CN112652738A

CN112652738A - Lithium supplementing method of lithium ion battery

Info

Publication number: CN112652738A
Application number: CN201910997308.0A
Authority: CN
Inventors: 宋远志
Original assignee: Huaiyin Normal University
Current assignee: Huaiyin Normal University
Priority date: 2019-10-12
Filing date: 2019-10-12
Publication date: 2021-04-13

Abstract

The invention discloses a lithium supplementing method of a lithium ion battery, which is characterized in that porous metal lithium is arranged between a negative electrode material and a diaphragm of the lithium ion battery to be used as a negative electrode of the battery, and a lithium-containing positive electrode material (such as lithium iron phosphate and the like) is used as a positive electrode of the battery to assemble a full battery, so that the capacity of the battery can be greatly improved, the polarization generated by lithium shortage of the positive electrode can be reduced, and the performance of the battery can be improved.

Description

Lithium supplementing method of lithium ion battery

Technical Field

The invention belongs to the field of energy.

Background

The lithium ion battery has the advantages of large capacity, large energy density, safe use, environmental protection, long service life and the like, and is a preferred product of the power battery, but because the voltage of the battery in the discharging process can not be set to be 0V, for example, the discharging voltage of the lithium iron phosphate-graphite battery is usually set to be more than 2V, a large amount of lithium stored in graphite can not be separated, and the actual capacity of the battery is far smaller than the theoretical capacity of the battery; in addition, in the discharge process of the graphite cathode electrode, Li can continuously permeate into the graphite cathode material and form a film on the surface of the graphite cathode electrode, and more Li is accumulated in the cathode along with the increase of the discharge times until the lithium battery reaches saturation, so that the discharge capacity of the battery is continuously attenuated, and the energy density is continuously reduced. In addition, when the concentration of lithium ions in the battery is reduced, the concentration of the lithium ions in the lithium iron phosphate anode material is greatly reduced, so that the resistance of the lithium iron phosphate anode material is greatly increased, the polarization of the battery is serious, the charging and discharging of the battery are seriously interfered, and the performance of the battery is greatly reduced.

The invention provides a method for supplementing lithium to the positive electrode of a battery made of a lithium-containing positive electrode material such as lithium iron phosphate, lithium cobaltate, lithium manganate, ternary lithium and the like. The principle is that a proper amount of lithium materials such as porous metal lithium or lithium belts or lithium wires or lithium powder and the like are placed between a lithium battery diaphragm and a negative electrode material, and the lithium materials are charged and discharged with low current, so that the metal lithium in the diaphragm is dissolved and stored in the negative electrode material, and the purpose of improving the capacity of the lithium ion battery is achieved.

Disclosure of Invention

In order to obtain a high-performance lithium ion battery, the invention is implemented by the following technical scheme: (1) firstly, preparing materials such as porous metal lithium sheets or lithium belts or lithium wires to prepare a lithium net, which is beneficial to ions to pass through to generate current and is used as an auxiliary electrode of a negative electrode; (2) uniformly mixing a positive material such as lithium iron phosphate and the like, an adhesive and a conductive agent, coating the mixture on an aluminum foil to form a positive electrode, uniformly mixing a negative material such as graphite and the like, the adhesive and the conductive agent, coating the mixture on a copper foil to form a negative electrode, performing vacuum drying on the electrode at 80 ℃, placing porous metal lithium between a diaphragm and the negative electrode, and forming a battery by using a conventional method by using a lithium hexafluorophosphate-carbonate mixed solution as an electrolyte; (3) and small current is adopted for 1-10 times of charge and discharge, the metal lithium is converted into lithium ions which are slowly injected into the negative electrode and reduced into lithium, and the battery can be normally used.

The invention further improves the scheme as follows:

1. the porous or mesh-like lithium sheet can be prepared by casting, mechanical punching, drilling, laser drilling, or lithium wire weaving.

2. The mass and the grid size of the lithium metal mesh can be selected according to the capacity of the battery.

3. Other methods can also be adopted to form porous lithium on the surface of the negative electrode, such as adding a lithium belt or a lithium wire or lithium powder on the surface to form net lithium, or vacuum thermal spraying lithium, or heating and melting lithium spray by an organic solvent, or lithium magnetic sputtering, or electrolytic reduction of lithium ions and other methods.

4. The prepared battery adopts small current of 0.1-1.0mA/cm for 1-10 times of charge and discharge²And the lithium ions are prevented from reacting too fast in the negative electrode channel to generate metal lithium, and the lithium ions are prevented from permeating to the deep part of the negative electrode.

5. For lithium-containing anode materials such as lithium iron phosphate, lithium cobaltate, lithium manganate, ternary lithium and the like, the discharge voltage is set to be about 2V, so that the complete oxidation of the metal lithium of the cathode is prevented, and the ion channel of the cathode is prevented from being blocked.

The invention has the beneficial effects that: according to the manufacturing method of the battery, the advantages of the battery can be seen as follows:

1. the preparation method of the battery is simple, has little influence on the existing lithium battery production process, is safe to operate and is convenient for large-scale production.

2. Under the same condition, the battery assembled by the lithium iron phosphate anode material has greatly improved discharge capacity and obviously improved charge and discharge performance.

Detailed Description

1、LiFePO₄A lithium-rich battery: 2032 stainless steel button cell case, 0.2g of commercial carbonized LiFePO₄The lithium ion battery is prepared by taking commercially available natural graphite as a positive electrode material, taking electroactive material, PVDF adhesive and carbon black as negative electrode materials according to the ratio of 80: 10: 20, taking 1M lithium hexafluorophosphate as electrolyte (the solvent is methyl carbonate, ethylene carbonate and dimethyl carbonate in the ratio of 1: 1), taking aluminum foil as a positive current collector, taking copper foil as a negative current collector, taking glass fiber with the thickness of 1mm and the aperture of 7um as a battery diaphragm, and inserting lithium foil with the thickness of 0.1mm and the aperture of 1mm and the aperture distance of 1mm between the battery diaphragm and the negative electrode to assemble the battery. After the battery is sealed, discharging the battery with 0.1-1mA current until the voltage is 2V, and then charging the battery with 0.1-1mA current to 4V; after the second time, the discharge termination voltage is 2 volts, the charge voltage is 4 volts, and the charge and discharge current is 1mA, and the cycle is performed for 50 times.

2、LiFePO₄Battery comparative experiments: 2032 stainless steel button cell case, 0.2g of commercial LiFePO was used₄Is a positive electrode material (and

5 materials are the same), and commercial graphite is used as a negative electrode material. The electroactive material, PVDF adhesive and carbon black are prepared according to the ratio of 80: 10: 20, 1M lithium hexafluorophosphate is used as electrolyte (the solvent is methyl carbonate, ethylene carbonate and dimethyl carbonate with the ratio of 1: 1), aluminum foil is used as a positive current collector, copper foil is used as a negative current collector, glass fiber with the thickness of 1mm and the aperture of 7um is used as a battery diaphragm, and the battery is assembled. After the battery is sealed, the charging voltage is 4 volts, the discharging voltage is 2 volts, and the charging and discharging current is 1-2mA for 50 cycles.

Drawings

FIG. 1(a) shows lithium-rich LiFePO₄Charge-discharge curves of Li cells, FIG. 1(b) shows Li-rich LiFePO₄Specific discharge capacity and charge-discharge efficiency of Li cells, high cell current 0.2mA/cm²And (3) charging and discharging, wherein the specific capacity of the working state voltage of 2-4V is about 140mAh/g, the charging and discharging efficiency is 97-102%, and the discharging platform is about 3.3V. FIG. 1(c) shows LiFePO₄X-ray powder diffraction pattern (XRD) of (A), FIG. 1(d) is LiFePO₄Scanning Electron Micrograph (SEM).

FIG. 2(a) shows LiFePO₄Li vs. the charge-discharge curve of the cell, FIG. 2(b) for LiFePO₄Li vs discharge specific capacitance and charge-discharge efficiency of the battery, high current of 0.2mA/cm²And (3) charging and discharging, wherein the specific capacity of the battery in the working state voltage of 2-4V is about 24mAh/g, the charging and discharging efficiency is 95-105%, and the discharging platform is about 2.9V.

FIG. 3(a) shows lithium-rich LiFePO₄AC impedance diagram of Li cell, FIG. 3(b) is LiFePO₄The ac impedance plot of the Li versus cell, the contact and mass transfer impedances of the lithium-rich lithium iron phosphate cell are much lower than those of the comparative cell, indicating that the performance of the lithium-rich lithium iron phosphate cell is significantly improved.

Claims

1. In order to obtain the high-performance lithium secondary battery, porous metal lithium is placed on the interface of a battery negative electrode and a diaphragm to serve as an auxiliary negative electrode of the electrode, lithium-containing materials such as lithium iron phosphate and the like, adhesives and conductive agents are mixed and coated on aluminum foil to serve as a positive electrode, negative materials such as graphite and the like, adhesives and conductive agents are mixed and coated on copper foil to serve as a negative electrode, the electrode is subjected to vacuum drying, lithium hexafluorophosphate carbonate mixed liquid and the like serve as electrolytes, and the battery is formed according to a conventional method.

2. The porous or mesh-like lithium sheet can be prepared by casting, mechanical punching, drilling, laser drilling, or lithium wire weaving. Other methods can also be adopted to form porous lithium on the surface of the negative electrode, such as adding a lithium belt or a lithium wire or lithium powder on the surface to form net lithium, thermally spraying lithium in vacuum, heating and melting lithium by an organic solvent, spraying lithium by magnetic sputtering, electrolyzing and reducing lithium ions and the like.

3. The quality, the grid size and the size of the lithium metal mesh can be designed according to the capacity of the battery.

4. The battery is charged and discharged for 1-10 times by 0.1-1.0mA/cm²And (3) converting the metal lithium into lithium ions, slowly injecting the lithium ions into the negative electrode and reducing the lithium ions into lithium by a small current.