CN108232291A - A kind of non-carbonic ester low temperature molten salt electrolysis plastidome suitable for lithium titanate battery - Google Patents

Abstract

The invention relates to the field of lithium ion battery electrolytes. The invention provides a non-carbonate low-temperature molten salt electrolyte system suitable for lithium titanate (Li ₄ Ti ₅ O ₁₂ ) batteries. The electrolyte system involved in the present invention is prepared by melting lithium salt and one or several solid reagents containing cyano or amino functional groups at low temperature, does not contain any non-carbonate solvents, and can improve the safety performance and electrochemical performance of lithium-ion batteries. performance.

Description

A non-carbonate low-temperature molten salt electrolyte system suitable for lithium titanate batteries

technical field

The invention relates to a low-temperature molten salt electrolyte, in particular to a non-carbonate low-temperature molten salt electrolyte system suitable for lithium titanate batteries.

Background technique

Molten salt refers to a melt composed of metal cations and non-metal anions, mainly including room temperature molten salt (ie, room temperature ionic liquid) and high temperature molten salt. Because of its non-volatile, non-flammable, high thermal and electrochemical stability, good safety and wide liquid range, it can be considered as an electrolyte for lithium-ion batteries. Lithium-ion battery electrolytes have a very important impact on the performance of lithium-ion batteries. Compared with traditional liquid electrolytes, molten salt electrolytes do not use organic carbonates as solvents, which can effectively reduce the safety hazards of lithium-ion batteries and improve the performance of lithium-ion batteries. Battery safety performance and range of use. At the same time, molten salt electrolytes have high ionic conductivity, wide electrochemical stability window, excellent oxidation resistance, and have good application prospects in lithium-ion batteries. However, the application and research of molten salt electrolytes in lithium-ion batteries are less, and most of them are used in storage batteries and solar cells. At present, molten salt electrolytes that are widely studied are prepared by organic ionic liquids and lithium salts. Due to the low ionic conductivity of lithium-ion batteries prepared by organic ionic liquids at room temperature, the highest can only reach 10 ^-4 S cm ^-2 , which is difficult to meet The requirements of commercial lithium-ion batteries are difficult to be applied on a large scale at room temperature. On the other hand, the high price of ionic liquid will greatly increase the production cost of lithium-ion batteries. Therefore, there is a need to develop molten salt electrolyte systems with high ionic conductivity at room temperature and low cost.

Traditional liquid lithium-ion battery electrolytes mostly use organic carbonates as solvents. However, in the process of charging from 1.55 V to 1.75 V, the lithium titanate negative electrode will catalyze side reactions with carbonate solvents to produce hydrogen and olefin gases, causing flatulence, greatly reducing the safety performance and cycle performance of the battery, and seriously hindering the development of lithium titanate. The commercialization process of lithium titanate battery. Therefore, it is of great significance to develop new non-carbonate esters that do not produce gas and are suitable for lithium titanate-based lithium-ion battery electrolytes.

Contents of the invention

The object of the present invention is to provide a non-carbonate low-temperature molten salt electrolyte system suitable for lithium titanate batteries.

In order to achieve the above object, the technical scheme adopted in the present invention is:

A non-carbonate low-temperature molten salt electrolyte system suitable for lithium titanate (Li ₄ Ti ₅ O ₁₂ ) batteries. The non-carbonate low-temperature molten salt electrolyte is melted at low temperature by a lithium salt and a solid reagent containing cyano or amino functional groups preparation.

The solid reagent containing cyano or amino functional groups is one or more of urea, succinonitrile, acetamide, urethane, melamine, iminodicarbonic acid diamide, dimethyl urea, and ethylene urea. ; The lithium salt is lithium bisoxalate borate (LiBOB), lithium difluorooxalate borate (LiDFOB), lithium hexafluorophosphate (LiPF ₆ ), lithium perchlorate (LiClO ₄ ), bistrifluoromethylsulfonylimide One or more of lithium (LiTFSI), lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ), lithium tetrafluoroborate (LiBF ₄ ), lithium nitrate (LiNO ₃ ); the melting temperature of the low-temperature molten salt electrolyte is -10 ~ 60°C; the melting temperature of the preferred low temperature molten salt electrolyte is 0 ~ 50 ^o C; the concentration of lithium salt in the low temperature molten salt electrolyte is 0.1 ~ 6 mol/L; The concentration is 0.5 ~ 3 mol/L.

A lithium titanate battery. The lithium titanate battery is composed of a positive electrode, a diaphragm, a negative electrode and an electrolyte. The electrolyte adopts the above-mentioned low-temperature molten salt electrolyte system.

The positive electrode active material of the lithium titanate (Li ₄ Ti ₅ O ₁₂ ) battery is one of lithium iron phosphate, lithium iron manganese phosphate, lithium cobaltate, lithium manganate, nickel-cobalt-manganese ternary material, and lithium nickel-manganese oxide , the negative electrode active material is lithium titanate; the separator used in the lithium titanate (Li ₄ Ti ₅ O ₁₂ ) battery is polypropylene film, cellulose non-woven fabric film, polyimide, polyethylene terephthalate Alcohol ester film (PET film), one of glass fiber separators.

A preparation method of the lithium titanate battery described above, the positive and negative electrodes are separated by a diaphragm, and the low-temperature molten salt electrolyte described in claim 1 is injected into the battery.

The advantages that the present invention has:

The invention provides a non-carbonate low-temperature molten salt electrolyte system suitable for lithium titanate batteries. The electrolyte is prepared by melting one or several cheap solid reagents containing cyano groups or amino groups and lithium salts at low temperature. The preparation process is simple and easy to operate. From the perspective of operation process and cost, it is easy to realize commercialization.

The ion conductivity of the low-temperature molten salt electrolyte system proposed by the present invention at room temperature is equivalent to that of the traditional carbonate solvent liquid electrolyte, both of which can reach 10 ^-3 S cm ^-2 . The electrochemical window at room temperature of traditional liquid electrolytes using carbonate solvents is below 4.5 V, while the electrochemical window at room temperature of the low-temperature molten salt electrolyte system provided by the present invention can reach 4.7 V.

The invention provides a molten salt electrolyte system which can improve the safety performance and ion conductivity of lithium titanate batteries. The impedance value of the pouch battery assembled with lithium titanate as the negative electrode using this electrolyte is 0.4 ~ 1.5 Ω, which is smaller than the impedance value (1.87 Ω) of the battery assembled with the liquid electrolyte using carbonate solvent under the same conditions.

The lithium titanate battery assembled with the low-temperature molten salt electrolyte system proposed by the present invention has a thickness of 2.83 mm before the charge and discharge test, and the thickness of the battery is 2.87 mm after 300 cycles. The thickness of the battery assembled with the liquid electrolyte of carbonate solvent was 2.81 mm before the test, and the thickness of the battery after 300 cycles was 7.23 mm. The low-temperature molten salt electrolyte effectively solved the gas problem of the lithium titanate battery and improved the safety performance of the battery. .

specific implementation plan

The invention provides a molten salt electrolyte prepared by melting a solid compound containing a cyano group or an amino group and a lithium salt at a low temperature, and is applied in a soft-pack battery with lithium titanate as a negative electrode.

comparative example

In a glove box filled with argon, use a pipette gun to measure 10 mL of EC:DMC (V:V=1:1), weigh 2.89 g of LiTFSI solid in a 20 mL sample bottle with an analytical balance, and place in a glove box at room temperature Dissolve under stirring to obtain a uniform and transparent electrolyte.

Example 1

In a glove box filled with argon, use an analytical balance to weigh 5 g of succinonitrile solid, 3 g of urea solid, 2 g of acetamide solid, 3 g of LiTFSI solid, and 1 g of LiNO ₃ solid in a 20 mL sample bottle, and place in- Under the condition of 10 ^o C, stir and dissolve with a magnetic stirrer to obtain a uniform and transparent solution.

Example 2

In a glove box filled with argon gas, 3 g of succinonitrile solid, 5 g of urea solid, 2 g of acetamide solid, and 0.1 g of LiTFSI solid were weighed with an analytical balance in a ²⁰ mL sample bottle. Agitate and dissolve with a stirrer to obtain a homogeneous and transparent solution.

Example 3

In a glove box filled with argon gas, 2 g of succinonitrile solid, 3 g of urea solid, 5 g of acetamide solid, and ₃ g of LiNO solid were weighed with an analytical balance in a ²⁰ mL sample bottle. Stir and dissolve with a magnetic stirrer to obtain a uniform and transparent solution.

Example 4

In a glove box filled with argon, use an analytical balance to weigh 2 g of succinonitrile solid, 5 g of iminodicarbonic acid diamide solid, 3 g of acetamide solid, and 3 g of LiTFSI solid in a 20 mL sample bottle, at 20 ^o Under the condition of C, stir and dissolve with a magnetic stirrer to obtain a uniform and transparent solution.

Example 5

In a glove box filled with argon, use an analytical balance to weigh 6 g of succinonitrile solid, 4 g of urea solid, and 3 g of LiBF ₄ solid in a 20 mL sample bottle, stir and dissolve with a magnetic stirrer at 30 ^o C A homogeneous and transparent solution was obtained.

Example 6

In a glove box filled with argon, use an analytical balance to weigh 6 g of succinonitrile solid, 4 g of acetamide solid, and 3 g of LiTFSI solid in a 20 mL sample bottle, and stir and dissolve with a magnetic stirrer at 40 ^o C. A homogeneous and transparent solution was obtained.

Example 7

In a glove box filled with argon, use an analytical balance to weigh 6 g of urea solid, 4 g of ethyl carbamate solid, and 3 g of LiTFSI solid in a 20 mL sample bottle, and stir and dissolve with a magnetic stirrer at 45 ^o C. A homogeneous and transparent solution was obtained.

Example 8

In a glove box filled with argon, use an analytical balance to weigh 12 g of urea solid, 12 g of acetamide solid, 5 g of LiTFSI solid, and 5 g of LiClO ₄ solid in a 20 ^mL sample bottle. Dissolve with stirring to obtain a homogeneous and transparent solution.

Example 9

In a glove box filled with argon, use an analytical balance to weigh 7 g of acetamide solid, 6 g of succinonitrile, and 3 g of gLiTFSI solid in a 20 mL sample bottle, stir and dissolve with a magnetic stirrer at 55 ^o C to obtain a uniform Clear solution.

Example 10

In a glove box filled with argon, use an analytical balance to weigh 6 g of succinonitrile, 7 g of acetamide solid, and 5 g of LiClO ₄ solid in a 20 mL sample bottle, stir and dissolve with a magnetic stirrer at 60 ^o C A homogeneous and transparent solution was obtained.

Cell preparation:

(1) Lithium titanate (LTO) pole piece preparation: Dissolve polyvinylidene fluoride (PVDF) in N-methylpyrrolidone (NMP) to prepare a 6% uniform transparent solution, weigh lithium titanate, acetylene black, PVDF , the mass ratio of carbon nanotubes is 92:2:4:2, stir to obtain a uniform negative electrode slurry, coat it on aluminum foil according to the surface density of 120 g/ ^m2 on one side, and place it in a 60 ^o C blast dryer 2 h, then transferred to 120 ^o C vacuum oven to dry for 10 h, and then rolled and cut to obtain the negative electrode sheet.

(2) Ionic conductivity battery assembly: Assemble the LIR2032 button cell from top to bottom in order of negative electrode, steel sheet, diaphragm, steel sheet, spring sheet, and positive electrode shell, and inject the molten salt prepared in Comparative Examples and Examples 1-10 The electrolyte was sealed with a sealing machine, and the obtained battery was left to stand at 60 ^o C for 12 hours. After returning to room temperature, the battery was tested for its ion conductivity at room temperature.

(3) Electrochemically stable window battery assembly: Assemble LIR2032 type button cells from top to bottom in order of negative electrode, lithium sheet, diaphragm, steel sheet, spring sheet, positive electrode case, and inject the molten metal prepared in Comparative Examples and Examples 1-10. The salt electrolyte was sealed with a sealing machine, and the obtained battery was left to stand at 60 ^o C for 12 hours. After returning to room temperature, the battery was tested for the electrochemical stability window at room temperature.

(4) Lithium titanate battery preparation: weld the positive and negative electrodes to the tabs and separate them with a diaphragm, assemble them by stacking them, package them with aluminum-plastic film, and inject the molten metal prepared in Comparative Examples and Examples 1-10 into the glove box. Salt electrolyte, battery preparation is complete. The obtained batteries were left to stand at 60 ^o C for 12 h, and the batteries were tested after returning to room temperature. All battery negative electrodes in the comparative examples and examples are lithium titanate, and the positive electrode material is one of lithium iron phosphate, lithium iron manganese phosphate, lithium cobalt oxide, lithium manganate, nickel-cobalt-manganese ternary material, and lithium nickel manganese oxide. The proportion and method of preparing the positive pole piece are the same as those of the lithium titanate negative pole.

(5) Lithium titanate battery flatulence test: test the thickness of the battery assembled in (2) at room temperature, and then perform a constant current redischarge cycle for 300 cycles under the condition of 85 mAg ^-1 , and then test the battery thickness again.

The ionic conductivity of the battery, the internal resistance of the electrochemical stability window and the thickness expansion rate of the battery after 300 cycles were tested by comparing the comparative examples and Examples 1-10. The results obtained are shown in Table 1:

Table 1 Ionic conductivity, electrochemical stability window, internal resistance, and thickness expansion rate of the batteries of Comparative Examples and Examples 1-10 after 300 cycles

Claims (6)

1. one kind is suitable for lithium titanate (Li₄Ti₅O₁₂) battery non-carbonic ester low temperature molten salt electrolysis plastidome, it is characterised in that：It is non- Carbonic ester low temperature molten salt electrolysis matter is melted preparation by the solid reagent of lithium salts and cyano-containing or amido functional group at low temperature.

It is 2. according to claim 1 a kind of suitable for lithium titanate (Li₄Ti₅O₁₂) battery non-carbonic ester low temperature molten salt electrolysis Plastidome, it is characterised in that：The solid reagent containing cyano or amido functional group for urea, succinonitrile, acetamide, One or more of urethane vinegar, melamine, imino-diacetic carbamide, dimethyl urea, ethylene urea；Described Lithium salts is biethyl diacid lithium borate（LiBOB）, difluorine oxalic acid boracic acid lithium（LiDFOB）, lithium hexafluoro phosphate（LiPF₆）, lithium perchlorate （LiClO₄）, bis trifluoromethyl sulfimide lithium（LiTFSI）, trifluoromethyl sulfonic acid lithium（LiCF₃SO₃）, LiBF4 （LiBF₄）, lithium nitrate（LiNO₃）One or more of；The melting temperature of low temperature molten salt electrolysis matter is -10 ~ 60 DEG C；Low temperature A concentration of 0.1 ~ 6 mol/L of lithium salts in molten salt electrolyte.

3. a kind of lithium titanate battery, lithium titanate battery is made of anode, diaphragm, cathode and electrolyte, it is characterised in that：Electrolysis Matter uses low temperature molten salt electrolysis plastidome described in claim 1.

4. a kind of lithium titanate battery according to claim 3, it is characterised in that：Lithium titanate (the Li₄Ti₅O₁₂) battery is just Pole active material is one in LiFePO4, lithium ferric manganese phosphate, cobalt acid lithium, LiMn2O4, nickel-cobalt-manganese ternary material, nickel ion doped Kind, negative electrode active material is lithium titanate；Lithium titanate (the Li₄Ti₅O₁₂) diaphragm that uses of battery is polypropylene film, cellulose Non-woven membrane, polyimides, pet film（PET film）, one kind in fibreglass diaphragm.

5. a kind of preparation method of the lithium titanate battery described in claim 3, it is characterised in that：Positive and negative anodes by membranes apart, It and will be in the low temperature molten salt electrolysis matter injection battery described in claim 1.

6. a kind of preparation method of lithium titanate battery according to claim 5, it is characterised in that：The lithium titanate (Li₄Ti₅O₁₂) battery anode active material for LiFePO4, lithium ferric manganese phosphate, cobalt acid lithium, LiMn2O4, nickel-cobalt-manganese ternary material, One kind in nickel ion doped, negative electrode active material are lithium titanate；Lithium titanate (the Li₄Ti₅O₁₂) diaphragm that uses of battery is poly- Polypropylene film, cellulosic nonwoven fabric film, polyimides, pet film（PET film）, glass fibre every One kind in film.