A method for preparing an in situ gel

Abstract

The application discloses a kind of in-situ gel preparation methods, belong to lithium metal battery technical field.The method introduces trace initiator to make 1,3-dioxolane DOL in electrolyte occur ring-opening polymerization reaction, by forming DOL crosslinking in advance, realize liquid ether-based electrolyte in-situ solidification on the surface of lithium negative electrode.After forming gel phase, inject electrolyte in soft pack battery of gel phase, construct gel phase@liquid phase two-phase system.By controlling the ratio of electrolyte and poly-DOL, realize the gradient solidification of ether-based electrolyte in battery, adjust the mechanical properties of gel electrolyte.There is intermolecular interaction between poly-DOL and lithium salt anion, significantly improve the ionic conductivity and lithium ion transference number of gel electrolyte, the in-situ gel phase formed has good interface compatibility with lithium negative electrode, and the growth of lithium dendrite is inhibited.This in-situ gel preparation method is low in cost and easy to operate, and is a simple method to realize high capacity and high cycle stability of lithium metal battery.

Description

TECHNICAL FIELD

[0001] The application discloses a preparation method of in-situ gel, and belongs to the field of lithium metal batteries. BACKGROUND

[0002] Metal lithium is considered as the first choice of negative electrode materials in high specific energy batteries due to its lowest chemical potential (-3.04V vs S.H.E.) and extremely high theoretical specific capacity (3860mAh / g). However, metal lithium negative electrode is prone to accumulate at the interface defects in the electrochemical reaction of liquid lithium battery, forming a non-uniform internal micro-electric field, resulting in a concentration gradient, and finally inducing dendrite growth and electrode pulverization and other interface problems. In recent years, researchers have tried to use solid-state electrolyte, artificial SEI film construction, functional coating and other strategies to inhibit the growth of lithium dendrites. Among them, gel polymer electrolyte (GPE) is particularly popular due to its better stability than traditional liquid electrolyte for lithium negative electrode. However, in soft package batteries, the application of gel electrolyte has the following problems: (1) the physical contact between the electrode / electrolyte interface is poor, and the volume expansion / contraction of the electrode material occurs during the cycle process, the electrode will lose contact with the gel electrolyte and cause delamination, resulting in uneven contact and causing electrochemical failure problems. (2) There are side reactions between the electrode material and the gel electrolyte interface, especially when the voltage or temperature is increased during the test process, the side reaction process will be more significant. Therefore, the ideal gel electrolyte in lithium metal batteries should have good interface contact and interface stability under full life cycle conditions.

[0003] In order to solve the above problems, in-situ polymerization to form a gel polymer electrolyte is an effective method to construct a good compatible interface. Most of the research on gel electrolyte focuses on the modification of the electrolyte itself, for example, CN 114207902A discloses an electrolyte containing a carbonate compound as an additive, and CN 114142081A discloses a gel electrolyte formed by sulfonating and cross-linking a polyether ether ketone polymer matrix. SUMMARY

[0004] The purpose of the present application is to solve the problems existing in the preparation of gel electrolyte and its application in lithium metal batteries, and to provide a preparation method of in-situ gel. The in-situ gel method solves the interface compatibility and contact problem between the gel electrolyte and the electrode material, and the gel phase has the ability to store liquid, which locks different proportions of ether-based organic matter with good fluidity in the gel phase. Through the stress induction of the lithium negative electrode during the cycle process, the physical contact of the interface during the cycle process is ensured, and the cycle and electrochemical performance of the battery is increased.

[0005] The technical scheme adopted by the present application to solve the above problems is as follows: a preparation method of in-situ gel, the steps are as follows:

[0006] Dissolve the lithium salt in a solvent mixed by 1,3-dioxolane DOL and ether organic matter, stir at room temperature under argon atmosphere at 100-200 rpm for 24 hours to make the lithium salt completely dissolved; then, dissolve the initiator in the electrolyte, stir under argon atmosphere at 100-200 rpm for 0.5-24 hours, inject into the battery, stand at room temperature for 12-24 hours, and then add 1-10 ml of electrolyte without initiator;

[0007] The lithium salt is one or more of lithium bis(trifluoromethanesulfonyl)imide LiTFSI, lithium bis(fluorosulfonyl)imide LiFSI, lithium hexafluorophosphate LiPF6, lithium nitrate LiNO3, and lithium tetrafluoroborate LiBF4, and the total concentration of the lithium salt is 0.1-5 M;

[0008] The linear ether organic matter is one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether; and the volume ratio of 1,3-dioxolane DOL to the linear ether organic matter is 9:1-3:7;

[0009] The initiator is a Lewis acid, which is one or more of aluminum chloride, iron chloride, boron trifluoride, and niobium pentachloride, and the amount is 0.1-10 mM;

[0010] The electrolyte without initiator is one or more of ether electrolyte and carbonate electrolyte;

[0011] The ether electrolyte is one or more of tetrahydrofuran THF, 2-methyltetrahydrofuran 2me-thf, 1,3-dioxolane DOL, dimethoxymethane DMM, 1,2-dimethoxyethane DME, and diethylene glycol dimethyl ether DG;

[0012] The carbonate electrolyte is one or more of propylene carbonate PC, ethylene carbonate EC, methyl ethyl carbonate EMC, diethyl carbonate DEC, dimethyl carbonate DMC, methyl acrylate MA, and ethyl acrylate EA.

[0013] The lithium negative electrode is metal lithium or lithium alloy.

[0014] The present application has the following beneficial effects: (1) the initiator is used to initiate the polymerization reaction on the electrode / electrolyte interface, and a gel polymer electrolyte layer is generated in situ on the surface of the lithium negative electrode, and the interface compatibility is improved;

[0015] (2) the biphasic system contains ether-based organic matter with good fluidity, which can self-adjust the physical contact performance of the interface during the cycle process, and inhibit the side reaction of the lithium negative electrode;

[0016] (3) ether organic matter and DOL polymer interact, reduce the degree of space crowded reactants, the increased O-containing group also provides a relatively loose binding site for lithium ions, the gel electrolyte ion conductance is improved, the ion migration ability is enhanced. The method improves the interface compatibility and interface contact problem between the gel electrolyte and the lithium negative electrode, by adjusting the ratio and type of gel phase and flow phase in the gel electrolyte, an in-situ gel electrolyte with simple and feasible self-adjusting contact performance is constructed, which provides a novel technical approach for lithium metal battery to obtain higher energy density and better cycle stability. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 Optical photos of gels and batteries

[0018] In the figure: (a) is the optical photo of the synthesized gel electrolyte after standing at room temperature for 6h; (b) is the optical photo of the soft pack battery obtained after secondary injection.

[0019] Figure 2 Infrared spectrum of the synthesized gel electrolyte

[0020] In the figure: - is the infrared spectrum of the gel sample (a), ··· is the infrared spectrum of ethylene glycol dimethyl ether (b), and -·- is the infrared spectrum of 1,3-dioxolane (c);

[0021] The X-axis is the wave number, and the unit is cm -1 ; the Y-axis is the transmittance of the signal, and the unit is %.

[0022] Figure 3 Cycle performance diagram of lithium metal battery (lithium-sulfur soft pack battery)

[0023] In the figure: the current density is 0.1C, wherein 1C=1000mAh / g;

[0024] The abscissa is the cycle number, and the unit is n; the ordinate is the discharge specific capacity, and the unit is mAh / g; the right ordinate is the coulombic efficiency, and the unit is %.

[0025] Figure 4 Rate performance diagram of lithium metal battery

[0026] In the figure: 1C=1000mAh·g -1 , in the figure, ● is the discharge specific capacity curve, and ○ is the coulombic efficiency curve;

[0027] The abscissa is the cycle number, and the unit is n; the ordinate is the discharge specific capacity, and the unit is mAh / g; the right ordinate is the coulombic efficiency, and the unit is %. DETAILED DESCRIPTION

[0028] The application will be described in further detail below in conjunction with the drawings and examples.

[0029] Example 1

[0030] Dissolve 1.5 M LiTFSI in a solvent prepared by mixing 1,3-dioxolane and diethyleneglycol dimethyl ether at a volume ratio of 9:1, and stir at room temperature at a rotation speed of 100 rpm under an argon atmosphere for 24 h to completely dissolve the lithium salt. Then, dissolve the initiator in the electrolyte, and stir at a rotation speed of 100 rpm under an argon atmosphere for 0.5 h, and then inject into the battery. After standing at room temperature for 12 h, add 1 ml of electrolyte without the initiator.

[0031] Figure 1 Optical photograph of the gel electrolyte synthesized in Example 1 after standing at room temperature for 12 h (a) and optical photograph of the electrolyte B after injection into the battery (b). As can be seen from the photographs, the gel electrolyte can be gelled after standing at room temperature for 12 h. Figure 1 Figure 2 Infrared graph of the gel electrolyte synthesized in Example 1. As can be seen from the test results, DOL is subjected to ring-opening reaction under the initiation of aluminum chloride, and then gelling reaction occurs.

[0032] Example 2

[0033] Dissolve 3 M LiFSI and LiBF4 mixed lithium salt in a solvent prepared by mixing 1,3-dioxolane (DOL) and dimethyl ether at a volume ratio of 5:5, and stir at room temperature at a rotation speed of 150 rpm under an argon atmosphere for 24 h to completely dissolve the lithium salt. Then, dissolve the initiator in the electrolyte, and stir at a rotation speed of 150 rpm under an argon atmosphere for 12 h, and then inject into the battery. After standing at room temperature for 18 h, add 2 ml of electrolyte without the initiator.

[0034] Figure 3 Cycle performance graph of the lithium metal battery (lithium-sulfur soft pack battery) prepared in Example 2 based on the method of the present application. In the voltage range of 1.8 to 2.5 V, at a current density of 0.1 C (1 C = 1000 mA / g), the initial discharge specific capacity is 1382.6 mAh / g, the first coulombic efficiency is 96.2%, and the reversible capacity is 693.2 mAh / g after 250 cycles. As can be seen from this, the lithium metal battery prepared by the method of the present application exhibits high specific capacity and excellent cycle stability.

[0035] Example 3

[0036] ​The mixed lithium salt with a total concentration of 5M LiTFSI and LiNO3 was dissolved in a solvent of 1,3-dioxolane DOL and tetraethylene glycol dimethyl ether mixed in a volume ratio of 3:7, stirred at room temperature at a speed of 200 rpm for 24 h under a protective atmosphere to completely dissolve the lithium salt; then the initiator was dissolved in the electrolyte, stirred at a speed of 200 rpm for 24 h under a protective atmosphere, injected into the battery, and then placed at room temperature for 24 h, and then 10 ml of electrolyte without initiator was added.

[0037] Figure 4 The rate performance graph of the lithium metal battery prepared according to the method of Example 3 based on the present application. The reversible discharge specific capacity of the electrode material was 1203 mAh / g, 858 mAh / g, and 832 mAh / g at a current density of 0.1C, 0.2C, and 0.5C, respectively. When the current density returned to 0.1C, the reversible capacity was 889 mAh / g. It can be seen that the lithium-sulfur battery soft pack battery prepared by the method of the present application exhibits excellent rate performance.

Claims

1. A method for preparing an in-situ gel, characterized in that: The preparation method involves the following steps: Lithium salt was dissolved in a solvent composed of 1,3-dioxolane DOL and straight-chain ether organic compounds. The mixture was stirred at 100–200 rpm for 24 hours at room temperature under an argon atmosphere to ensure complete dissolution of the lithium salt. Then, the initiator was dissolved in the electrolyte and stirred at 100–200 rpm for 0.5–24 hours under an argon atmosphere. The solution was then injected into the battery and allowed to stand at room temperature for 12–24 hours. Finally, 1–10 ml of electrolyte without the initiator was added. The lithium salt is one or more of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium hexafluorophosphate (LiPF6), lithium nitrate (LiNO3), and lithium tetrafluoroborate (LiBF4), and the total concentration of the lithium salt is 0.1–5 M. The straight-chain ether organic compound is one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether; the volume ratio of 1,3-dioxolane DOL to the straight-chain ether organic compound is 9:1 to 3:7; The initiator is a Lewis acid, and is one or more of aluminum chloride, ferric chloride, boron trifluoride, niobium pentachloride, and trifluoromethanesulfonate, and is used in an amount of 0.1 to 10 mM; The initiator-free electrolyte is one or more of ether-based electrolytes and carbonate-based electrolytes; The ether electrolyte is one or more of tetrahydrofuran (THF), 2-methyltetrahydrofuran (2me-thf), 1,3-dioxolane (DOL), dimethoxymethane (DMM), 1,2-dimethoxyethane (DME), and diethylene glycol dimethyl ether (DG). The carbonate electrolyte is one or more of propylene carbonate (PC), ethylene carbonate (EC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), methyl acrylate (MA), and ethyl acrylate (EA).

2. The method for preparing an in-situ gel according to claim 1, characterized in that: The lithium anode is metallic lithium or a lithium alloy.

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