Electrolyte solvation structure with thermal stability, electrolyte and preparation method

Abstract

The invention discloses an electrolyte solvation structure with thermal stability, an electrolyte and a preparation method, and relates to the technical field of high-energy density batteries, the electrolyte solvation structure comprises metal cations, solvent molecules, salt anions and an additive; wherein the solvent molecules comprise cyclic carbonate and / or chain carbonate; the salt anions comprise at least one of the following ions: hexafluorophosphate ions, bis (fluorosulfonyl) imide radicals, bis (trifluorosulfonyl) imide radicals, perchlorate radicals, tetrafluoroborate radicals, bis (oxalato) borate radicals and difluoro (oxalato) borate radicals; the additive comprises at least one of fluoroethylene carbonate, vinylene carbonate, ethylene sulfate, propylene sulfite and difluorophosphate radical; and the total coordination number of the metal cations is 3-5. According to the invention, the technical problem that thermal runaway is easy to occur in the traditional carbonic ester-based electrolyte is relieved.

Description

Technical Field

[0001] The invention relates to the technical field of high energy density batteries, and in particular to an electrolyte solvation structure with thermal stability, an electrolyte and a preparation method. Background Art

[0002] In modern society, lithium-ion batteries are widely used in various portable electronic devices, electric vehicles, and energy storage systems due to their high energy density and long cycle life. However, with the increasing demand for higher energy density, the safety issues of lithium-ion batteries have become increasingly prominent. High energy density lithium-ion batteries may cause the battery to be more susceptible to thermal runaway under various abuse conditions, thereby causing thermal disasters. Therefore, improving the safety of lithium-ion batteries has become a focus of current research. As an important component of lithium-ion batteries, the performance of the electrolyte directly affects the safety of the battery. Traditional carbonate-based electrolytes not only participate in the heat release during the heat accumulation stage inside the battery, but also provide the main fuel for fire and explosion during thermal runaway of the battery. Therefore, the development of safe electrolytes has become one of the key ways to solve the safety problems of lithium-ion batteries. Summary of the invention

[0003] In order to solve the above technical problems existing in the prior art, the embodiments of the present invention provide a thermally stable electrolyte solvation structure, electrolyte and preparation method. The technical solution is as follows:

[0004] On the one hand, a thermally stable electrolyte solvation structure is provided, comprising: metal cations, solvent molecules, salt anions and additives; wherein the solvent molecules include cyclic carbonates and / or chain carbonates; the salt anions include at least one of the following: hexafluorophosphate ion, bisfluorosulfonyl imide, bistrifluorosulfonyl imide, perchlorate, tetrafluoroborate, bisoxalatoborate, difluorooxalatoborate; the additives include at least one of the following: fluoroethylene carbonate, vinylene carbonate, vinyl sulfate, propylene sulfite, difluorophosphate; the total coordination number of the metal cations is 3-5.

[0005] Optionally, the metal cation includes any one of the following: lithium ion, sodium ion, potassium ion.

[0006] Optionally, the cyclic carbonate includes at least one of the following: ethylene carbonate, propylene carbonate; the chain carbonate includes at least one of the following: dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate.

[0007] Optionally, the coordination number of the solvent molecules in the electrolyte solvation structure is 1-2.

[0008] Optionally, the coordination number of the salt anion in the electrolyte solvation structure is 2-3.

[0009] Optionally, the coordination number of the additive in the electrolyte solvation structure is 0-1.

[0010] On the other hand, an electrolyte is also provided, comprising a solvent corresponding to the solvent molecules in the thermally stable electrolyte solvation structure provided by the present invention, a salt corresponding to the salt anion, the additive and a highly fluorinated diluent that does not participate in actual coordination.

[0011] Optionally, the high-fluorinated diluent includes at least one of the following: 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 2,2,2-trifluoroethyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether.

[0012] Optionally, the content of the solvent in the electrolyte is 30-60wt.%, the content of the salt in the electrolyte is 10-25wt.%, the content of the additive in the electrolyte is 0-10wt.%, and the content of the high-fluorinated diluent in the electrolyte is 10-40wt.%.

[0013] On the other hand, a method for preparing an electrolyte is also provided, comprising: adding the electrolyte salt corresponding to the salt to a mixed organic solvent, stirring sufficiently for 0.5-1.5 hours to obtain a first solution; adding the additive to the first solution, stirring sufficiently for 5-15 minutes to obtain a second solution; adding the highly fluorinated diluent to the second solution, stirring sufficiently for 5-15 minutes to obtain the electrolyte.

[0014] The embodiments of the present invention provide a thermally stable electrolyte solvation structure, an electrolyte, and a preparation method, wherein the electrolyte solvation structure can maintain high coordination of metal cations to salt anions, thereby having a lower electron affinity and a lower reduction potential, thereby significantly reducing its overall thermochemical reactivity, inhibiting exothermic side reactions under thermal abuse, improving overall safety, and alleviating the technical problem of traditional carbonate-based electrolytes being prone to thermal runaway. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0016] Figure 1is a flow chart of a method for preparing an electrolyte provided by an embodiment of the present invention;

[0017] Figure 2 It is a schematic diagram of the equilibrium configuration of various embodiments and comparative electrolytes provided by the embodiments of the present invention after Forcite molecular dynamics;

[0018] Figure 3 It is a schematic diagram of the analysis results of radial distribution functions of solvation structures of various embodiments and comparative examples provided in the embodiments of the present invention;

[0019] Figure 4 It is a schematic diagram of the analysis results of the coordination numbers of the solvation structures of various embodiments provided in the embodiments of the present invention;

[0020] Figure 5 It is a schematic diagram of the MSD analysis results of the solvation structures of various embodiments provided in the embodiments of the present invention;

[0021] Figure 6 is a schematic diagram of a typical solvation structure with a coordination number of 4 in various embodiments provided in the embodiments of the present invention;

[0022] Figure 7 Schematic diagram of LUMO and HOMO distribution of typical solvation structures in various embodiments provided in the embodiments of the present invention;

[0023] Figure 8 The thermal abuse test temperature change curve diagram of Example 4 provided in the embodiment of the present invention and the photos before and after the test;

[0024] Fig. 9 It is a temperature variation curve diagram of a thermal abuse test of a comparative example provided in an embodiment of the present invention and photos before and after the test. DETAILED DESCRIPTION

[0025] The technical solution of the present invention is described below in conjunction with the accompanying drawings.

[0026] In the embodiments of the present invention, words such as "exemplarily" and "for example" are used to indicate examples, illustrations or explanations. Any embodiment or design described as "example" in the present invention should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Specifically, the use of the word "example" is intended to present the concept in a specific way. In addition, in the embodiments of the present invention, the meaning expressed by "and / or" can be both, or it can be either of the two.

[0027] In order to make the technical problems, technical solutions and advantages to be solved by the present invention more clear, a detailed description will be given below with reference to the accompanying drawings and specific embodiments.

[0028] The present invention provides an electrolyte solvation structure with thermal stability, comprising: metal cations, solvent molecules, salt anions and additives; wherein the additives include additive molecules and / or additive ions.

[0029] Specifically, the solvent molecules include cyclic carbonates and / or chain carbonates;

[0030] The salt anion includes at least one of the following: hexafluorophosphate ion (PF6-), bis(fluorosulfonyl imide) (FSI-), bis(trifluorosulfonyl imide) (TFSI-), perchlorate (ClO4-), tetrafluoroborate (BF4-), bis(oxalatoborate) (BOB-), difluorooxalatoborate (DFOB-);

[0031] The additive includes at least one of the following: fluoroethylene carbonate (FEC), vinylene carbonate (VC), diethylene sulfate (DTD), diethylene sulfite (ES), difluorophosphate (PO2F2-);

[0032] The total coordination number of the metal cation is 3-5.

[0033] Preferably, the metal cation includes any one of the following: lithium ion (Li+), sodium ion (Na+), potassium ion (K+).

[0034] Preferably, the cyclic carbonate includes at least one of the following: ethylene carbonate (EC), propylene carbonate (PC);

[0035] The chain carbonate includes at least one of the following: dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC).

[0036] Preferably, the coordination number of the solvent molecules in the electrolyte solvation structure is 1-2.

[0037] Preferably, the coordination number of the salt anion in the electrolyte solvation structure is 2-3.

[0038] Preferably, the coordination number of the additive in the electrolyte solvation structure is 0-1.

[0039] The present invention also provides an electrolyte, comprising a solvent corresponding to the solvent molecules in the solvation structure of the thermally stable electrolyte provided by an embodiment of the present invention, a salt corresponding to the salt anion, an additive, and a highly fluorinated diluent that does not participate in the actual coordination.

[0040] The electrolyte provided in the embodiment of the present invention adds a highly fluorinated diluent to the basic components of the traditional electrolyte, which can reduce the overall solvation capacity of the solvent molecules and spontaneously allow more anions to enter the solvation sheath of the metal cations, thereby forming a highly stable solvation structure.

[0041] Specifically, the diluent is an organic liquid that cannot dissolve lithium salts and is believed not to participate in coordination, but can play a role in modifying the solvation structure composition, increasing ion mobility and improving the electrochemical window of the electrolyte.

[0042] In an optional embodiment provided in an embodiment of the present invention, the highly fluorinated diluent includes at least one of the following: 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (HFE), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), 2,2,2-trifluoroethyl ether (BTFE), 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether (OTE).

[0043] Preferably, the content of the solvent in the electrolyte is 30-60wt.%, the content of the salt in the electrolyte is 10-25wt.%, the content of the additive in the electrolyte is 0-10wt.%, and the content of the high-fluorinated diluent in the electrolyte is 10-40wt.%.

[0044] Figure 1 FIG. 1 is a flow chart of a method for preparing an electrolyte according to an embodiment of the present invention. Figure 1 As shown, the method specifically comprises the following steps:

[0045] Step S102, adding the electrolyte salt corresponding to the salt into the mixed organic solvent, and stirring for 0.5-1.5 hours to obtain a first solution;

[0046] Step S104, adding the additive to the first solution and stirring for 5-15 minutes to obtain a second solution;

[0047] Step S106, adding a highly fluorinated diluent into the second solution, and stirring thoroughly for 5-15 minutes to obtain an electrolyte.

[0048] In order to study the electronic structure of the molecules in the electrolyte provided by the embodiment of the present invention and the chemical activity of the solvation structure, the embodiment of the present invention uses the DMol3 module in the Materials Studio software to calculate the electronic structure, optimize the molecules and the Li+ solvation structure, and set the energy convergence to 1x10 -6 , the maximum force is 0.002Ha / A, and the maximum displacement is 0.005A; the functional is GGA-PBE, the electron treatment in the system is calculated using all-electron, the basis set is set to DNP, the basis set file version is 4.4, and the SCF self-consistent iteration convergence index is 1x10 -6 ;The smearing parameter is 0.005 Ha.

[0049] Specifically, Materials Studio software was used to build various molecular and ionic systems, certain components were set, and Amorphous Cell was used to build an amorphous system. In order to allow the molecules to disperse and the entire system to have more free volume, the initial density was set to 0.8 g / cm 3 ; Then, the Forcite Plus module was used to optimize the geometry of each system to obtain a better structure. The force field was COMPASSIII, the optimization method was Smart, the electrostatic summation method was PPPM, and the van der Waals energy summation method was Atom based; finally, the optimized model was subjected to molecular dynamics simulation, the ensemble was NPT, the pressure was one atmosphere, the pressure control method was Berendsen; the temperature was set to 400 K, and the temperature control method was NHL; the total simulation time was 500 ps, ​​the time step was 1 fs, and one frame was output every 1000 steps. The force field and non-bonded energy summation method were consistent with the optimization parameters.

[0050] Specifically, the present invention provides the following five different components of electrolyte for simulation calculation:

[0051] Embodiment 1:

[0052] Calculation and simulation parameters: The molar ratio of each component of the electrolyte is LiFSI:DMC:TTE=10:20.77:37.62; the total number of molecules in the molecular dynamics simulation is 5132;

[0053] Preparation of electrolyte: In a high-purity argon gas atmosphere glove box, 1.5 g LiFSI, 1.5 g DMC, and 7 g TTE were uniformly mixed for 1-1.5 h to form 10 g of uniform electrolyte solution.

[0054] Embodiment 2:

[0055] Calculation and simulation parameters: The molar ratio of each component of the electrolyte LiFSI:DMC:TTE=10:31.15:16.12; the total number of molecules in the molecular dynamics simulation is 6110;

[0056] Preparation of electrolyte: In a high-purity argon gas atmosphere glove box, 3g LiFSI, 3g DMC, and 4g TTE were uniformly mixed for 1-1.5h to form 10g of uniform electrolyte solution.

[0057] Embodiment 3:

[0058] Calculation and simulation parameters: The molar ratio of each component of the electrolyte is LiFSI:DMC:TTE=10:34.61:0; the total number of molecules in the molecular dynamics simulation is 5152;

[0059] Preparation of electrolyte: In a high-purity argon gas atmosphere glove box, 5 g LiFSI and 5 g DMC were uniformly mixed for 1-1.5 h to form 10 g of uniform electrolyte solution.

[0060] Embodiment 4:

[0061] Calculation and simulation parameters: The molar ratio of each component of the electrolyte is LiFSI:DMC:TTE=10:69.23:18.81; the total number of molecules in the molecular dynamics simulation is 6344;

[0062] Preparation of electrolyte: In a high-purity argon gas atmosphere glove box, 1.5 g LiFSI, 5 g DMC, and 3.5 g TTE were uniformly mixed for 1-1.5 h to form 10 g of uniform electrolyte solution.

[0063] Comparative Example:

[0064] Calculation and simulation parameters: The molar ratio of each component of the electrolyte is LiPF6:EC:DMC=10:44.14:64.43; the total number of molecules in the molecular dynamics simulation is 7764;

[0065] Electrolyte preparation: Commercial lithium-ion battery electrolyte 1MLiPF6inEC:DMC (3:7 by vol) was obtained from commercial sources.

[0066] Finally, the obtained trajectory file is analyzed. The energy, density, temperature and other curves can be used to determine whether the model is balanced, and the trajectory of the final equilibrium stage is analyzed; the solvation structure of Li+ and the number of coordinated molecules are obtained through RDF; the diffusion and migration properties of Li+ are obtained through MSD; and the interaction energy of Li+ in the entire system and the adsorption energy between Li+ and individual molecules and ions are calculated at the same time, in order to better study the competitive adsorption of solvated structure molecules.

[0067] The following tests were conducted on lithium-ion batteries injected with the electrolytes in the above-mentioned Example 4 and the comparative example. With reference to the national standard "GB38031-2020" battery thermal safety test method, a more stringent 200°C thermal abuse (heating) test was conducted on high energy density 1Ah NCM811|Gr soft-pack lithium-ion battery, proving that the electrolyte in Example 4 has better safety performance under thermal abuse, and ultimately proving that the thermally stable solvation structure in the electrolyte plays a key role in inhibiting thermal failure under actual thermal abuse scenarios. The specific experimental steps are:

[0068] 1) Place two groups of fully charged batteries flat in a hot box, with the upper layer being Example 4 and the lower layer being the comparative example, without a fixture, and take photos for record;

[0069] 2) Connect the thermocouple at the geometric center of the front of the battery and the positive and negative electrodes of the battery to detect the temperature and voltage changes during the battery heating process, and add another thermocouple to record the ambient temperature of the hot box;

[0070] 3) Turn on the power of the hot box and set the heating program. The temperature rise rate of the hot box is 5℃ / min, the temperature of the hot box rises from room temperature to 200℃, and the temperature is kept for 60 minutes. The test stop condition is the completion of the program;

[0071] 4) After the test, take out the tested batteries, take photos, and put them into a ziplock bag.

[0072] The specific analysis results are as follows: Figure 2-Figure 9 As shown in Table 1-Table 3. Among them, Figure 2 is a schematic diagram of equilibrium configurations of various embodiments and comparative electrolytes provided according to embodiments of the present invention after Forcite molecular dynamics, Figure 3 is a schematic diagram of the analysis results of the radial distribution function of the solvation structure of various embodiments and comparative examples provided according to the embodiments of the present invention, Figure 4 is a schematic diagram of the coordination number analysis results of the solvation structures of various embodiments provided in accordance with the embodiments of the present invention, Figure 5 is a schematic diagram of the MSD analysis results of the solvation structures of various embodiments provided in accordance with the embodiments of the present invention, Figure 6 is a schematic diagram of a typical solvation structure with a coordination number of 4 in various embodiments provided in accordance with an embodiment of the present invention, Figure 7 is a schematic diagram of LUMO and HOMO distribution of typical solvation structures in various embodiments provided according to the embodiments of the present invention, Figure 8 is a temperature change curve diagram of the thermal abuse test of Example 4 provided according to an embodiment of the present invention and photos before and after the test, Fig. 9 The following are temperature change curves of thermal abuse test of comparative examples provided in the embodiments of the present invention and photos before and after the test. Table 1 shows the average coordination number analysis results of solvent structures of various embodiments and comparative examples provided in the embodiments of the present invention, Table 2 shows the energy analysis results of various solvation structures in various embodiments provided in the embodiments of the present invention, and Table 3 shows the thermal abuse (heating) test results.

[0073] Table 1 Average coordination number analysis results of solvent structures of various embodiments and comparative examples

[0074]

[0075] Table 2 Energy analysis results of various solvation structures in various embodiments

[0076]

[0077] Table 3 Thermal abuse (heating) test results

[0078]

[0079] The embodiments of the present invention provide a thermally stable electrolyte solvation structure, electrolyte and preparation method, which have the following technical effects compared with the prior art:

[0080] 1. Improve the thermal stability of the electrolyte: Since the solvation structure designed in the present invention has lower electron affinity and reduction potential, the chemical stability of the electrolyte under high temperature conditions is enhanced. This effectively inhibits the exothermic side reactions under thermal abuse, reduces the risk of thermal runaway, and thus improves the overall safety of the battery.

[0081] 2. Enhance the overall safety of the battery: By optimizing the solvation structure, the side reactions between the electrolyte and the electrode materials are reduced. This not only prolongs the service life of the battery, but also significantly improves the safety performance of the battery under extreme conditions.

[0082] 3. Optimize electrochemical performance: Highly coordinated lithium salt anions help form a stable solid electrolyte interface (SEI) film, improving the cycle stability and electrochemical performance of the battery.

[0083] 4. Reduce the incidence of gas-generating side reactions: By inhibiting unnecessary reduction reactions, the decomposition of the electrolyte and gas generation are reduced. This not only improves the safety of the battery, but also reduces the accumulation of internal pressure in the battery, further improving the reliability of the battery.

[0084] It should be understood that in various embodiments of the present invention, the size of the serial numbers of the above-mentioned processes does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0085] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A thermally stable electrolyte solvation structure, characterized in that: include: Metal cations, solvent molecules, salt anions and additives; among them, The solvent molecules include cyclic carbonates and / or chain carbonates; The salt anion includes at least one of the following: hexafluorophosphate ion, bisfluorosulfonyl imide ion, bistrifluorosulfonyl imide ion, perchlorate ion, tetrafluoroborate ion, bisoxalate borate ion, difluorooxalate borate ion; The additive comprises at least one of the following: fluoroethylene carbonate, vinylene carbonate, vinyl sulfate, propylene sulfite, difluorophosphate; The total coordination number of the metal cation is 3-5.

2. The thermally stable electrolyte solvation structure according to claim 1, characterized in that: The metal cation includes any one of the following: lithium ion, sodium ion, potassium ion.

3. The thermally stable electrolyte solvation structure according to claim 1, characterized in that: The cyclic carbonate includes at least one of the following: ethylene carbonate, propylene carbonate; The chain carbonate includes at least one of the following: dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate.

4. The thermally stable electrolyte solvation structure according to claim 1, characterized in that: The coordination number of the solvent molecules in the electrolyte solvation structure is 1-2.

5. The thermally stable electrolyte solvation structure according to claim 1, characterized in that: The coordination number of the salt anion in the electrolyte solvation structure is 2-3.

6. The thermally stable electrolyte solvation structure according to claim 1, characterized in that: The coordination number of the additive in the electrolyte solvation structure is 0-1.

7. An electrolyte, characterized in that: The invention comprises a solvent corresponding to the solvent molecule in the solvation structure of the thermally stable electrolyte as claimed in claim 1, a salt corresponding to the salt anion, the additive and a highly fluorinated diluent not participating in the actual coordination.

8. The electrolyte according to claim 7, characterized in that The highly fluorinated diluent includes at least one of the following: 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 2,2,2-trifluoroethyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether.

9. The electrolyte according to claim 7, characterized in that The content of the solvent in the electrolyte is 30-60wt.%, the content of the salt in the electrolyte is 10-25wt.%, the content of the additive in the electrolyte is 0-10wt.%, and the content of the high-fluorinated diluent in the electrolyte is 10-40wt.%.

10. A method for preparing the electrolyte according to claim 7, characterized in that: include: Adding the electrolyte salt corresponding to the salt into the mixed organic solvent, stirring thoroughly for 0.5-1.5h to obtain a first solution; Adding the additive to the first solution and stirring thoroughly for 5-15 minutes to obtain a second solution; The highly fluorinated diluent is added into the second solution and stirred for 5-15 minutes to obtain the electrolyte.

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