a lithium ion battery according to claim 1, wherein: the thickness of the membrane layer is 10-100 μm; the number of the membrane layers is 1-10.
6. The lithium-supplementing separator for a lithium ion battery according to claim 1, wherein: the thickness of the metal lithium layer is 0.5-10 μm; the unit surface capacity of the metal lithium layer is 15-100% of the unit surface capacity of the corresponding negative active layer; the shape of the metal lithium layer is compact or porous and loose; the preparation method of the metal lithium layer and the protective layer is at least one of vacuum evaporation, ion plating, radio frequency sputtering, magnetron sputtering or reactive sputtering.
7. A lithium ion battery comprising a lithium-replenishing separator, characterized in that: the lithium-supplementing separator comprises a positive electrode, a negative electrode and the lithium-supplementing separator as claimed in any one of claims 1 to 6, wherein the lithium-supplementing separator is positioned between the positive electrode and the negative electrode, and the separator layer is adjacent to the positive electrode.
8. The lithium ion battery of claim 7, wherein: the number of the membrane layers is 1-5.
9. The lithium ion battery of claim 7, wherein: the content of the metal lithium in the negative electrode is less than or equal to one ten-thousandth of the mass per unit area of the active material layer of the negative electrode, and the electrode potential of the negative electrode relative to the metal lithium is 1-4V.
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| CN116053708B (en) * | 2023-03-29 | 2023-07-04 | 安迈特科技(北京)有限公司 | Lithium supplementing composite diaphragm for lithium battery, lithium battery and preparation method of lithium battery |
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