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CN108550835B - Lithium iron phosphate/gel electrolyte composite positive electrode material and preparation method thereof, and solid-state lithium battery and preparation method thereof - Google Patents

Lithium iron phosphate/gel electrolyte composite positive electrode material and preparation method thereof, and solid-state lithium battery and preparation method thereof Download PDF

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CN108550835B
CN108550835B CN201810558684.5A CN201810558684A CN108550835B CN 108550835 B CN108550835 B CN 108550835B CN 201810558684 A CN201810558684 A CN 201810558684A CN 108550835 B CN108550835 B CN 108550835B
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lithium
iron phosphate
lithium iron
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electrolyte
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CN108550835A (en
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王秀丽
张晟昭
涂江平
夏新辉
谷长栋
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Hangzhou Yishengda New Energy Technology Co ltd
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Shandong Industrial Technology Research Institute of ZJU
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
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    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
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Abstract

本发明提供了一种磷酸铁锂/凝胶电解质复合正极材料及其制备方法。本发明在制备复合正极材料过程中，将磷酸铁锂粉体和导电炭黑以及锂盐溶液等以均质浆料的形式涂覆在集流体上再进行紫外光固化，使得电解质均匀地包覆在磷酸铁锂纳米颗粒表面，实现了磷酸铁锂粉体表面均匀的包覆凝胶电解质，实现了正极材料与电解质分子级别的结合，从而显著增大了电解质和磷酸铁锂之间的接触面积，促进了锂离子的转移和传输，减小了电极的极化和界面阻抗。本发明还提供了一种采用上述技术方案所述正极得到的固态锂电池。

Figure 201810558684

The invention provides a lithium iron phosphate/gel electrolyte composite positive electrode material and a preparation method thereof. In the present invention, in the process of preparing the composite positive electrode material, the lithium iron phosphate powder, conductive carbon black and lithium salt solution are coated on the current collector in the form of homogeneous slurry and then cured by ultraviolet light, so that the electrolyte is evenly coated On the surface of the lithium iron phosphate nanoparticles, the uniform coating of the gel electrolyte on the surface of the lithium iron phosphate powder is realized, and the combination of the positive electrode material and the electrolyte at the molecular level is realized, thereby significantly increasing the contact area between the electrolyte and lithium iron phosphate. , which promotes the transfer and transport of lithium ions and reduces the polarization and interface impedance of the electrode. The present invention also provides a solid-state lithium battery obtained by using the positive electrode described in the above technical solution.

Figure 201810558684

Description

Lithium iron phosphate/gel electrolyte composite positive electrode material and preparation method thereof, and solid-state lithium battery and preparation method thereof
Technical Field
The invention belongs to the technical field of solid-state lithium batteries, and particularly relates to a lithium iron phosphate/gel electrolyte composite positive electrode material and a preparation method thereof, and a solid-state lithium battery and a preparation method thereof.
Background
With the continuous development of global economy and the continuous improvement of the living standard of people, the energy and environmental problems are increasingly prominent. As a carrier for storing electric energy, a lithium ion secondary battery has the advantages of high energy density, long cycle life, small self-discharge effect, environmental friendliness and the like, and is widely applied to the fields of mobile phones, digital portable products and the like at present. The electrolyte is an important component in lithium ion batteries and plays an important role in transporting ions. However, the safety problems of leakage, combustion and even explosion of the electrolyte of the conventional lithium ion battery frequently occur in recent years, and become a potential safety hazard.
Compared with the traditional liquid electrolyte, the solid electrolyte has the advantages of nonflammability, difficult volatilization, no leakage and the like, and can fundamentally solve the safety problem of the lithium ion battery; meanwhile, the solid electrolyte has a wider potential window, can replace electrolyte and a diaphragm at the same time, can obviously improve the working voltage of the battery, and improve the energy density of the battery; in addition, solid electrolytes also have higher thermal stability and mechanical strength, thus theoretically enabling batteries to operate under more severe environmental conditions and have longer cycle life; the above-mentioned advantages of solid electrolytes make solid lithium batteries of particular interest.
However, the major bottleneck of hindering the application of the solid electrolyte at present is the interface problem between the solid electrode and the solid electrolyte, and the transfer of lithium ions between the electrode and the electrolyte is hindered, which seriously affects the high rate performance, the cycle stability and the like of the battery.
Disclosure of Invention
In view of the above, the invention provides a lithium iron phosphate/gel electrolyte composite positive electrode material and a preparation method thereof, and a solid-state lithium battery and a preparation method thereof.
In order to achieve the above object, the present invention provides the following technical solutions:
the invention provides a lithium iron phosphate/gel electrolyte composite positive electrode material, which comprises a current collector and an active material composition on the surface of the current collector;
the active material composition comprises lithium iron phosphate powder, conductive carbon black and gel electrolyte coated on the surfaces of the lithium iron phosphate powder and the conductive carbon black;
the gel electrolyte contains polymerized polyethylene glycol diacrylate and a solidified lithium salt electrolyte.
Preferably, the mass ratio of the lithium iron phosphate powder to the conductive carbon black is (3-4): 1;
the molar ratio of lithium element in the solidified lithium salt electrolyte to-CCO-chain segment in the polymerized polyethylene glycol diacrylate is (7-9): 1;
the mass ratio of lithium salt to lithium iron phosphate powder in the solidified lithium salt electrolyte is 1 (8-70);
the coating amount of the active material composition on the surface of the current collector is 0.6-1.8 g/cm2。
The invention also provides a preparation method of the lithium iron phosphate/gel electrolyte composite cathode material, which comprises the following steps:
(1) mixing and homogenizing lithium iron phosphate powder, conductive carbon black, polyethylene glycol diacrylate, a photoinitiator, a lithium salt solution and a dispersing solvent to obtain homogeneous slurry;
(2) coating the homogeneous slurry obtained in the step (1) on the surface of a current collector to obtain a pole piece;
(3) and (3) carrying out ultraviolet curing on the pole piece obtained in the step (2) to obtain the lithium iron phosphate/gel electrolyte composite positive electrode material.
Preferably, the particle size of the lithium iron phosphate powder is 200-800 nm;
the relative molecular mass of the polyethylene glycol diacrylate is 400-1000;
the photoinitiator is 2-hydroxy-2-methyl-1-phenyl-1-acetone;
the dispersing solvent is anhydrous acetonitrile.
Preferably, the mass ratio of the lithium iron phosphate powder to the conductive carbon black is (3-4): 1;
the molar ratio of lithium ions in the lithium salt solution to-CCO-chain segments in the polyethylene glycol diacrylate is (7-9): 1;
the mass ratio of the lithium salt to the lithium iron phosphate powder in the lithium salt solution is 1 (8-70);
the mass of the photoinitiator is 1-5% of that of the polyethylene glycol diacrylate;
the mass ratio of the volume of the dispersing solvent to the lithium iron phosphate powder is (0.8-2) mL: 1g of the total weight of the composition.
Preferably, the lithium salt in the lithium salt solution is LiTFSI or LiClO4And LiPF6One or more of;
the solvent in the lithium salt solution comprises ethylene carbonate and an auxiliary solvent, wherein the auxiliary solvent is one or more of diethyl carbonate, dimethyl carbonate and polycarbonate.
Preferably, the coating amount applied in the step (2) is 0.6-1.8 g/cm based on the total mass of the lithium iron phosphate powder, the conductive carbon black, the polyethylene glycol diacrylate, the photoinitiator and the lithium salt solution in the homogeneous slurry2。
The invention provides a solid-state lithium battery, which comprises an anode, a cellulose membrane and a metallic lithium cathode which are sequentially arranged, wherein the anode is made of the lithium iron phosphate/gel electrolyte composite anode material prepared by the technical scheme or the lithium iron phosphate/gel electrolyte composite anode material prepared by the preparation method of the technical scheme;
the lithium ion battery comprises a positive electrode, a lithium metal cathode, a lithium salt solution and an electrolyte, wherein the electrolyte is contained between the positive electrode and the lithium metal cathode, and the electrolyte is a condensate of the electrolyte solution comprising polyethylene glycol diacrylate, an initiator and the lithium salt solution.
The invention also provides a preparation method of the solid-state lithium battery in the technical scheme, which comprises the following steps:
(I) the lithium iron phosphate/gel electrolyte composite positive electrode material prepared by the preparation method of the technical scheme or the lithium iron phosphate/gel electrolyte composite positive electrode material prepared by the preparation method of the technical scheme is used as a positive electrode, metal lithium is used as a negative electrode, and the positive electrode, the cellulose membrane and the metal lithium negative electrode are sequentially arranged to obtain a battery matrix;
(II) injecting the electrolyte solution between the anode of the battery matrix and the metal lithium cathode, and then packaging to obtain the button cell; the electrolyte solution comprises polyethylene glycol diacrylate, an initiator and a lithium salt solution;
and (III) heating the button cell obtained in the step (II) to obtain a solid lithium battery.
Preferably, the heating treatment temperature in the step (III) is 60-70 ℃, and the heating treatment time is 2-6 h.
The invention provides a lithium iron phosphate/gel electrolyte composite positive electrode material, which comprises a current collector and an active material composition on the surface of the current collector; the active material composition comprises lithium iron phosphate powder, conductive carbon black and a gel electrolyte wrapped on the surfaces of the lithium iron phosphate powder and the conductive carbon black, wherein the gel electrolyte contains polymerized polyethylene glycol diacrylate and a solidified lithium salt electrolyte. The lithium iron phosphate/gel electrolyte composite anode provided by the invention realizes that the electrolyte is uniformly coated on the surface of the lithium iron phosphate nano particles, thereby obviously increasing the contact area of the lithium iron phosphate/gel electrolyte composite anode, promoting the transfer and transmission of lithium ions and reducing the polarization and interface impedance of the electrode.
The invention also provides a preparation method of the lithium iron phosphate/gel electrolyte composite anode material, in the process of preparing the composite anode material, lithium iron phosphate powder, conductive carbon black, lithium salt solution and the like are coated on a current collector in the form of homogeneous slurry and then subjected to ultraviolet curing, so that the electrolyte is uniformly coated on the surfaces of lithium iron phosphate nano particles, the gel electrolyte uniformly coated on the surfaces of the lithium iron phosphate powder is realized, the combination of the anode material and the electrolyte at a molecular level is realized, the contact area between the electrolyte and the lithium iron phosphate is remarkably increased, the transfer and transmission of lithium ions are promoted, the polarization and interface impedance of electrodes are reduced, and the problem of poor transmission effect caused by poor flowability of the solid electrolyte and difficulty in permeating into pores of the anode is solved.
The results of the embodiment show that the rate performance of the solid lithium battery prepared from the lithium iron phosphate/gel electrolyte composite cathode material prepared by the invention is excellent, 87.3% of capacity of the solid lithium battery is still maintained after the solid lithium battery is cycled for 100 times, the coulombic efficiency is maintained to be more than 99.5%, and good cycling stability is shown.
In addition, the solid lithium battery is prepared by an in-situ curing method, so that the electrode is tightly contacted with the electrolyte layer, a sufficient lithium ion transmission channel is ensured, and the requirement of charging and discharging of the battery under a larger current density can be met.
Drawings
The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.
Fig. 1 is SEM images of different magnifications of the lithium iron phosphate/gel electrolyte composite positive electrode prepared in example 1;
fig. 2 is a TEM image of the lithium iron phosphate/gel electrolyte composite positive electrode obtained in example 1.
Fig. 3 is an SEM image of the interface between the lithium iron phosphate/gel electrolyte composite positive electrode and the gel electrolyte in the solid lithium battery obtained in example 1;
fig. 4 is a rate performance graph of the solid-state battery obtained in example 1;
fig. 5 is a graph showing the cycle characteristics at a current density of 1C of the solid-state battery obtained in example 1;
fig. 6 is an electrochemical impedance spectrum of the solid-state battery obtained in example 1 before and after cycling for various times.
Detailed Description
The invention provides a lithium iron phosphate/gel electrolyte composite positive electrode material, which comprises a current collector and an active material composition on the surface of the current collector;
the active material composition comprises lithium iron phosphate powder, conductive carbon black and gel electrolyte coated on the surfaces of the lithium iron phosphate powder and the conductive carbon black;
the gel electrolyte contains polymerized polyethylene glycol diacrylate and a solidified lithium salt electrolyte.
The lithium iron phosphate/gel electrolyte composite positive electrode material provided by the invention comprises a current collector and an active material composition on the surface of the current collector. In the present invention, the current collector is preferably an aluminum sheet current collector; the invention has no special requirement on the size of the aluminum sheet current collector, and the method is well known by the technical personnel in the field.
In the present invention, the active material composition is uniformly coated on the surface of the current collector; the coating amount of the active material composition on the surface of the current collector is preferably 0.6-1.8 g/cm2More preferably 0.6 to 1.8g/cm2. In the invention, the active material composition comprises lithium iron phosphate powder, conductive carbon black and gel electrolyte coated on the surfaces of the lithium iron phosphate powder and the conductive carbon black. In the present invention, the particle size of the lithium iron phosphate powder is preferably 200 to 800nm, and more preferably 400 to 600 nm. The lithium iron phosphate powder with the particle size can shorten the transmission path of ions and electronsThe transmission speed is improved, and the rate performance of the anode is further improved.
In the present invention, the mass ratio of the lithium iron phosphate powder to the conductive carbon black is preferably (3-4): 1, and more preferably (3.5-3.8): 1. the sources of the lithium iron phosphate powder and the conductive carbon black are not particularly required, and the sources are known by those skilled in the art.
In the invention, the gel electrolyte is wrapped on the surface of the lithium iron phosphate powder and the surface of the conductive carbon black. In the present invention, the gel electrolyte contains polymerized polyethylene glycol diacrylate and a cured lithium salt electrolyte; the gel electrolyte takes polymerized polyethylene glycol diacrylate as a molecular skeleton, and a lithium salt solution is solidified and then formed into the molecular skeleton by gel to provide a dispersion medium.
In the present invention, the solidified lithium salt electrolyte is a gel-like material obtained by directly solidifying a lithium salt solution. In the present invention, the solvent in the lithium salt solution for curing to obtain the cured lithium salt electrolyte preferably includes ethylene carbonate and an auxiliary solvent, the auxiliary solvent further being one or more of diethyl carbonate, dimethyl carbonate and polycarbonate; the volume ratio of the ethylene carbonate and the auxiliary solvent is preferably 1: 1. The source of the lithium salt and the solvent is not particularly required in the present invention, and those skilled in the art will be familiar with them. In the present invention, the molar concentration of lithium ions in the lithium salt solution is preferably 1 mol/L; the solvent is hardly volatilized during the curing process and is completely retained in the gel electrolyte. In the present invention, the lithium salt in the solidified lithium salt electrolyte is preferably LiTFSI or LiClO4And LiPF6One or more of (a). In the invention, the molar ratio of lithium element in the solidified lithium salt electrolyte to-CCO-chain segment in the polymerized polyethylene glycol diacrylate is preferably (7-9): 1, more preferably 8: 1; the mass ratio of lithium salt to lithium iron phosphate powder in the solidified lithium salt electrolyte is preferably 1 (8-70), and more preferably 1: (20-30).
The invention provides a preparation method of a lithium iron phosphate/gel electrolyte composite positive electrode material, which comprises the following steps:
(1) mixing and homogenizing lithium iron phosphate powder, conductive carbon black, polyethylene glycol diacrylate, a photoinitiator, a lithium salt solution and a dispersing solvent to obtain homogeneous slurry;
(2) coating the homogeneous slurry prepared in the step (1) on the surface of a current collector to obtain a pole piece;
(3) and (3) carrying out ultraviolet curing on the pole piece obtained in the step (2) to obtain the lithium iron phosphate/gel electrolyte composite positive electrode material.
According to the invention, lithium iron phosphate powder, conductive carbon black, polyethylene glycol diacrylate, a photoinitiator, a lithium salt solution and a dispersing solvent are mixed and homogenized to obtain homogeneous slurry.
In the present invention, the mass ratio of the lithium iron phosphate powder to the conductive carbon black is preferably (3-4): 1, and more preferably (3.2-3.5): 1. in the invention, the lithium iron phosphate powder and the conductive carbon black are the same as those in the composite material in the technical scheme, and are not described herein again.
In the present invention, the lithium salt in the lithium salt solution is preferably LiTFSI or LiClO4And LiPF6One or more of (a). In the present invention, the solvent in the lithium salt solution preferably includes ethylene carbonate and an auxiliary solvent, the auxiliary solvent further being one or more of diethyl carbonate, dimethyl carbonate and polycarbonate; the volume ratio of the ethylene carbonate and the auxiliary solvent is preferably 1: 1. The source of the lithium salt and the solvent is not particularly required in the present invention, and those skilled in the art will be familiar with them. In the present invention, the molar concentration of lithium ions in the lithium salt solution is preferably 1 mol/L. In the present invention, the lithium salt solution serves as a lithium ion electrolyte.
In the invention, the mass ratio of the lithium salt to the lithium iron phosphate powder in the lithium salt solution is preferably 1 (8-70), and more preferably 1: (20-30).
In the invention, the relative molecular mass of the polyethylene glycol diacrylate (PEGDA) is preferably 400-1000, more preferably 450-850, and even more preferably 500-600. In the present invention, the PEGDA functions to provide a cross-linked polymer network to promote the solidification of the lithium salt solution in the homogeneous slurry, and the-EO-segment (i.e., the-CCO-segment) of the PEGDA also functions to conduct lithium ions.
In the invention, the molar ratio of lithium ions in the lithium salt solution to-CCO-chain segments in the raw material polyethylene glycol diacrylate is preferably (7-9): 1, more preferably (7.5 to 8): 1.
in the present invention, the photoinitiator is preferably 2-hydroxy-2-methyl-1-phenyl-1-propanone; the mass of the photoinitiator is preferably 1 to 5 percent of that of the polyethylene glycol diacrylate, and more preferably 1.5 to 3 percent. In the invention, the photoinitiator plays a role in triggering the opening of the carbon-carbon double bond of the PEGDA under the irradiation of ultraviolet light to initiate the polymerization of the PEGDA to obtain the final gel electrolyte.
In the present invention, the dispersion solvent is preferably anhydrous acetonitrile; the mass ratio of the volume of the dispersion solvent to the lithium iron phosphate powder is preferably (0.8-2) mL: 1g, more preferably (0.9 to 1.2) mL: 1g of the total weight of the composition. In the invention, the dispersing solvent plays a role in dispersing the raw material of the positive electrode and reducing the viscosity of the slurry, so that the subsequent coating of the pole piece is facilitated, and the acetonitrile has high volatility and can be quickly volatilized in the processes of coating the pole piece and ultraviolet curing.
The invention has no special requirements on the mixing mode of the lithium iron phosphate powder, the conductive carbon black, the polyethylene glycol diacrylate, the photoinitiator, the lithium salt solution and the dispersing solvent, and the material liquid mixing mode which is well known by the technical personnel in the field can be adopted. In the present invention, the mixing is specifically carried out under stirring conditions.
After the homogeneous slurry is obtained, the homogeneous slurry is coated on the surface of the current collector to obtain the pole piece. In the present invention, the current collector is identical to the above-mentioned lithium iron phosphate/gel electrolyte composite positive electrode material technical scheme, and details are not repeated herein. In the invention, the coating amount of the coating is preferably 0.6-1.8 g/cm based on the total mass of the lithium iron phosphate powder, the conductive carbon black, the polyethylene glycol diacrylate, the photoinitiator and the lithium salt solution in the homogeneous slurry2More preferably 0.8 to 1.6g/cm2More preferably 1.0 to 1.2g/cm2. The inventionThere is no particular requirement on the specific embodiment of the coating, and the method of coating the slurry on the surface of the current collector, which is well known to those skilled in the art, can be adopted.
After coating, the pole piece is subjected to ultraviolet curing to obtain the lithium iron phosphate/gel electrolyte composite anode material. In the invention, the time for ultraviolet curing is preferably 10-30 min, more preferably 15-28 min, and still more preferably 20-25 min. In the invention, the ultraviolet curing is to perform a curing process on the pole piece under the irradiation of ultraviolet light. In the invention, all PEGDA generated in the ultraviolet curing is subjected to polymerization reaction to obtain a cross-linked network, so that the complete curing of the electrode is realized.
The invention volatilizes the dispersing solvent in the ultraviolet curing process, and simultaneously under the excitation of ultraviolet light, the photoinitiator triggers the double bond of PEGDA to open and carry out addition polymerization reaction to form the polymer skeleton of the gel electrolyte; the solvent in the lithium salt solution is stable in property and not easy to volatilize, and still remains on the surface of the current collector in the curing process, the lithium ion electrolyte is cured in a polymer framework to form a gel electrolyte, and is uniformly coated on the surface of the lithium iron phosphate nano particles and simultaneously coated on the surface of the conductive carbon black, so that the uniform coating of the gel electrolyte on the surface of the lithium iron phosphate powder is realized, and the combination of the anode material and the electrolyte at a molecular level is realized, thereby the contact area between the electrolyte and the lithium iron phosphate is remarkably increased, the transfer and transmission of lithium ions are promoted, and the polarization and interface impedance of the electrode are reduced.
In the invention, the ultraviolet curing is carried out to obtain a current collector, lithium iron phosphate powder coated on the surface of the current collector, conductive carbon black and gel electrolyte coated on the surfaces of the lithium iron phosphate powder and the conductive carbon black; the gel electrolyte contains polymerized polyethylene glycol diacrylate and a solidified lithium salt solution. In the present invention, the photoinitiator content is negligible.
In the invention, the preparation of the lithium iron phosphate/gel electrolyte composite anode material is preferably carried out under the protection of argon; the examples of the invention were carried out in particular in a glove box filled with argon.
In the invention, the lithium iron phosphate/gel electrolyte composite positive electrode material is used as a positive electrode of a solid-state lithium battery; after the ultraviolet light is cured, the curing material is preferably cut to obtain the solid-state lithium battery anode with the target size.
The invention provides a solid-state lithium battery, which comprises an anode, a cellulose membrane and a metallic lithium cathode which are sequentially arranged, wherein the anode is made of the lithium iron phosphate/gel electrolyte composite anode material prepared by the technical scheme or the lithium iron phosphate/gel electrolyte composite anode material prepared by the preparation method of the technical scheme; the lithium ion battery comprises a positive electrode, a lithium metal cathode, a lithium salt solution and an electrolyte, wherein the electrolyte is contained between the positive electrode and the lithium metal cathode, and the electrolyte is a condensate of the electrolyte solution comprising polyethylene glycol diacrylate, an initiator and the lithium salt solution.
The solid lithium battery provided by the invention comprises a positive electrode, a cellulose membrane and a metal lithium negative electrode which are sequentially arranged. In the invention, the material of the positive electrode is the lithium iron phosphate/gel electrolyte composite positive electrode material in the technical scheme. In the present invention, the negative electrode is preferably a metallic lithium plate. The invention has no special requirement on the sizes of the anode and the cathode, and the sizes of the anode and the cathode of the lithium metal battery which are well known by the technical personnel in the field can be adopted.
In the invention, the thickness of the cellulose membrane is preferably 30-40 μm; the density of the cellulose membrane is preferably 0.4-0.5 g/cm3The air resistance of the cellulose membrane is preferably 80-150 sec/100 ml. The source of the cellulose membrane is not particularly required in the present invention, and commercially available products known to those skilled in the art may be used. In the invention, the cellulose membrane plays a role in supporting the electrolyte between the anode and the lithium metal cathode, so that the electrolyte strength is improved; but also serves to block the positive electrode and the metallic lithium negative electrode.
In the invention, an electrolyte is contained between the positive electrode and the metallic lithium negative electrode; the electrolyte is positioned on two sides of the cellulose membrane and in pores of the cellulose membrane, and the electrolyte and the cellulose membrane are jointly present between the positive electrode and the lithium metal negative electrode.
The electrolyte is a condensate of an electrolyte solution comprising polyethylene glycol diacrylate, an initiator and a lithium salt solution; the electrolyte is further preferably obtained by solidifying the electrolyte solution at the temperature of 60-70 ℃ for 2-6 h. In the invention, the curing temperature is further preferably 65-68 ℃; the curing time is further preferably 3-5 h.
In the invention, the mass of the polyethylene glycol diacrylate in the electrolyte solution is preferably 5-20%, more preferably 6-18%, and even more preferably 7-15% of the total mass of the electrolyte solution.
In the present invention, the initiator is preferably Azobisisobutyronitrile (AIBN); the mass of the initiator is preferably 1 to 5% of that of the polyethylene glycol diacrylate, and more preferably 1.5 to 3.5%.
In the present invention, the lithium salt solution is selected within the range of the lithium salt solution in the preparation scheme of the lithium iron phosphate/gel electrolyte composite material, and details are not repeated herein.
The invention also provides a preparation method of the solid-state lithium battery, which comprises the following steps;
(I) the lithium iron phosphate/gel electrolyte composite positive electrode material or the lithium iron phosphate/gel electrolyte composite positive electrode material prepared by the preparation method in the technical scheme is used as a positive electrode, metal lithium is used as a negative electrode, and the positive electrode, the cellulose membrane and the metal lithium negative electrode are sequentially arranged to obtain a battery matrix;
(II) injecting the electrolyte solution between the anode of the battery matrix and the metal lithium cathode, and then packaging to obtain the button cell; the electrolyte solution comprises polyethylene glycol diacrylate, an initiator and a lithium salt solution;
and (III) heating the button cell obtained in the step (II) to obtain a solid lithium battery.
In the present invention, the preparation of the solid-state lithium battery is preferably performed under the protection of argon; the examples of the invention were carried out in particular in a glove box filled with argon.
According to the invention, the lithium iron phosphate/gel electrolyte composite anode material prepared by the preparation method of the technical scheme or the lithium iron phosphate/gel electrolyte composite anode material prepared by the preparation method of the technical scheme is used as an anode, and metal lithium is used as a cathode; and sequentially superposing the anode, the cellulose membrane and the metal lithium cathode to obtain the battery matrix. In the present invention, the negative electrode and the cellulose membrane are the same as those in the above-mentioned technical solution of the solid-state lithium battery, and are not described herein again.
The method has no special requirement on the specific implementation mode of the stacking arrangement process of the anode, the cellulose membrane and the metallic lithium cathode, and can be realized by adopting the stacking mode of the anode, the membrane and the cathode in the solid-state lithium battery, which is well known by the technical personnel in the field.
According to the invention, after the electrolyte solution is injected between the anode and the metallic lithium cathode of the battery matrix, the button cell is obtained by packaging. In the present invention, the electrolyte solution includes polyethylene glycol diacrylate, an initiator, and a lithium salt solution; the electrolyte solution is the same as the electrolyte solution in the above-mentioned technical solution of the solid-state lithium battery, and is not described herein again. When the electrolyte solution is injected between the anode and the metallic lithium cathode, the electrolyte solution can permeate into pores of the cellulose membrane and can flow out from two sides of the cellulose membrane to be in contact with the anode and the cathode. In the present invention, the injection manner is further preferably dropwise; and dropwise adding the electrolyte solution onto a cellulose membrane positioned between the anode and the lithium metal anode, wherein the electrolyte solution permeates into two sides of the cellulose membrane through pores of the cellulose membrane and is respectively contacted with the anode and the lithium metal anode.
According to the invention, the cellulose membrane is further preferably superposed on the anode, and then the metal lithium cathode is superposed after the electrolyte solution is dripped on the cellulose membrane.
In the invention, the injection amount of the electrolyte solution is preferably 120-160 muL, and more preferably 140-150 muL in a CR2025 button cell.
After the injection of the electrolyte solution is finished, the invention packages the cell matrix injected with the electrolyte solution to obtain the button cell. The present invention does not require special implementation of the package, as is well known to those skilled in the art.
After the button cell is obtained, the button cell is heated to obtain the solid lithium battery. In the invention, the temperature of the heating treatment is preferably 60-70 ℃, and more preferably 62-65 ℃; the time of the heat treatment is preferably 2 to 6 hours, more preferably 2.5 to 5 hours, and even more preferably 3 to 4 hours. In the heating treatment process, the electrolyte solution positioned between the positive electrode and the metal lithium negative electrode is solidified to obtain the solid lithium battery. In the examples of the present invention, the heat treatment is carried out in an oven.
The lithium iron phosphate/gel electrolyte composite positive electrode material and the preparation method thereof, and the solid-state lithium battery and the preparation method thereof provided by the present invention will be described in detail with reference to the following examples, but they should not be construed as limiting the scope of the present invention.
Example 1
Preparing a lithium iron phosphate/gel electrolyte composite anode:
(1) mixing and stirring lithium iron phosphate powder, conductive carbon black, polyethylene glycol diacrylate monomer (PEGDA), a photoinitiator and lithium ion electrolyte with anhydrous acetonitrile to obtain homogeneous slurry. Wherein the particle size of the lithium iron phosphate powder is 200-800 nm, and the mass ratio of the lithium iron phosphate powder to the conductive carbon black (Super P) is 3: 1; the relative molecular mass of PEGDA was 400;
1mol L of lithium ion electrolyte-1LiPF of6Electrolyte, wherein the solvent is a mixed solvent of Ethylene Carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 1: 1; the molar ratio of lithium ions in the lithium ion electrolyte to-CCO-chain segments in the PEGDA monomer is 7:1, and the mass ratio of lithium salts in the lithium ion electrolyte to lithium iron phosphate is 1: 8; 2-hydroxy-2-methyl-1-phenyl-1-acetone (HMPP) is adopted as the photoinitiator, the mass ratio of the photoinitiator to the PEGDA is 1%, and the volume ratio of anhydrous acetonitrile to the lithium iron phosphate powder is 0.8 mL: 1g of a compound;
(2) according to the total mass of the lithium iron phosphate powder, the conductive carbon black, the polyethylene glycol diacrylate, the photoinitiator and the lithium salt solution in the homogeneous slurry, the obtained homogeneous slurry is calculated according to 0.6g/cm2Uniformly coating the aluminum sheet current collector in proportion;
(3) and (3) placing the aluminum sheet current collector coated with the slurry under ultraviolet light for irradiating for 10 minutes to ensure the complete polymerization of PEGDA, and volatilizing the acetonitrile solvent to obtain the lithium iron phosphate/gel electrolyte composite cathode material.
Preparing a solid lithium battery:
(I) mixing and stirring PEGDA, an initiator and lithium ion electrolyte to obtain an electrolyte solution, wherein the mass fraction of the PEGDA in the electrolyte mixed solution is 5%, the initiator adopts Azobisisobutyronitrile (AIBN), and the mass of the initiator accounts for 1% of that of the PEGDA;
(II) sequentially superposing the obtained lithium iron phosphate/gel electrolyte composite anode, a cellulose membrane (NKK) and a metal lithium sheet, injecting 120 mu L of the electrolyte solution obtained in the step (I) between the anode and the cathode, and packaging to obtain the button cell, wherein the processes of pole piece superposition and cell packaging are carried out in a glove box filled with argon;
and (III) heating the button cell obtained in the step (II) in an oven at 60 ℃ for 2h to solidify the electrolyte solution to obtain the solid lithium battery.
SEM photographs of the lithium iron phosphate/gel electrolyte composite positive electrode obtained in this example at low magnification and at high magnification are shown in fig. 1(a) and (b), respectively. It can be seen from fig. 1 that a layer of electrolyte is uniformly wrapped on the surfaces of the lithium iron phosphate particles and the pores between the particles are filled, and the structure can greatly increase the contact area between the lithium iron phosphate and the electrolyte, so that the lithium iron phosphate and the electrolyte can perform rapid ion exchange.
The lithium iron phosphate/gel electrolyte composite positive electrode obtained in this example was subjected to TEM observation, and as a result, as shown in fig. 2, it was found that the electrolyte and the lithium iron phosphate particles were tightly bonded to each other.
When SEM observation is performed on the solid-state lithium battery obtained in this embodiment, fig. 3 is an interface SEM image of the lithium iron phosphate/gel electrolyte composite positive electrode and the gel electrolyte layer, it can be seen that the entire electrolyte layer is tightly attached to the lithium iron phosphate/gel electrolyte composite positive electrode, and an adequate lithium ion transmission channel between the electrode and the electrolyte is ensured.
And carrying out constant current charge and discharge tests on the prepared solid lithium battery, wherein the charge and discharge voltage interval is 4.0V-2.5V. FIG. 4 is a graph of rate performance of a solid state lithium battery having a capacity of 155.2mAh g at current densities of 0.1C, 0.2C, 0.5C, 1C, 2C and 5C, respectively-1、153.1mAh g-1、143.1mAh g-1、131.2mAh g-1、111.3mAh g-1And 72mAh g-1And excellent rate performance is shown.
Fig. 5 is a cycle performance diagram of the solid-state lithium battery at a current density of 1C, and it can be seen from fig. 5 that the solid-state lithium battery still has 87.3% of capacity retention after 100 cycles at a current density of 0.5C, and the coulombic efficiency is maintained above 99.5%, thus showing good cycle stability.
Fig. 6 is an electrochemical impedance spectrum of the solid-state lithium battery before, after 100 cycles, and after 200 cycles, and it can be seen from the diagram that the charge transfer impedances (interface impedances) of the battery are respectively 85 Ω, 114 Ω, and 153 Ω before, after 100 cycles, and after 200 cycles, and the interface impedance of the battery before the cycle is small, which indicates that the construction of the lithium iron phosphate/gel electrolyte composite positive electrode significantly reduces the interface resistance, improves the contact between the electrode and the electrolyte, and the interface impedance of the battery in the cycle process does not change greatly, which indicates that the solid-state lithium battery constructs a stable electrode/electrolyte interface and has excellent cycle stability.
Example 2
Preparing a lithium iron phosphate/gel electrolyte composite anode:
(1) mixing and stirring lithium iron phosphate powder, conductive carbon black, polyethylene glycol diacrylate monomer (PEGDA), a photoinitiator and lithium ion electrolyte with anhydrous acetonitrile to obtain homogeneous slurry. Wherein the particle size of the lithium iron phosphate powder is 200-800 nm, and the mass ratio of the lithium iron phosphate powder to the conductive carbon black (Super P) is 7: 2; the relative molecular mass of PEGDA was 600;
1mol L of lithium ion electrolyte-1LiClO of4Electrolyte, wherein the solvent is a mixed solvent of Ethylene Carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 1: 1; lithium ionThe molar ratio of lithium ions in the sub-electrolyte to-CCO-chain segments in the PEGDA monomer is 8:1, and the mass ratio of lithium salts in the lithium ion electrolyte to lithium iron phosphate is 1: 20; 2-hydroxy-2-methyl-1-phenyl-1-acetone (HMPP) is adopted as the photoinitiator, the mass ratio of the photoinitiator to the PEGDA is 1%, and the volume ratio of anhydrous acetonitrile to the lithium iron phosphate powder is 1.2 mL: 1g of a compound;
(2) according to the total mass of the lithium iron phosphate powder, the conductive carbon black, the polyethylene glycol diacrylate, the photoinitiator and the lithium salt solution in the homogeneous slurry, the obtained homogeneous slurry is calculated according to the mass of 1.2g/cm2Uniformly coating the aluminum sheet current collector in proportion;
(3) and (3) placing the aluminum sheet current collector coated with the slurry under ultraviolet light for irradiating for 20 minutes to ensure the complete polymerization of PEGDA, and volatilizing the acetonitrile solvent to obtain the lithium iron phosphate/gel electrolyte composite cathode material.
Preparing a solid lithium battery:
(I) mixing and stirring PEGDA, an initiator and lithium ion electrolyte to obtain an electrolyte solution, wherein the mass fraction of the PEGDA in the electrolyte mixed solution is 10%, the initiator adopts Azobisisobutyronitrile (AIBN), and the mass of the initiator accounts for 2% of that of the PEGDA;
(II) sequentially superposing the obtained lithium iron phosphate/gel electrolyte composite anode, a cellulose membrane (NKK) and a metal lithium sheet, injecting 140 mu L of the electrolyte solution obtained in the step (I) between the anode and the cathode, and packaging to obtain the button cell, wherein the processes of pole piece superposition and cell packaging are carried out in a glove box filled with argon;
and (III) heating the button cell obtained in the step (II) in an oven at 65 ℃ for 4h to solidify the electrolyte solution to obtain the solid lithium battery.
The solid lithium battery obtained in the embodiment is subjected to constant current charge and discharge tests, and the charge and discharge voltage interval is 4.0V-2.5V. The specific capacities of the solid lithium batteries at current densities of 0.1C, 0.2C, 0.5C, 1C, 2C and 5C are 153.7mAh g respectively-1、151.8mAh g-1、141.6mAhg-1、130.9mAh g-1、110.1mAh g-1And 69.3mAh g-1And excellent rate performance is shown.
The solid-state lithium battery is subjected to a cycle-specific capacity test, so that the solid-state lithium battery still has 86.5% of capacity maintenance after 100 cycles under the current density of 0.5C, the coulombic efficiency is maintained above 99.5%, and good cycle stability is shown.
Electrochemical impedance tests are carried out on the solid-state lithium battery under different cycle times, the charge transfer impedance (interface impedance) of the solid-state lithium battery is respectively 87 omega, 121 omega and 167 omega before, after 100 and 200 cycles, and the interface impedance of the battery before the cycle is smaller, so that the construction of the lithium iron phosphate/gel electrolyte composite anode obviously reduces the interface resistance, improves the contact between an electrode and an electrolyte, and the interface impedance of the battery in the cycle process is not changed greatly, so that the solid-state lithium battery constructs a stable electrode/electrolyte interface and has excellent cycle stability.
Example 3
Preparing a lithium iron phosphate/gel electrolyte composite anode:
(1) mixing and stirring lithium iron phosphate powder, conductive carbon black, polyethylene glycol diacrylate monomer (PEGDA), a photoinitiator and lithium ion electrolyte with anhydrous acetonitrile to obtain homogeneous slurry. Wherein the particle size of the lithium iron phosphate powder is 200-800 nm, and the mass ratio of the lithium iron phosphate powder to the conductive carbon black (Super P) is 4: 1; the relative molecular mass of PEGDA is 1000;
1mol L of lithium ion electrolyte-1The solvent is a mixed solvent of Ethylene Carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 1: 1; the molar ratio of lithium ions in the lithium ion electrolyte to-CCO-chain segments in the PEGDA monomer is 9:1, and the mass ratio of lithium salts in the lithium ion electrolyte to lithium iron phosphate is 1: 70; 2-hydroxy-2-methyl-1-phenyl-1-acetone (HMPP) is adopted as the photoinitiator, the mass ratio of the photoinitiator to PEGDA is 5%, and the volume ratio of anhydrous acetonitrile to lithium iron phosphate powder is 2 mL: 1g of a compound;
(2) according to the total mass of the lithium iron phosphate powder, the conductive carbon black, the polyethylene glycol diacrylate, the photoinitiator and the lithium salt solution in the homogeneous slurry, the obtained homogeneous slurry is calculated according to the mass of 1.8g/cm2Uniformly coating the aluminum sheet current collector in proportion;
(3) and (3) placing the aluminum sheet current collector coated with the slurry under ultraviolet light for irradiating for 30 minutes to ensure the complete polymerization of PEGDA, and volatilizing the acetonitrile solvent to obtain the lithium iron phosphate/gel electrolyte composite cathode material.
Preparing a solid lithium battery:
(I) mixing and stirring PEGDA, an initiator and lithium ion electrolyte to obtain an electrolyte solution, wherein the mass fraction of the PEGDA in the electrolyte mixed solution is 20%, the initiator adopts Azobisisobutyronitrile (AIBN), and the mass of the initiator accounts for 5% of that of the PEGDA;
(II) sequentially superposing the obtained lithium iron phosphate/gel electrolyte composite positive electrode, a cellulose membrane (NKK) and a metal lithium sheet, injecting 160 mu L of the electrolyte solution obtained in the step (I) between the positive electrode and the negative electrode, and packaging to obtain the button cell, wherein the processes of superposing the electrode sheets and packaging the cell are carried out in a glove box filled with argon;
and (III) heating the button cell obtained in the step (II) in an oven at 70 ℃ for 6h to solidify the electrolyte solution to obtain the solid lithium battery.
The solid lithium battery obtained in the embodiment is subjected to constant current charge and discharge tests, and the charge and discharge voltage interval is 4.0V-2.5V. The specific capacities of the solid lithium batteries at current densities of 0.1C, 0.2C, 0.5C, 1C, 2C and 5C are 153.2mAh g respectively-1、150.9mAh g-1、140.4mAh g-1、127.1mAh g-1、106.5mAh g-1And 65.7mAh g-1And excellent rate performance is shown.
The solid lithium battery is subjected to a cycle-specific capacity test, and the result shows that the solid lithium battery still has 83.4% of capacity retention after 100 cycles under the current density of 0.5C, the coulomb efficiency is maintained above 99.5%, and good cycle stability is shown.
Electrochemical impedance tests are carried out on the solid-state lithium battery under different cycle times, the charge transfer impedance (interface impedance) of the solid-state lithium battery is respectively 89 omega, 125 omega and 173 omega before cycle, after 100 cycles and 200 cycles, and the interface impedance of the battery before cycle is small, so that the construction of the lithium iron phosphate/gel electrolyte composite positive electrode obviously reduces the interface resistance, improves the contact between the electrode and the electrolyte, and the interface impedance of the battery in the cycle process is not changed greatly, so that the solid-state lithium battery constructs a stable electrode/electrolyte interface and has excellent cycle stability.
The results of the above examples show that the method provided by the invention is simple, and the lithium iron phosphate/gel electrolyte composite anode can be prepared by a one-step ultraviolet curing method; the solid-state lithium battery can be prepared by an in-situ curing method, the preparation method is simple and controllable, and the coating technology can be combined with the coating technology of modern commercial lithium ion battery production, so that the large-scale production and industrialization are facilitated.
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 (10)

1. A lithium iron phosphate/gel electrolyte composite positive electrode material comprises a current collector and an active material composition coated on the surface of the current collector;
the active material composition comprises lithium iron phosphate powder, conductive carbon black and gel electrolyte coated on the surfaces of the lithium iron phosphate powder and the conductive carbon black;
the gel electrolyte contains polymerized polyethylene glycol diacrylate and solidified lithium salt electrolyte;
the molar ratio of lithium element in the solidified lithium salt electrolyte to-CCO-chain segment in the polymerized polyethylene glycol diacrylate is (7-9): 1;
the mass ratio of lithium salt to lithium iron phosphate powder in the solidified lithium salt electrolyte is 1: (8-70);
the preparation method of the lithium iron phosphate/gel electrolyte composite anode material comprises the following steps:
(1) mixing and homogenizing lithium iron phosphate powder, conductive carbon black, polyethylene glycol diacrylate, a photoinitiator, a lithium salt solution and a dispersing solvent to obtain homogeneous slurry;
(2) coating the homogeneous slurry obtained in the step (1) on the surface of a current collector to obtain a pole piece;
(3) and (3) carrying out ultraviolet curing on the pole piece obtained in the step (2) to obtain the lithium iron phosphate/gel electrolyte composite positive electrode material.
2. The lithium iron phosphate/gel electrolyte composite positive electrode material according to claim 1, wherein the mass ratio of the lithium iron phosphate powder to the conductive carbon black is preferably (3-4): 1;
the coating amount of the active material composition on the surface of the current collector is 0.6-1.8 g/cm2。
3. A preparation method of a lithium iron phosphate/gel electrolyte composite anode material comprises the following steps:
(1) mixing and homogenizing lithium iron phosphate powder, conductive carbon black, polyethylene glycol diacrylate, a photoinitiator, a lithium salt solution and a dispersing solvent to obtain homogeneous slurry;
(2) coating the homogeneous slurry obtained in the step (1) on the surface of a current collector to obtain a pole piece;
(3) and (3) carrying out ultraviolet curing on the pole piece obtained in the step (2) to obtain the lithium iron phosphate/gel electrolyte composite positive electrode material.
4. The preparation method according to claim 3, wherein the particle size of the lithium iron phosphate powder is 200 to 800 nm;
the relative molecular mass of the polyethylene glycol diacrylate is 400-1000;
the photoinitiator is 2-hydroxy-2-methyl-1-phenyl-1-acetone;
the dispersing solvent is anhydrous acetonitrile.
5. The preparation method according to claim 3 or 4, wherein the mass ratio of the lithium iron phosphate powder to the conductive carbon black is (3-4): 1;
the molar ratio of lithium ions in the lithium salt solution to-CCO-chain segments in the polyethylene glycol diacrylate is (7-9): 1;
the mass ratio of lithium salt to lithium iron phosphate powder in the lithium salt solution is 1: (8-70);
the mass of the photoinitiator is 1-5% of that of the polyethylene glycol diacrylate;
the mass ratio of the volume of the dispersion solvent to the lithium iron phosphate powder is (0.8-2) mL: 1g of the total weight of the composition.
6. The method according to claim 3, wherein the lithium salt in the lithium salt solution is LiTFSI or LiClO4And LiPF6One or more of;
the solvent in the lithium salt solution comprises ethylene carbonate and an auxiliary solvent, wherein the auxiliary solvent is one or more of diethyl carbonate, dimethyl carbonate and polycarbonate.
7. The method according to claim 3, wherein the coating amount applied in the step (2) is 0.6 to 1.8g/cm based on the total mass of the lithium iron phosphate powder, the conductive carbon black, the polyethylene glycol diacrylate, the photoinitiator and the lithium salt solution in the homogeneous slurry2。
8. A solid-state lithium battery comprises a positive electrode, a cellulose membrane and a lithium metal negative electrode which are sequentially arranged, wherein the material of the positive electrode is the lithium iron phosphate/gel electrolyte composite positive electrode material according to any one of claims 1 to 2 or the lithium iron phosphate/gel electrolyte composite positive electrode material prepared by the preparation method according to any one of claims 3 to 7;
the lithium ion battery comprises a positive electrode, a lithium metal cathode, a lithium salt solution and an electrolyte, wherein the electrolyte is contained between the positive electrode and the lithium metal cathode, and the electrolyte is a condensate of the electrolyte solution comprising polyethylene glycol diacrylate, an initiator and the lithium salt solution.
9. A method of manufacturing a solid state lithium battery as claimed in claim 8, comprising the steps of:
(I) the lithium iron phosphate/gel electrolyte composite positive electrode material according to any one of claims 1 to 2 or the lithium iron phosphate/gel electrolyte composite positive electrode material prepared by the preparation method according to any one of claims 3 to 7 is used as a positive electrode, metal lithium is used as a negative electrode, and the positive electrode, the cellulose membrane and the metal lithium negative electrode are sequentially arranged to obtain a battery matrix;
(II) injecting the electrolyte solution between the anode of the battery matrix and the metal lithium cathode, and then packaging to obtain the button cell; the electrolyte solution comprises polyethylene glycol diacrylate, an initiator and a lithium salt solution;
and (III) heating the button cell obtained in the step (II) to obtain a solid lithium battery.
10. The method according to claim 9, wherein the heating treatment in step (III) is carried out at a temperature of 60 to 70 ℃ for 2 to 6 hours.
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