CN114388889B - Lithium ion battery electrolyte suitable for high-capacity micron alloy negative electrode, battery and electronic device - Google Patents

Lithium ion battery electrolyte suitable for high-capacity micron alloy negative electrode, battery and electronic device Download PDF

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CN114388889B
CN114388889B CN202111645751.5A CN202111645751A CN114388889B CN 114388889 B CN114388889 B CN 114388889B CN 202111645751 A CN202111645751 A CN 202111645751A CN 114388889 B CN114388889 B CN 114388889B
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CN114388889A (en
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王飞
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Fudan University
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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
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
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    • H01M10/0567—Liquid materials characterised by the additives
    • 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
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
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    • H01M10/0568—Liquid materials characterised by the solutes
    • 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
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0569—Liquid materials characterised by the solvents
    • 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
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/4235—Safety or regulating additives or arrangements in electrodes, separators or electrolyte

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Abstract

The invention relates to a lithium ion battery electrolyte suitable for a high-capacity micron alloy negative electrode, a battery and an electronic device. Also comprises a reducing additive; in the electrolyte, the mass fraction of the ether bond-containing compound is 65-98%, the mass fraction of the reducing additive is 0.01-5%, and the concentration of the lithium salt is 0.1-3mol/L. The ether bond-containing compound comprises at least one of tetrahydrofuran, 2-methyltetrahydrofuran, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether or tetraethylene glycol dimethyl ether. The reducing additive includes lithium difluorophosphate, lithium difluorooxalato borate, lithium bisoxalato borate, lithium difluorobisoxalato phosphate, lithium difluorooxalato borate, lithium tetrafluoroborate, lithium borohydride or lithium hydride. Compared with the prior art, the invention has the advantages of improving the circulation stability of the high-capacity micron alloy anode material, improving the high-voltage performance of the ether electrolyte, improving the electrochemical performance of the lithium ion battery based on the high-capacity micron alloy anode, and the like.

Description

Lithium ion battery electrolyte suitable for high-capacity micron alloy negative electrode, battery and electronic device
Technical Field
The invention relates to the field of electrochemistry, in particular to battery electrolyte suitable for a high-capacity micron alloy negative electrode, a lithium ion battery and an electronic device.
Background
Currently commercialized Lithium Ion Batteries (LIBs) mainly use graphite as a negative electrode. The lithium ion battery has good conductivity and a good layered structure, is favorable for lithium ion intercalation/deintercalation, but has low theoretical specific capacity (about 372 mAh/g), and the current practical application is close to the theoretical limit, so that the high requirement of the rapidly-developed electric automobile and energy storage power station on LIBs (light-induced emission) energy density cannot be met. Compared with graphite, the alloy anode material has higher theoretical capacity (for example, 4200mA/g when the silicon anode is fully lithiated), and has wide sources, thus being considered as an ideal choice of the anode of the high specific energy lithium ion battery. However, the large volume change of the alloy type negative electrode in the charge and discharge process can cause the change and even collapse of the electrode material structure, so that the cycling stability is poor, and the practical application of the alloy type negative electrode is restricted.
In recent years, numerous researchers have made extensive researches for solving the problem of poor cycle performance of alloy anode materials due to volume expansion, and the main solution is to alleviate the volume expansion by nanocrystallization of materials and surface solid electrolyte membranes (SEIs) so as to improve the cycle performance to a certain extent. However, repeated volume expansion/contraction of the material inevitably causes continuous rupture and reconstruction of the SEI, resulting in continuous decomposition of the electrolyte at the surface of the negative electrode, continuous increase in SEI thickness, decrease in battery Coulomb Efficiency (CE), increase in internal resistance, and continuous decay of capacity. The electrochemical performance of the alloy cathode can be further improved by adding a film forming additive (such as FEC, VC and the like) into the electrolyte to assist in forming a relatively stable SEI film, but the problem can not be fundamentally solved.
Disclosure of Invention
The invention aims to overcome the defects in the prior art and provide the lithium ion battery electrolyte, the battery and the electronic device which are suitable for the high-capacity micro-alloy negative electrode, and are used for improving the circulation stability of the high-capacity micro-alloy negative electrode material, improving the high-voltage performance of the ether electrolyte and improving the electrochemical performance.
The aim of the invention can be achieved by the following technical scheme:
the inventors have appreciated that to date, no modified LIBs electrolyte has been available that can provide a microalloyed negative electrode with an average CE of greater than 99.9%. The invention provides a lithium ion electrolyte with relatively stable thermodynamics based on an ether-based solvent with relatively high reduction stability; the synergy between different ethers in the mixed solvent can better stabilize the interface property of the alloy negative electrode I electrolyte compared with the single ether, so that the lithium ion battery adopting the electrolyte system has excellent long-cycle stability, and the specific scheme is as follows:
a lithium ion battery electrolyte suitable for a high-capacity micron alloy cathode comprises a compound containing ether bonds and lithium salt.
The invention provides a lithium ion electrolyte with relatively stable thermodynamics based on an ether-based solvent with relatively high reduction stability; the synergy between different ethers in the mixed solvent can better stabilize the interface property of the alloy negative electrode I electrolyte compared with the single ether, so that the lithium ion battery adopting the electrolyte system has excellent long-cycle stability; the electrolyte is simple in composition, low in cost and high in practicability.
Further, the electrolyte also includes a reducing additive;
in the electrolyte, the mass fraction of the ether bond-containing compound is 65-98%, the mass fraction of the reducing additive is 0.01-5%, and the concentration of the lithium salt is 0.1-3mol/L.
Further, the ether bond-containing compound comprises at least one of tetrahydrofuran, 2-methyltetrahydrofuran, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether or tetraethylene glycol dimethyl ether. Tetrahydrofuran and tetraethyleneglycol dimethyl ether are preferred, tetrahydrofuran, 2-methyltetrahydrofuran and tetraethyleneglycol dimethyl ether may also be preferred, and tetrahydrofuran, 2-methyltetrahydrofuran, triethyleneglycol dimethyl ether and tetraethyleneglycol dimethyl ether may also be preferred.
Further, the reducing additive comprises lithium difluorophosphate (LiPO 2 F 2 ) Lithium difluorooxalato borate (LiODFB), lithium bisoxalato borate (LiBOB), lithium difluorobisoxalato phosphate (LiDFOP), lithium difluorooxalato borate (LiDFOB), and lithium tetrafluoroborate (LiBF) 4 ) Lithium borohydride (LiBH) 4 ) Or lithium hydride (LiH).
Further, the lithium salt includes LiPF 6 。
A lithium ion battery comprising an electrolyte as described above, a microalloy negative electrode, a positive electrode, and a separator.
Further, the micro-alloy anode comprises 50-95wt% of anode active material. The balance of conductive carbon and binder with a mass ratio of about 2:1.
Further, the negative electrode active material includes Si, sn, bi, ge, al having a particle diameter of 1 to 50 μm.
Further, the positive electrode comprises a positive electrode active material, specifically S, se and Li 2 S, LFP, LCO, LMO, NCM or NCA.
An electronic device comprising a lithium ion battery as described above.
Compared with the prior art, the invention has the following advantages:
(1) The invention provides a lithium ion battery electrolyte with higher reduction stability, wherein the LiPF 6 As a lithium salt, liF can be reduced to anode surface without producing organic by-products; ether-based solvents such as tetrahydrofuran, 2-methyltetrahydrofuran, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether and the like have lower LUMO energy level and thermodynamic reduction potential (0.0-0.3V vs Li/Li) + ) And limited solvation ability for Li salts, so that SEI films are preferentially formed from LiPF during the entire lithiation process 6 Reduced formation, with fewer organic components, is in sharp contrast to the mixed organic-inorganic composition of conventional SEIs. The high-modulus LiF-organic double-layer interface formed in the electrolyte can adapt to the volume change of the alloy cathode in the circulating process, so that the circulating stability of the micron alloy cathode is improved;
(2) The additive introduced into the non-aqueous electrolyte of the lithium ion battery can be decomposed on the surface of the positive electrode to form a passivation film in preference to a solvent, so that the decomposition of other components in the electrolyte on the positive electrode side is avoided, the corrosion of HF in the electrolyte to the positive electrode material and the dissolution of transition metal are prevented, and the cycle performance of the positive electrode material in the ether-based electrolyte is improved;
(3) The mixed ether and the additive can modify the interface of the negative electrode, stabilize the micron alloy negative electrode, simultaneously can effectively form a film on the positive electrode, stabilize the structure of the positive electrode material and effectively improve the voltage application range of the ether electrolyte;
(4) According to the invention, through optimizing the formula of the electrolyte, particularly the mixed ether such as tetrahydrofuran, 2-methyltetrahydrofuran, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether and the like and combining the use of the reducing additive, the synergistic effect is finally exerted, the problem of the cycle stability of the micron alloy cathode can be effectively improved, and the electrochemical performance of the micron alloy-based lithium ion battery is obviously improved.
Drawings
FIG. 1 is an SEM image of micrometer Si used in examples 1-24;
FIG. 2 is an XRD pattern for micron Si used in examples 1-24;
FIG. 3 is a graph showing the cycle performance and coulombic efficiency of the micro Si negative electrodes obtained in example 1 and comparative examples 1-4;
FIG. 4 shows the charge-discharge curve and cycle performance of example 12;
FIG. 5 is the cycle performance curves versus coulombic efficiency for example 1, example 5 and example 10;
FIG. 6 boron content of the electrolyte after various cycles of example 16.
Detailed Description
The invention will now be described in detail with reference to the drawings and specific examples. The present embodiment is implemented on the premise of the technical scheme of the present invention, and a detailed implementation manner and a specific operation process are provided, but the protection scope of the present invention is not limited to the following embodiments.
A lithium ion battery includes an electrolyte, a microalloy negative electrode, a positive electrode, and a separator.
The micro-alloy anode comprises 50-95wt% of anode active material. The negative electrode active material includes Si, sn, bi, ge, al having a particle diameter of 1 to 50 μm.
The positive electrode comprises positive electrode active material, specifically S, se and Li 2 S, LFP, LCO, LMO, NCM or NCA.
The electrolyte includes an ether bond-containing compound and a lithium salt. Also comprises a reducing additive; in the electrolyte, the mass fraction of the ether bond-containing compound is 65-98%, the mass fraction of the reducing additive is 0.01-5%, and the concentration of the lithium salt is 0.1-3mol/L.
The ether bond-containing compound comprises at least one of tetrahydrofuran, 2-methyltetrahydrofuran, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether or tetraethylene glycol dimethyl ether. Tetrahydrofuran and tetraethyleneglycol dimethyl ether are preferred, tetrahydrofuran, 2-methyltetrahydrofuran and tetraethyleneglycol dimethyl ether may also be preferred, and tetrahydrofuran, 2-methyltetrahydrofuran, triethyleneglycol dimethyl ether and tetraethyleneglycol dimethyl ether may also be preferred.
The reducing additive comprises lithium difluorophosphate, lithium difluorooxalato borate, lithium bisoxalato borate, lithium difluorobisoxalato phosphate, lithium difluorooxalato borate and tetrafluoroboric acidOne or more of lithium, lithium borohydride, or lithium hydride. The lithium salt comprises LiPF 6 。
Example 1
An electrolyte is prepared: tetrahydrofuran and tetraethyleneglycol dimethyl ether are mixed according to the volume ratio of 1:1, and 1mol/L lithium hexafluorophosphate (LiPF) is added after the mixing 6 ) And (3) completely dissolving to obtain the lithium ion battery electrolyte. The cycling stability of the micron silicon cathode in the electrolyte is tested by adopting 325-mesh micron silicon powder as an electrode active substance (Si content accounts for 70wt% of the total mass of the electrode) and assembling a Si I Li semi-battery.
Example 2
An electrolyte is prepared: tetrahydrofuran and tetraethyleneglycol dimethyl ether are mixed according to the volume ratio of 1:1, and 2mol/L lithium hexafluorophosphate (LiPF) is added after the mixing 6 ) And (3) completely dissolving to obtain the lithium ion battery electrolyte. The cycling stability of the micron silicon cathode in the electrolyte is tested by adopting 325-mesh micron silicon powder as an electrode active substance (Si content accounts for 70wt% of the total mass of the electrode) and assembling a Si I Li semi-battery.
Example 3
An electrolyte is prepared: tetrahydrofuran and tetraethyleneglycol dimethyl ether are mixed according to the volume ratio of 3:1, and 1mol/L lithium hexafluorophosphate (LiPF) is added after the mixing 6 ) And (3) completely dissolving to obtain the lithium ion battery electrolyte. The cycling stability of the micron silicon cathode in the electrolyte is tested by adopting 325-mesh micron silicon powder as an electrode active substance (Si content accounts for 70wt% of the total mass of the electrode) and assembling a Si I Li semi-battery.
Example 4
An electrolyte is prepared: tetrahydrofuran and tetraethyleneglycol dimethyl ether are mixed according to the volume ratio of 1:3, and 1mol/L lithium hexafluorophosphate (LiPF) is added after the mixing 6 ) And (3) completely dissolving to obtain the lithium ion battery electrolyte. The cycling stability of the micron silicon cathode in the electrolyte is tested by adopting 325-mesh micron silicon powder as an electrode active substance (Si content accounts for 70wt% of the total mass of the electrode) and assembling a Si I Li semi-battery.
Example 5
An electrolyte is prepared: tetrahydrofuran, 2-methyltetrahydrofuran and tetraethylGlycol dimethyl ether is mixed according to the volume ratio of 1:1:1, and 1.0mol/L lithium hexafluorophosphate (LiPF) is added after mixing 6 ) And (3) completely dissolving to obtain the lithium ion battery electrolyte. The cycling stability of the micron silicon cathode in the electrolyte is tested by adopting 325-mesh micron silicon powder as an electrode active substance (Si content accounts for 70wt% of the total mass of the electrode) and assembling a Si I Li semi-battery.
Example 6
An electrolyte is prepared: tetrahydrofuran, 2-methyltetrahydrofuran and tetraethyleneglycol dimethyl ether are mixed according to the volume ratio of 45:45:10, and 1mol/L lithium hexafluorophosphate (LiPF) is added after mixing 6 ) And (3) completely dissolving to obtain the lithium ion battery electrolyte. The cycling stability of the micron silicon cathode in the electrolyte is tested by adopting 325-mesh micron silicon powder as an electrode active substance (Si content accounts for 70wt% of the total mass of the electrode) and assembling a Si I Li semi-battery.
Example 7
An electrolyte is prepared: tetrahydrofuran, 2-methyltetrahydrofuran, triethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether are mixed according to the volume ratio of 1:1:1:1, and 1mol/L lithium hexafluorophosphate (LiPF) is added after mixing 6 ) And (3) completely dissolving to obtain the lithium ion battery electrolyte. The cycling stability of the micron silicon cathode in the electrolyte is tested by adopting 325-mesh micron silicon powder as an electrode active substance (Si content accounts for 70wt% of the total mass of the electrode) and assembling a Si I Li semi-battery.
Example 8
An electrolyte is prepared: mixing 2-methyltetrahydrofuran, triethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether according to the volume ratio of 45:45:10, adding 1mol/L lithium hexafluorophosphate (LiPF) 6 ) And (3) completely dissolving to obtain the lithium ion battery electrolyte. The cycling stability of the micron silicon cathode in the electrolyte is tested by adopting 325-mesh micron silicon powder as an electrode active substance (Si content accounts for 70wt% of the total mass of the electrode) and assembling a Si I Li semi-battery.
Example 9
An electrolyte is prepared: tetrahydrofuran, 2-methyltetrahydrofuran and tetraethyleneglycol dimethyl ether are mixed according to the volume ratio of 1:1:1, and 1mol/L lithium hexafluorophosphate (LiPF) is added after mixing 6 ) After complete dissolution, 0.05wt% of lithium bisoxalato borate additive is added, and the lithium ion battery electrolyte is obtained after uniform stirring. The cycling stability of the micron silicon cathode in the electrolyte is tested by adopting 325-mesh micron silicon powder as an electrode active substance (Si content accounts for 70wt% of the total mass of the electrode) and assembling a Si I Li semi-battery.
Example 10
An electrolyte is prepared: tetrahydrofuran, 2-methyltetrahydrofuran and tetraethyleneglycol dimethyl ether are mixed according to the volume ratio of 1:1:1, and 1mol/L lithium hexafluorophosphate (LiPF) is added after mixing 6 ) After complete dissolution, 0.1wt% of lithium borohydride additive is added, and the lithium ion battery electrolyte is obtained after uniform stirring. The cycling stability of the micron silicon cathode in the electrolyte is tested by adopting 325-mesh micron silicon powder as an electrode active substance (Si content accounts for 70wt% of the total mass of the electrode) and assembling a Si I Li semi-battery.
Example 11
An electrolyte is prepared: tetrahydrofuran, 2-methyltetrahydrofuran and tetraethyleneglycol dimethyl ether are mixed according to the volume ratio of 45:45:10, and 2mol/L lithium hexafluorophosphate (LiPF) is added after mixing 6 ) And (3) completely dissolving to obtain the lithium ion battery electrolyte. LFP is used as electrode active material (the surface capacity is 2.5 mAh/cm) 2 ) The LFP Li half cell was assembled and the high voltage cycle performance of the electrolyte was tested.
Example 12
An electrolyte is prepared: tetrahydrofuran, 2-methyltetrahydrofuran and tetraethyleneglycol dimethyl ether are mixed according to the volume ratio of 45:45:10, and 2mol/L lithium hexafluorophosphate (LiPF) is added after mixing 6 ) And (3) completely dissolving to obtain the lithium ion battery electrolyte. LCO is used as electrode active material (the surface capacity is 2.5mAh/cm 2 ) LCO I Li half-cell is assembled, and the high-voltage cycle performance of the electrolyte is tested.
Example 13
An electrolyte is prepared: tetrahydrofuran, 2-methyltetrahydrofuran and tetraethyleneglycol dimethyl ether are mixed according to the volume ratio of 45:45:10, and 2mol/L lithium hexafluorophosphate (LiPF) is added after mixing 6 ) And (3) completely dissolving to obtain the lithium ion battery electrolyte. CollectingNCM811 was used as an electrode active material (the surface capacity was 3.0mAh/cm 2 ) The ncm||li half cell was assembled and the high voltage cycle performance of the electrolyte was tested.
Example 14:
an electrolyte is prepared: tetrahydrofuran, 2-methyltetrahydrofuran and tetraethyleneglycol dimethyl ether are mixed according to the volume ratio of 45:45:10, and 2mol/L lithium hexafluorophosphate (LiPF) is added after mixing 6 ) And (3) completely dissolving to obtain the lithium ion battery electrolyte. The positive electrode active material adopts LFP material (the surface capacity is 2.5 mAh/cm) 2 ) The negative electrode active material was 325 mesh micron silicon powder (Si content 70wt% of the total mass of the electrode). And assembling the positive electrode, the negative electrode and the electrolyte into a full battery for testing.
Example 15
An electrolyte is prepared: tetrahydrofuran, 2-methyltetrahydrofuran and tetraethyleneglycol dimethyl ether are mixed according to the volume ratio of 1:1:1, and 1mol/L lithium hexafluorophosphate (LiPF) is added after mixing 6 ) After complete dissolution, 0.01wt% of lithium bisoxalato borate additive is added, and the lithium ion battery electrolyte is obtained after uniform stirring. The positive electrode active material was made of NCM523 material (surface capacity 3.0mAh/cm 2 ) The negative electrode active material was 325 mesh micron silicon powder (Si content 70wt% of the total mass of the electrode). And assembling the anode, the cathode and the electrolyte into a battery for testing.
Example 16
An electrolyte is prepared: tetrahydrofuran, 2-methyltetrahydrofuran and tetraethyleneglycol dimethyl ether are mixed according to the volume ratio of 1:1:1, and 1mol/L lithium hexafluorophosphate (LiPF) is added after mixing 6 ) After complete dissolution, 0.05wt% of lithium borohydride additive is added, and the lithium ion battery electrolyte is obtained after uniform stirring. The positive electrode active material was made of NCM523 material (surface capacity 3.0mAh/cm 2 ) The negative electrode active material was 325 mesh micron silicon powder (Si content 70wt% of the total mass of the electrode). And assembling the anode, the cathode and the electrolyte into a battery for testing.
Example 17
An electrolyte is prepared: mixing tetrahydrofuran, 2-methyltetrahydrofuran and tetraethyleneglycol dimethyl ether according to a volume ratio of 1:1:1, and adding the mixture after mixing1mol/L lithium hexafluorophosphate (LiPF) 6 ) After complete dissolution, 0.1wt% of lithium borohydride additive is added, and the lithium ion battery electrolyte is obtained after uniform stirring. The positive electrode active material adopts LFP material (the surface capacity is 2.5 mAh/cm) 2 ) The negative electrode active material was 325 mesh micron silicon powder (Si content 70wt% of the total mass of the electrode). And assembling the anode, the cathode and the electrolyte into a battery for testing.
Example 18
An electrolyte is prepared: tetrahydrofuran, 2-methyltetrahydrofuran and tetraethyleneglycol dimethyl ether are mixed according to the volume ratio of 1:1:1, and 1mol/L lithium hexafluorophosphate (LiPF) is added after mixing 6 ) After complete dissolution, 0.05wt% of lithium hydride additive is added, and the lithium ion battery electrolyte is obtained after uniform stirring. The positive electrode active material adopts LFP material (the surface capacity is 2.5 mAh/cm) 2 ) The negative electrode active material was 325 mesh micron silicon powder (Si content 70wt% of the total mass of the electrode). And assembling the anode, the cathode and the electrolyte into a battery for testing.
Example 19
An electrolyte is prepared: tetrahydrofuran, 2-methyltetrahydrofuran and tetraethyleneglycol dimethyl ether are mixed according to the volume ratio of 1:1:1, and 1mol/L lithium hexafluorophosphate (LiPF) is added after mixing 6 ) And adding 5wt% of lithium bisoxalato borate additive after complete dissolution, and stirring uniformly to obtain the lithium ion battery electrolyte. The positive electrode active material was made of NCM523 material (surface capacity 3.0mAh/cm 2 ) The negative electrode active material was 325 mesh micron silicon powder (Si content 70wt% of the total mass of the electrode). And assembling the anode, the cathode and the electrolyte into a battery for testing.
Example 20
An electrolyte is prepared: tetrahydrofuran, 2-methyltetrahydrofuran and tetraethyleneglycol dimethyl ether are mixed according to the volume ratio of 1:1:1, and 1mol/L lithium hexafluorophosphate (LiPF) is added after mixing 6 ) After complete dissolution, adding 0.1wt% of lithium borohydride additive and 0.03wt% of lithium hydride, and stirring uniformly to obtain the lithium ion battery electrolyte. The positive electrode active material adopts LFP material (the surface capacity is 2.5 mAh/cm) 2 ) The negative electrode active material was 325 mesh micron silicon powder (Si content 70wt% of the total electrode mass)). And assembling the anode, the cathode and the electrolyte into a battery for testing.
Example 21
An electrolyte is prepared: tetrahydrofuran, 2-methyltetrahydrofuran and tetraethyleneglycol dimethyl ether are mixed according to the volume ratio of 1:1:1, and 1mol/L lithium hexafluorophosphate (LiPF) is added after mixing 6 ) After complete dissolution, 0.1wt% of lithium difluorooxalate borate additive and 0.15wt% of lithium tetrafluoroborate are added, and the lithium ion battery electrolyte is obtained after uniform stirring. The positive electrode active material adopts LFP material (the surface capacity is 2.5 mAh/cm) 2 ) The negative electrode active material was 325 mesh micron silicon powder (Si content 70wt% of the total mass of the electrode). And assembling the anode, the cathode and the electrolyte into a battery for testing.
Example 22
An electrolyte is prepared: tetrahydrofuran, 2-methyltetrahydrofuran and tetraethyleneglycol dimethyl ether are mixed according to the volume ratio of 1:1:1, and 1mol/L lithium hexafluorophosphate (LiPF) is added after mixing 6 ) After complete dissolution, 0.1wt% lithium borohydride additive, 0.1wt% lithium difluorophosphate (LiPO) was added 2 F 2 ) And (3) stirring 0.05 weight percent of lithium tetrafluoroborate uniformly to obtain the lithium ion battery electrolyte. The positive electrode active material was NCM811 material (surface area 3.0mAh/cm 2 ) The negative electrode active material was 325 mesh micron silicon powder (Si content 50wt% of the total mass of the electrode). And assembling the anode, the cathode and the electrolyte into a battery for testing.
Example 23
An electrolyte is prepared: tetrahydrofuran, 2-methyltetrahydrofuran and tetraethyleneglycol dimethyl ether are mixed according to the volume ratio of 1:1:1, and 1mol/L lithium hexafluorophosphate (LiPF) is added after mixing 6 ) After complete dissolution, 0.1wt% lithium borohydride additive, 0.1wt% lithium difluorophosphate (LiPO) was added 2 F 2 ) And (3) stirring 0.05 weight percent of lithium tetrafluoroborate uniformly to obtain the lithium ion battery electrolyte. The positive electrode active material was NCM811 material (surface area 3.0mAh/cm 2 ) The negative electrode active material was 325 mesh micron silicon powder (Si content 80wt% of the total mass of the electrode). And assembling the anode, the cathode and the electrolyte into a battery for testing.
Example 24
An electrolyte is prepared: tetrahydrofuran, 2-methyltetrahydrofuran and tetraethyleneglycol dimethyl ether are mixed according to the volume ratio of 1:1:1, and 1mol/L lithium hexafluorophosphate (LiPF) is added after mixing 6 ) After complete dissolution, 0.1wt% lithium borohydride additive, 0.1wt% lithium difluorophosphate (LiPO) was added 2 F 2 ) And (3) stirring 0.05 weight percent of lithium tetrafluoroborate uniformly to obtain the lithium ion battery electrolyte. The positive electrode active material was NCM811 material (surface area 3.0mAh/cm 2 ) The negative electrode active material was 325 mesh micron silicon powder (Si content 90wt% of the total mass of the electrode). And assembling the anode, the cathode and the electrolyte into a battery for testing.
In the invention, when preparing the electrolyte, 1mol/L lithium hexafluorophosphate solution is prepared first, and then the additive with corresponding mass is added according to the mass of the solution to obtain the electrolyte. In the invention, when the cathode is prepared, 325-mesh micron silicon powder is used as an electrode active substance, and the electrode also comprises conductive carbon and a binder in a mass ratio of about 2:1.
Comparative example 1
An electrolyte was provided for comparison: mixing Ethylene Carbonate (EC) and dimethyl carbonate (DMC) according to a volume ratio of 1:1, adding 1mol/L lithium hexafluorophosphate (LiPF) 6 ) And (3) completely dissolving to obtain the lithium ion battery electrolyte. The Si-Li half battery is assembled by adopting 325-mesh micron silicon powder as an electrode active substance (Si content accounts for 70wt% of the total mass of the electrode) and is used for comparing the performances of a micron silicon cathode in the electrolyte.
Comparative example 2
An electrolyte was provided for comparison: mixing Ethylene Carbonate (EC) and dimethyl carbonate (DMC) according to a volume ratio of 1:1, adding fluoroethylene carbonate with a volume fraction of 5% as an additive, uniformly mixing, and adding 1mol/L lithium hexafluorophosphate (LiPF) 6 ) And (3) completely dissolving to obtain the lithium ion battery electrolyte. The Si-Li half battery is assembled by adopting 325-mesh micron silicon powder as an electrode active substance (Si content accounts for 70wt% of the total mass of the electrode) and is used for comparing the performances of a micron silicon cathode in the electrolyte.
Comparative example 3
An electrolyte is prepared: and adding 1mol/L lithium hexafluorophosphate into the tetrahydrofuran solvent, and completely dissolving to obtain the lithium ion battery electrolyte. The cycling stability of the micron silicon cathode in the electrolyte is tested by adopting 325-mesh micron silicon powder as an electrode active substance (Si content accounts for 70wt% of the total mass of the electrode) and assembling a Si I Li semi-battery.
Comparative example 4
An electrolyte is prepared: adding 1mol/L lithium hexafluorophosphate into tetraethyl glycol dimethyl ether, and completely dissolving to obtain the lithium ion battery electrolyte. The cycling stability of the micron silicon cathode in the electrolyte is tested by adopting 325-mesh micron silicon powder as an electrode active substance (Si content accounts for 70wt% of the total mass of the electrode) and assembling a Si I Li semi-battery.
Comparative example 5
An electrolyte was provided for comparison: and mixing tetrahydrofuran and tetraethyl glycol dimethyl ether according to a volume ratio of 1:1, and adding 1mol/L lithium bistrifluoromethylsulfonyl imide after mixing until the lithium bistrifluoromethylsulfonyl imide is completely dissolved to obtain the lithium ion battery electrolyte. 325 mesh silicon powder is used as electrode active material (Si content is 70wt% of total electrode mass), LFP is used as positive electrode active material (surface capacity is 3.0 mAh/cm) 2 ) The Si I LFP full battery is assembled for comparing the performance of the full battery in the electrolyte.
Comparative example 6
An electrolyte was provided for comparison: mixing Ethylene Carbonate (EC) and dimethyl carbonate (DMC) according to a volume ratio of 1:1, adding 1mol/L lithium hexafluorophosphate (LiPF) 6 ) And (3) completely dissolving to obtain the lithium ion battery electrolyte. 325 mesh silicon powder is used as electrode active material (Si content is 70wt% of total electrode mass), LFP is used as positive electrode active material (surface capacity is 3.0 mAh/cm) 2 ) The Si I LFP full battery is assembled for comparing the performance of the full battery in the electrolyte.
TABLE 1
As shown in table 1, as compared with comparative examples 1 to 2, for the negative electrode containing the micro silicon powder, the specific capacity and coulombic efficiency of the battery were significantly improved when 65 to 98wt% of the ether solvent was used as the electrolyte and the lithium salt concentration was 0.1 to 3mol/L. This is probably due to the lower LUMO level and thermodynamic reduction potential of ether-based solvents (0.0-0.3V vs Li/Li + ) And limited solvation ability for Li salts, so that SEI films are preferentially formed from LiPF during the entire lithiation process 6 Reduced formation, with fewer organic components, is in sharp contrast to the mixed organic-inorganic composition of conventional SEIs. The high modulus LiF-organic double-layer interface formed in the ether electrolyte can adapt to the volume change of the alloy cathode in the circulating process, thereby improving the circulating stability of the micron alloy cathode. The synergistic effect between the mixed ether further improves the interface stability of the silicon cathode and the electrolyte.
TABLE 2
As shown in table 2, when the electrolyte was further added with a reducing additive, the specific capacity and coulombic efficiency of the battery were further improved as a result of comparison between example 5 and examples 9 and 10. This is probably due to the fact that the introduction of the additive can further improve the reduction stability of the ether electrolyte, promote the formation of firm and stable SEI, minimize the loss of active lithium, and further improve the interface stability of the negative electrode/electrolyte, thereby improving the cycle stability of the micron silicon negative electrode.
TABLE 3 Table 3
As shown in Table 3, the use of the mixed ether can effectively improve the voltage application range of the ether electrolyte and promote the application of the positive electrode materials such as LFP, LCO, NCM and the like in the ether electrolyte; on the other hand, the corrosion of HF on the anode material and the dissolution of transition metal in the electrolyte can be prevented, the structure of the anode material is stabilized, and the circulation performance of the anode material in the ether electrolyte is further improved.
TABLE 4 Table 4
As shown in table 4, the specific capacity and coulombic efficiency after cycling of the examples using the technical scheme of the present application were significantly better than those of the comparative examples. The invention is characterized in that the mixed ether can modify the interface of the cathode and stabilize the cathode of the micro alloy by introducing the additive; meanwhile, the electrolyte can be effectively formed into a film at the positive electrode, the voltage application range of the ether electrolyte is effectively improved, the structure of the positive electrode material is stabilized, the corrosion of HF on the positive electrode material and the dissolution of transition metal in the electrolyte are prevented, the circulation performance of the positive electrode material in the ether electrolyte is improved, and the electrochemical performance of the micron alloy-based lithium ion battery is obviously improved.
In summary, the invention utilizes the synergistic effect of the components to stabilize the electrode electrolyte interface by optimizing the formula of the electrolyte, widens the voltage application range of the ether-based electrolyte, improves the cycling stability of the high-capacity micro-alloy cathode material, improves the high-voltage performance of the ether-based electrolyte, and finally improves the electrochemical performance of the high-specific-energy full battery based on the micro-alloy cathode.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the invention in any way, and any person skilled in the art may make modifications or alterations to the disclosed technical content to the equivalent embodiments. However, any simple modification, equivalent variation and variation of the above embodiments according to the technical substance of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims (9)

1. The lithium ion battery electrolyte suitable for the high-capacity micro-alloy negative electrode is characterized by comprising an ether bond-containing compound and lithium salt;
the electrolyte further includes a reducing additive; the reducing additive comprises one or more of lithium borohydride or lithium hydride.
2. The lithium ion battery electrolyte suitable for the high-capacity micro-alloy negative electrode according to claim 1, wherein the mass fraction of the ether bond-containing compound in the electrolyte is 65-98%, the mass fraction of the reducing additive is 0.01-5%, and the concentration of lithium salt is 0.1-3mol/L.
3. The lithium ion battery electrolyte suitable for the high-capacity micro-alloy negative electrode according to claim 1, wherein the ether bond-containing compound comprises at least one of tetrahydrofuran, 2-methyltetrahydrofuran, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether or tetraethylene glycol dimethyl ether.
4. The lithium ion battery electrolyte suitable for high capacity micro-alloyed negative electrode according to claim 1, wherein the lithium salt comprises LiPF 6 。
5. A lithium ion battery comprising the electrolyte of any one of claims 1-4, a microalloy negative electrode, a positive electrode, and a separator.
6. The lithium ion battery of claim 5, wherein the microalloyed negative electrode comprises 50-95wt% negative electrode active material.
7. The lithium ion battery of claim 6, wherein the negative electrode active material comprises Si, sn, bi, ge, al having a particle size of 1-50 μm.
8. The lithium ion battery according to claim 5, wherein the positive electrode comprises a positive electrode active material, specifically comprising S, se, li 2 S, LFP, LCO, LMO, NCM or NCA.
9. An electronic device comprising a lithium-ion battery according to any one of claims 5-8.
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