Semi-solid electrolyte for lithium metal battery and preparation method of semi-solid electrolyte

Abstract

The invention discloses a semi-solid electrolyte for a lithium metal battery and a preparation method of the semi-solid electrolyte, and the semi-solid electrolyte is prepared by taking polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) as a matrix, ethylene glycol dimethacrylate (EGDMA) as a monomer, N-isopropylacrylamide (NIPAM) as a cross-linking agent and azodiisobutyronitrile (AIBN) as an initiator through heating in an in-situ polymerization mode to initiate thermal polymerization. The material with good thermal stability, high-temperature working applicability and cycle reversibility is obtained, the material serves as a semi-solid electrolyte of a lithium metal battery, and under the conditions that the high temperature is 60 DEG C and the current density is 1C, a battery with lithium iron phosphate as a positive electrode circulates for 400 circles and keeps 90% of capacity; under the condition that the high temperature is 60 DEG C and the current density is 1C, the battery taking the lithium cobalt oxide as the positive electrode can circulate for 550 circles. The preparation method is simple, can be suitable for working at high temperature, and is suitable for batch production.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium batteries, and specifically relates to a semi-solid electrolyte for lithium metal batteries and a preparation method thereof. The semi-solid electrolyte can be used for lithium metal batteries in high-temperature environments. Background Art

[0002] In industrial applications, high temperature conditions (such as above 50°C) are common working environments, and how to achieve stable operation of lithium metal batteries (LMBs) at high temperatures, improve energy density and extend cycle life has become a hot topic of current research. To meet the above challenges, gel polymer electrolytes (GPEs) have attracted widespread attention due to their excellent mechanical strength, thermal stability and interfacial compatibility. However, conventional GPEs still face problems such as softening of polymer segments, decreased ionic conductivity and intensified side reactions at the electrode / electrolyte interface at high temperatures. For example, a single polymer matrix fails to contact the interface due to thermal shrinkage at high temperatures (>60°C), and the local concentration gradient of the electrolyte triggers uneven deposition of lithium.

[0003] In recent years, in-situ polymerization gel electrolyte technology has provided a new approach to solving the problem of high-temperature adaptability. This technology forms a three-dimensional network structure by directly polymerizing monomers inside the battery, which can achieve close fit between the electrolyte and the electrode, reduce interfacial impedance and improve thermal stability. Polymer electrolytes can also inhibit the cross-talk effect of heat-induced gas species during thermal runaway. In addition, the thermal response characteristics exhibited by some polymer electrolytes (the battery is thermally shut down before reaching the thermal runaway temperature) significantly improve the thermal safety of lithium batteries. For example, Liu et al. developed an in-situ polymerized flame-retardant gel electrolyte (FRGE) for high-performance and safe LMBs. This electrolyte combines the excellent flame retardancy of phosphates with high ionic conductivity. At the same time, the introduction of its polymer skeleton effectively inhibits the growth of lithium dendrites, thereby improving the cycle stability and safety of the battery (Nano Energy, 2021, 91, 106679). Zhen et al. designed a new electrolyte by in situ polymerization of 1,3-dioxolane (DOL) solvent on a high-temperature resistant liquid electrolyte, which significantly improved the performance of LMB at 80°C (Batteries-Basel, 2023, 9, 9010028). Ma et al. used polyethylene glycol methyl ether acrylate (PEGMEA) as a monomer, added polyethylene glycol (PEG) lithium salt and carbonate electrolyte, and obtained GPEs with good chemical stability and high ionic conductivity at high temperature by in situ polymerization. There was no capacity decay after 150 cycles at 60°C and 0.5C. In addition, the battery showed 160.3mAh g -1The high initial reversible capacity of GPEs was achieved at a high temperature of 0.5°C and 80°C, providing 100 stable cycles (Small, 2025, 21, 2412259). However, these studies directly formed a three-dimensional network structure inside the battery, making it difficult to determine the uniformity of the gel electrolyte formed between the electrodes. The uneven electrolyte interface will affect the migration of lithium ions and ionic conductivity in LMBs. In addition, these studies improved the thermal stability of GPEs by dissolving some additives or flame retardants. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a semi-solid electrolyte for lithium metal batteries and a preparation method thereof in view of the existing technology. The technical process is simple and suitable for large-scale production.

[0005] The technical solution adopted by the present invention to solve the above technical problems is: preparing the gel electrolyte by in-situ polymerization, which specifically includes the following steps:

[0006] 1) Add an appropriate amount of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) polymer to N-methylpyrrolidone (NMP) solvent, then heat and stir at 60°C until completely dissolved to obtain a white, transparent, viscous solution. Then, use a dropper to drop this liquid onto aluminum foil, spread it evenly with a blade, and immerse it in dispersant water;

[0007] 2) After standing for a period of time, the gel phase turns into a gel state. The gel is then peeled off the aluminum foil, dried at 50°C for 8 hours, and cut into membrane-sized pieces (19 mm in diameter) for later use.

[0008] 3) The monomer ethylene glycol dimethacrylate (EGDMA) and the crosslinker N-isopropylacrylamide (NIPAM) were added in a 1:1 mass ratio to a commercial electrolyte (1M lithium hexafluorophosphate (LiPF6), ethylene carbonate (EC): diethyl carbonate (DEC) = 1:1 volume ratio, containing 5% fluoroethylene carbonate (FEC)). The combined mass fraction of the monomer and crosslinker was 10%. 0.5 wt% azobisisobutyronitrile (AIBN) was then added and stirred uniformly with a magnetic stirrer to obtain a precursor solution. When assembling a button cell, the precursor solution was added to a PVDF-HFP separator and allowed to fully absorb. After assembly, the cell was allowed to stand for a period of time. The cell was then placed in a 60°C vacuum oven for 2 hours to initiate in-situ polymerization to form a gel electrolyte suitable for high-temperature operation in lithium metal batteries. This is the aforementioned semi-solid electrolyte for lithium metal batteries.

[0009] Furthermore, the present invention also provides the use of the semi-solid electrolyte. The electrolyte material is used as a semi-solid electrolyte in lithium metal batteries for stable cycling at high temperatures. Under high temperature of 60°C and current conditions of 1C, the battery with lithium iron phosphate as the positive electrode can maintain 90% of its capacity after 400 cycles, and the battery with lithium cobalt oxide as the positive electrode can be cycled 550 cycles; the assembled lithium copper battery can maintain 90% of its capacity after 400 cycles at 0.5 mA cm -2 After charging and discharging for 1 hour and 100 cycles at a current density of , the average coulombic efficiency can reach 94.7%.

[0010] Compared with the prior art, the present invention has the following characteristics:

[0011] The electrolyte described in the present invention is an in-situ polymerized gel electrolyte, whose polymer matrix has uniform pores of 1 μm and a three-dimensional network structure. A precursor solution formed by mixing EGDMA, NIPAM, AIBN and a commercial electrolyte is uniformly filled in the pores of the matrix, and thermal induction forms a uniform and stable gel electrolyte (PEN), and the electrode and electrolyte interface are in close contact. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 TG curve of the semi-solid electrolyte prepared in Example 1 of the present invention;

[0013] Figure 2 This is the SEM morphology of the semi-solid electrolyte prepared in Example 1 of the present invention;

[0014] Figure 3 The semi-solid electrolyte prepared in Example 1 of the present invention was used in lithium-copper batteries. -2 Coulombic efficiency diagram of 100 cycles at a current density of ;

[0015] Figure 4 The semi-solid electrolyte prepared in Example 1 of the present invention is used in a lithium metal battery (lithium iron phosphate positive electrode) at a high temperature of 60°C and a current density of 1C, and the discharge specific capacity and coulombic efficiency are shown.

[0016] Figure 5 The semi-solid electrolyte prepared in Example 1 of the present invention is used in a lithium metal battery (lithium cobalt oxide positive electrode) at a high temperature of 60°C and a current density of 1C, and the discharge specific capacity and coulombic efficiency are shown. DETAILED DESCRIPTION

[0017] The present invention is described in further detail below with reference to the examples.

[0018] Example 1

[0019] 1.0g of PVDF-HFP was weighed and added to 4.0g of NMP. The mixture was heated and stirred at 60°C until completely dissolved, yielding a white, transparent, viscous solution. This solution was then dripped onto aluminum foil with a dropper, spread evenly with a blade, and immersed in dispersant water. After standing for a period of time, the solution transformed into a gel. The gel was then peeled from the foil, dried at 50°C for 8h, and cut into separator-sized pieces (19mm diameter) for later use. 0.3g each of the monomer EGDMA and the crosslinker NIPAM were weighed and added to 5.4g of a commercial electrolyte (1M LiPF6, EC:DEC = 1:1, containing 5% FEC). 0.015g of AIBN was then added and stirred evenly with a magnetic stirrer to yield a precursor solution. When assembling a lithium metal battery, the precursor solution is added to the PVDF-HFP diaphragm to allow it to be fully absorbed. After assembly, the battery is allowed to stand for a period of time, and then placed in a 60°C vacuum oven for thermal induction for 2 hours to form an in-situ polymerization gel electrolyte for lithium metal batteries working at high temperatures, which is the semi-solid electrolyte for lithium metal batteries.

[0020] The obtained semi-solid electrolyte was subjected to thermogravimetric (TG) test to obtain the composition structure of the electrolyte ( Figure 1 ); The morphology of the gel electrolyte was observed using a scanning electron microscope (SEM), and a three-dimensional network structure with filled pores was obtained ( Figure 2 ); The gel electrolyte was used in lithium copper batteries and its -2 The average Coulombic efficiency after 100 cycles at a current density of 94.7% ( Figure 3 ); Under the condition of high temperature 60℃ and current density 1C, the battery with lithium iron phosphate as the positive electrode maintains 90% of its capacity after 400 cycles ( Figure 4 ); Under the condition of high temperature 60℃ and current density 1C, the battery with lithium cobalt oxide as the positive electrode can cycle 550 times ( Figure 5 ).

[0021] Example 2

[0022] 1.0g of PVDF-HFP was weighed and added to 4.0g of NMP. The mixture was heated and stirred at 60°C until completely dissolved, yielding a white, transparent, viscous solution. This solution was then dripped onto aluminum foil with a dropper, spread evenly with a blade, and immersed in dispersant water. After standing for a period of time, the solution transformed into a gel. The gel was then peeled from the foil, dried at 50°C for 8h, and cut into separator-sized pieces (19mm diameter) for later use. 0.3g each of the monomer EGDMA and the crosslinker NIPAM were weighed and added to 5.4g of a commercial electrolyte (1M LiPF6, EC:DEC = 1:1, containing 5% FEC). 0.015g of AIBN was then added and stirred evenly with a magnetic stirrer to yield a precursor solution. When assembling a lithium metal battery, the precursor solution is added to the PVDF-HFP diaphragm to allow it to be fully absorbed. After assembly, the battery is allowed to stand for a period of time, and then placed in a 60°C vacuum oven for thermal induction for 2 hours to form an in-situ polymerization gel electrolyte for lithium metal batteries working at high temperatures, which is the semi-solid electrolyte for lithium metal batteries.

[0023] The obtained semi-solid electrolyte was subjected to thermogravimetric analysis to obtain the thermal stability of the material. The morphology of the material was observed using a scanning electron microscope (SEM), which revealed a three-dimensional network structure with pores filled with gel electrolyte. The material was used in lithium-copper batteries and the performance was evaluated at 0.5 mAh cm -2 The coulombic efficiency was tested at a current density of ; it was used in lithium iron phosphate (lithium cobalt oxide) positive electrode batteries, and its cycle performance was tested at a high temperature of 60°C and a current density of 1C.

Claims

1. A method for preparing a semi-solid electrolyte for lithium metal batteries, characterized in that: The preparation method comprises the following steps: 1) Add an appropriate amount of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) polymer to NMP solvent, then heat and stir at 60°C until completely dissolved to obtain a white, transparent, viscous solution. Then, use a dropper to drop this liquid onto aluminum foil, apply it evenly with a blade, and immerse it in dispersant water; 2) After standing for a period of time, the gel phase turns into a gel state; the gel is then peeled off the aluminum foil, dried at 50°C for 8 hours, and cut into the size of a diaphragm with a diameter of 19 mm for later use; 3) The monomer EGDMA and the cross-linker NIPAM are added to a commercial electrolyte in a mass ratio of 1:1 to obtain a mixed solution; the commercial electrolyte includes 1M LiPF6, EC:DEC=1:1, and contains 5% FEC; the sum of the mass fractions of the monomer and the cross-linker in the mixed solution is 10%, and then 0.5wt% AIBN is added, and the mixture is stirred evenly with a magnetic stirrer to obtain a precursor solution; when assembling a lithium metal battery, the precursor solution is added to the PVDF-HFP membrane to allow it to be fully absorbed. After the assembly is completed, the precursor solution is allowed to stand for a period of time, and the battery is placed in a vacuum oven at 60°C for 2 hours to initiate in-situ polymerization to form a gel electrolyte for lithium metal batteries operating at high temperatures, which is the semi-solid electrolyte for lithium metal batteries.

2. A semi-solid electrolyte for lithium metal batteries prepared by the preparation method according to claim 1.

3. A semi-solid electrolyte for lithium metal batteries according to claim 2, characterized in that: This semi-solid electrolyte is used in lithium metal batteries and has a high efficiency of 0.5 mAh cm in lithium copper batteries. -2 The average coulombic efficiency is 94.7% after 100 cycles at a current density of 1C; at a high temperature of 60°C and a current density of 1C, the battery with lithium iron phosphate as the positive electrode maintains 90% of its capacity after 400 cycles; at a high temperature of 60°C and a current density of 1C, the battery with lithium cobalt oxide as the positive electrode can cycle 550 cycles.

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