Preparation method of lithium phosphorus sulfur bromine solid electrolyte

Abstract

The invention discloses a preparation method of a lithium-phosphorus-sulfur-bromine solid-state electrolyte, and relates to the technical field of solid-state lithium batteries. The material is subjected to raw material pretreatment, mechanochemical ball milling, high-temperature crystallization treatment and post-treatment processes, so that the solid electrolyte with high crystallinity, high ionic conductivity and good processability is obtained. According to the method, dynamic bromine atmosphere control is adopted, sulfur partial pressure adjustment and particle size gradient design are combined, and the structural stability and the ion transmission performance of the material are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of solid-state lithium batteries, and in particular to a preparation method of a lithium phosphorus sulfur bromine solid electrolyte. Background Art

[0002] In recent years, with the rapid development of electric vehicles, wearable devices and energy storage systems, the demand for secondary batteries with high energy density, high safety and long life has been increasing. However, traditional liquid lithium-ion batteries have serious safety hazards due to the flammability, leakage of the liquid electrolyte and the short-circuit risk caused by the growth of lithium dendrites. All-Solid-State Lithium Batteries (ASSLBs) are considered to be an ideal technical solution for next-generation high-performance lithium batteries because they use solid electrolytes to replace traditional liquid electrolytes, which can effectively improve the safety of the batteries and have a wider electrochemical stability window and higher energy density.

[0003] In the solid electrolyte system, sulfide-based solid electrolytes have received extensive attention due to their high room-temperature ionic conductivity (up to 10 -3 ~10 -2 S / cm), low interfacial impedance, and excellent electrochemical stability. Among them, the lithium phosphorus sulfur bromine (Li 3 PS 4 Br) system with an argyrodite structure is a typical sulfide solid electrolyte material, which shows great application potential in the field of all-solid-state lithium batteries due to its high ionic conductivity, good chemical stability and low interfacial impedance.

[0004] At present, the preparation of sulfide solid electrolytes mainly adopts processes such as mechanochemical method, solid-phase sintering method, melt quenching method and solution synthesis method. Among them, the mechanochemical method is widely used in the preparation of Li 3 PS 4 Br and related sulfide electrolyte materials because of its relatively simple process and easy large-scale production. However, the existing technology still has the following limitations:

[0005] Problems of bromine element loss and lattice defects: During the high-temperature sintering process, bromides (such as LiBr) are volatile, resulting in unstable Br- content in the final product, affecting the lattice structure and ionic conductivity of the material. Due to the volatilization of bromine, defect phases may be formed in the material, resulting in limited local ion transport and reducing the overall performance of the electrolyte.

[0006] Problems of particle distribution and filling performance of materials: In traditional preparation processes, it is difficult to precisely control the particle size of particles. Usually, the obtained powder particles have a wide size distribution, which affects the filling and densification degree of the electrolyte in the battery. Excessively large particles may lead to poor interfacial contact between the electrolyte and the electrode, while excessively small particles are prone to agglomeration, reducing the processability of the powder.

[0007] Problems of interfacial compatibility and electrochemical stability: Sulfide solid electrolytes may undergo interfacial reactions with cathode materials under high voltages, resulting in an increase in interfacial impedance and affecting the long-cycle performance of the battery. Existing interfacial modification technologies (such as ion doping or composite electrolytes) still have room for optimization, especially in improving the long-term stability and cycle life of materials. Summary of the Invention

[0008] In view of the above technical bottlenecks, the present invention provides an optimized preparation process based on dynamic Br 2 atmosphere compensation, gradient particle size design, and surface modification technology to improve the ionic conductivity, stability, and batch consistency of Li 3 PS 4 Br solid electrolytes.

[0009] The specific solutions are as follows:

[0010] A preparation method of a lithium phosphorus sulfur bromine solid electrolyte, characterized by comprising the following steps:

[0011] (1) Raw material pretreatment:

[0012] The raw materials, by mass, are: 45 - 55 parts of Li 2 S, 15 - 20 parts of P 2 S 5 15 - 20 parts, 25 - 35 parts of S, and 5 - 10 parts of LiBr; Li 2 S is vacuum dried at 100 - 120 °C for 12 - 16 h in an argon glove box to remove surface LiOH / Li 2 CO 3 ; the remaining raw materials are crushed and screened to a particle size of ≤50 μm under an argon atmosphere;

[0013] (2) Mechanochemical ball milling:

[0014] Under the protection of an inert atmosphere, the raw materials are fed in a molar ratio of Li:S:P:Br = 3:4:1:1, and an additional 5% excess of Li 2 S is added; ball milling is carried out using a planetary ball mill with a ball-to-material ratio of 35 - 40:1;

[0015] (3) High-temperature crystallization treatment:

[0016] Encapsulated with a vacuum quartz tube; Stepwise temperature rise sintering: Raise the temperature to 180 - 220 °C at a rate of 1 °C / min and hold for 2 h; Raise the temperature to 500 - 550 °C at a rate of 3 - 5 °C / min and hold for 8 - 12 h to form the argyrodite phase; Naturally cool to 250 - 350 °C and then quench; During the reaction process, use dynamic Br 2 atmosphere to compensate for Br volatilization, and use S / Li 2 S mixed buffer to stabilize the sulfur partial pressure;

[0017] (4) Post-treatment process:

[0018] Secondary ball milling, with the ball milling medium being an ionic liquid solvent, controlling the particle size ≤ 20 μm; Coating with a 2 - 5 nm thick Li 3 PO 4 layer.

[0019] Furthermore, the ball milling conditions during the mechanochemical ball milling process: Argon protection, rotation speed 400 - 600 rpm, alternating forward and reverse rotation, and reversing every 10 min.

[0020] Furthermore, the ball milling during the mechanochemical ball milling process is carried out in stages:

[0021] Rough grinding for 1.5 - 2.5 h to break up agglomerates;

[0022] Main grinding for 15 - 25 h to form an amorphous precursor;

[0023] Fine grinding for 1 - 3 h to optimize the particle morphology.

[0024] Furthermore, the encapsulation pressure of the vacuum quartz tube during the high-temperature crystallization process is not higher than 10 -3 Pa.

[0025] Furthermore, the Br 2 atmosphere pressure during the high-temperature crystallization process is 0.1 - 0.3 atm.

[0026] Furthermore, the method for adjusting the sulfur partial pressure during the high-temperature crystallization process is to add 1 - 3 wt% S / Li 2 S mixed buffer.

[0027] Furthermore, the specific process conditions for depositing Li 3 PO 4 during the post-treatment process are: Reaction temperature 250 - 400 °C, deposition time 30 - 120 min; Using POCl 3 vapor phase hydrolysis method to generate Li 3 PO 4 coating film.

[0028] Furthermore, the synthesis method of the ionic liquid solvent is:

[0029] By weight, 100 - 130 parts of hexane, 1 - 4 parts of 1 - allyl - 3 - butylimidazolium bis(trifluoromethanesulfonyl)imide (CAS: 863498 - 34 - 4), 5 - 8 parts of mercapto - β - cyclodextrin (CAS: 81644 - 55 - 5), 1 - 3 parts of ethylenediamine are stirred at 60 - 70 °C for 8 - 12 h to obtain an ionic liquid solvent.

[0030] Mercapto - allyl addition reaction mechanism

[0031] Free radical initiation: Under the condition of 60 - 70 °C, the nitrogen - hydrogen bond in ethylenediamine may homolytically cleave to generate amino radicals. The amino radicals abstract hydrogen atoms from the mercapto groups of mercapto - β - cyclodextrin to form sulfur radicals, thus initiating the reaction.

[0032] Addition and chain process: The generated sulfur radicals attack the allyl double bond of 1 - allyl - 3 - butylimidazolium bis(trifluoromethanesulfonyl)imide to form a carbon radical intermediate. This intermediate abstracts hydrogen atoms from other mercapto - β - cyclodextrin to achieve chain growth, and the reaction terminates when the free radicals combine with each other.

[0033] Improving the performance of ionic liquid and electrolyte: The ionic liquid solvent formed by the addition reaction has good solubility and dispersibility, and high thermal stability. It can make the lithium phosphorus sulfur bromine solid electrolyte uniformly disperse and the particle size controllable during secondary ball milling, and also increase the specific surface area of the electrolyte, improving the ionic conduction performance.

[0034] Optimizing the process and expanding the application: The efficient ionic liquid solvent improves the efficiency of secondary ball milling, reduces energy consumption and process uncertainty, and ensures the stable product quality. Its designability provides more choices for the preparation process and expands the application scope of solid electrolytes in the battery field.

[0035] Technical effects

[0036] 1) Improving the stability of bromine content and reducing lattice defects: By adopting a dynamic Br2 atmosphere, compensating for Br volatilization during the high - temperature sintering process, and at the same time cooperating with an S / Li2S buffer to control the sulfur partial pressure.

[0037] 2) Improving the ionic conductivity of the material: By adopting high - temperature sintering + Br2 compensation + graded ball milling, improving the crystallinity of the material and optimizing the particle size distribution to improve the ionic transport efficiency.

[0038] 3) Enhancing the antioxidant stability of the material and extending its service life: By using chemical vapor deposition (CVD) to deposit a 2 - 5 nm thick Li 3 PO 4 protective layer on the surface of the material to improve the antioxidant ability. Specific embodiments

[0039] The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited to these specific embodiments. Those skilled in the art should recognize that the present invention covers all alternative solutions, improvement solutions, and equivalent solutions that may be included within the scope of the claims.

[0040] Example 1

[0041] (1) Raw material pretreatment

[0042] Weigh according to the mass parts: Li 2 S 50 g, P 2 S 5 18 g, S 30 g, LiBr 7 g.

[0043] In an argon glove box, Li 2 S is vacuum dried at 110 °C for 14 h to remove the surface LiOH / Li 2 CO 3 .

[0044] The remaining raw materials are crushed and screened to a particle size of ≤40 μm under an argon atmosphere.

[0045] (2) Mechanochemical ball milling

[0046] Under argon protection, feed materials according to the molar ratio of Li:S:P:Br = 3:4:1:1, and additionally add 5% excess Li 2 S.

[0047] Use a planetary ball mill for ball milling, with a ball-to-material ratio of 38:1. The ball milling parameters are as follows:

[0048] Coarse grinding: 2 h (400 rpm, alternating forward and reverse, reversing every 10 min);

[0049] Main grinding: 20 h (500 rpm);

[0050] Fine grinding: 2 h (600 rpm, optimizing the particle morphology).

[0051] (3) High-temperature crystallization treatment

[0052] Use a vacuum quartz tube for encapsulation, with a vacuum pressure of ≤10 -3 Pa.

[0053] Stepwise heating:

[0054] Heat up to 200 °C at a rate of 1 °C / min and hold for 2 h;

[0055] Heat up to 520 °C at a rate of 4 °C / min and hold for 10 h to form the argyrodite phase;

[0056] Use Br 2Atmosphere compensation, pressure controlled at 0.2 atm, and 2 wt% S / Li 2 mixed buffer agent was added.

[0057] After the reaction was completed, it was naturally cooled to 300 °C and then rapidly quenched.

[0058] (4) Post-treatment process

[0059] Secondary ball milling was carried out using an ionic liquid solvent to control the powder particle size ≤ 15 μm.

[0060] Synthesis method of the ionic liquid solvent in this example: 100 g of hexane, 1 g of 1-allyl-3-butylimidazolium bis(trifluoromethanesulfonyl)imide (CAS: 863498-34-4), 5 g of mercapto-β-cyclodextrin (CAS: 81644-55-5), 1 g of ethylenediamine were stirred at 60 °C for 12 h to obtain the ionic liquid solvent.

[0061] Using chemical vapor deposition, Li was deposited at 300 °C with a thickness of 2 nm 3 PO 4 , deposition time 60 min, POCl 3 Gas-phase hydrolysis to generate Li 3 PO 4 .

[0062] Example 2

[0063] (1) Raw material pretreatment

[0064] Weigh according to the mass parts: Li 2 S 55 g, P 2 S 5 16 g, S 28 g, LiBr 6 g.

[0065] In an argon glove box, Li 2 S was vacuum dried at 100 °C for 12 h.

[0066] The remaining raw materials were crushed and screened to a particle size ≤ 50 μm in an argon environment.

[0067] (2) Mechanochemical ball milling

[0068] Charge according to the molar ratio of Li:S:P:Br = 3:4:1:1, and additionally add 5% excess Li 2 S.

[0069] Using a planetary ball mill, the ball-to-material ratio is 40:1, and the ball milling parameters are as follows:

[0070] Coarse grinding: 2.5 h (450 rpm, forward and reverse rotation alternately, changing direction every 10 min);

[0071] Primary grinding: 18 h (550 rpm);

[0072] Fine grinding: 1.5 h (600 rpm).

[0073] (3) High-temperature crystallization treatment

[0074] Vacuum packaging pressure ≤ 10 -3 Pa.

[0075] Stepwise temperature increase:

[0076] Heat up to 190 °C at 1 °C / min and hold for 2 h;

[0077] Heat up to 530 °C at 3 °C / min and hold for 9 h;

[0078] Use Br 2 Atmosphere compensation (0.1 atm), and add 3 wt% S / Li 2 S mixed buffer.

[0079] Cool naturally to 250 °C and then quench rapidly.

[0080] (4) Post-treatment process

[0081] Perform secondary ball milling with an ionic liquid solvent to control the powder particle size ≤ 18 μm.

[0082] Synthesis method of the ionic liquid solvent in this example: Mix 110 g of hexane, 2 g of 1-allyl-3-butylimidazolium bis(trifluoromethanesulfonyl)imide (CAS: 863498-34-4), 6.5 g of mercapto-β-cyclodextrin (CAS: 81644-55-5), and 2 g of ethylenediamine, stir at 65 °C for 10 h to obtain the ionic liquid solvent.

[0083] Use chemical vapor deposition to deposit 3 nm thick Li 3 PO 4 for 90 min at 280 °C.

[0084] Example 3

[0085] (1) Raw material pretreatment

[0086] Weigh according to the mass parts: Li 2 S 47 g, P 2 S 5 20 g, S 32 g, LiBr 8 g.

[0087] Carry out vacuum drying of Li 2 S at 120 °C for 16 h in an argon glove box.

[0088] Crush and screen the remaining raw materials to a particle size ≤ 45 μm in an argon environment.

[0089] (2) Mechanochemical ball milling

[0090] Charge materials according to the molar ratio of Li:S:P:Br = 3:4:1:1, and additionally add 5% excess Li 2 S.

[0091] Use a planetary ball mill with a ball-to-material ratio of 36:1. The ball milling parameters are as follows:

[0092] Coarse grinding: 1.5 h (420 rpm, alternating forward and reverse rotation, changing direction every 10 min);

[0093] Main grinding: 22 h (520 rpm);

[0094] Fine grinding: 1.5 h (600 rpm).

[0095] (3) High-temperature crystallization treatment

[0096] Vacuum packaging pressure ≤ 10 -3 Pa.

[0097] Stepwise temperature increase:

[0098] Increase the temperature to 220 °C at a rate of 1 °C / min and hold for 2 h;

[0099] Increase the temperature to 550 °C at a rate of 5 °C / min and hold for 8 h;

[0100] Use Br 2 atmosphere compensation (0.3 atm), and add 1 wt% S / Li 2 S mixed buffer.

[0101] Cool naturally to 350 °C and then quench rapidly.

[0102] (4) Post-treatment process

[0103] Perform secondary ball milling using an ionic liquid solvent to control the powder particle size ≤ 12 μm.

[0104] Synthesis method of the ionic liquid solvent in this example: Mix 120 g of hexane, 3 g of 1-allyl-3-butylimidazolium bis(trifluoromethanesulfonyl)imide (CAS: 863498-34-4), 7 g of mercapto-β-cyclodextrin (CAS: 81644-55-5), and 2 g of ethylenediamine, stir at 65 °C for 10 h to obtain the ionic liquid solvent.

[0105] Use chemical vapor deposition to deposit 5 nm thick Li 3 PO 4 for 120 min at 400 °C.

[0106] Example 4

[0107] (1) Raw material pretreatment

[0108] Weigh according to mass parts: Li 2 S 52 g, P 2 S 5 17 g, S 27 g, LiBr 9 g.

[0109] In an argon glove box, vacuum-dry Li 2 S at 105 °C for 13 h.

[0110] The remaining raw materials are crushed and screened to a particle size of ≤42 μm under an argon atmosphere.

[0111] (2) Mechanochemical ball milling

[0112] Charge according to the molar ratio of Li:S:P:Br = 3:4:1:1, and additionally add 5% excess Li 2 S.

[0113] Use a planetary ball mill with a ball-to-material ratio of 37:1, and the ball milling parameters are as follows:

[0114] Coarse grinding: 2 h (430 rpm, alternating forward and reverse, changing direction every 10 min);

[0115] Main grinding: 19 h (510 rpm);

[0116] Fine grinding: 2 h (600 rpm).

[0117] (3) High-temperature crystallization treatment

[0118] Vacuum packaging pressure ≤ 10 -3 Pa.

[0119] Stepwise temperature increase:

[0120] Increase the temperature to 210 °C at a rate of 1 °C / min and hold for 2 h;

[0121] Increase the temperature to 540 °C at a rate of 4 °C / min and hold for 10 h;

[0122] Use Br 2 Atmosphere compensation (0.15 atm), and add 2 wt% S / Li 2 S mixed buffer.

[0123] (4) Post-treatment process

[0124] Perform secondary ball milling using an ionic liquid solvent to control the powder particle size ≤ 17 μm.

[0125] Synthesis method of the ionic liquid solvent in this example: 130 g of hexane, 4 g of 1-allyl-3-butylimidazolium bis(trifluoromethanesulfonyl)imide (CAS: 863498-34-4), 8 g of mercapto-β-cyclodextrin (CAS: 81644-55-5), and 3 g of ethylenediamine were stirred at 70 °C for 8 h to obtain the ionic liquid solvent.

[0126] Using chemical vapor deposition, Li was deposited at 350 °C with a thickness of 4 nm 3 PO 4 , and the deposition time was 80 min.

[0127] Comparative Example 1

[0128] The difference from Example 1 is only that an equal amount of hexane was used to replace the ionic liquid solvent for secondary ball milling.

[0129] Comparative Example 2

[0130] The difference from Example 1 is only that 1-allyl-3-butylimidazolium bis(trifluoromethanesulfonyl)imide was not added during the preparation of the ionic liquid solvent.

[0131] Comparative Example 3

[0132] The difference from Example 1 is only that mercapto-β-cyclodextrin was not added during the preparation of the ionic liquid solvent.

[0133] The testing methods related to the present invention are as follows:

[0134] 1. Ionic conductivity test

[0135] Testing method: Using alternating current impedance spectroscopy (EIS), the test frequency range is 1 mHz–1 MHz, the test temperature is 25 °C, and an Au electrode is used to optimize the electrode / electrolyte interface contact.

[0136] 2. Antioxidant property (XPS analysis):

[0137] Testing method: The surface composition was measured after the sample was exposed to an environment with a humidity of 50% RH for 72 h.

[0138] 3. Cycle stability test

[0139] Testing method: Using a LiFePO 4 / LPSBr / Li full cell, the charge-discharge rate is 0.1C, the test temperature is 25 °C, and the capacity retention rate of 100 cycles is recorded.

[0140] The test results are as follows:

[0141]

[0142] In summary, the technical solution of the present invention is superior to the comparative example in terms of ionic conductivity, antioxidant property, and cycle stability, and is suitable for the industrial application of high-performance all-solid-state lithium batteries.

[0143] Although the specific embodiments of the present invention have been described in detail, those of ordinary skill in the art can implement variations of the embodiments. In addition, such variations can be obtained without departing from the true spirit and scope of the present invention as described in the appended claims.

Claims

1. A method for preparing a lithium phosphorus sulfur bromine solid electrolyte, characterized in that: The following steps are involved: (1) Raw material pretreatment: The raw materials are calculated by weight: Li2S 45-55 parts, P2S5 15-20 parts, S25-35 parts, LiBr 5-10 parts; Li2S is vacuum dried at 100-120°C for 12-16 hours in an argon glove box to remove surface LiOH / Li2CO3; the remaining raw materials are crushed and sieved to a particle size of ≤50μm under an argon environment; (2) Mechanochemical ball milling: Under the protection of an inert atmosphere, the raw materials were fed in a molar ratio of Li:S:P:Br=3:4:1:1, and 5% excess Li2S was additionally added; ball milling was performed using a planetary ball mill with a ball-to-material ratio of 35-40:1; (3) High temperature crystallization treatment: The method is to use a vacuum quartz tube for packaging; perform step-by-step temperature sintering: 1°C / min to 180-220°C and keep the temperature for 2 hours; 3-5°C / min to 500-550°C and keep the temperature for 8-12 hours to form a argyrodite phase; naturally cool to 250-350°C and then quench; during the reaction, a dynamic Br2 atmosphere is used to compensate for Br volatilization, and a S / Li2S mixed buffer is used to stabilize the sulfur partial pressure; (4) Post-processing process: Secondary ball milling, the ball milling medium is ionic liquid solvent, and the particle size is controlled to be ≤20μm; a 2-5nm thick Li3PO4 layer is coated by vapor deposition method; The ionic liquid solvent is prepared by reacting 1-allyl-3-butyl imidazole bis(trifluoromethanesulfonyl)imide salt and mercapto-β-cyclodextrin.

2. The method for preparing a lithium phosphorus sulfur bromine solid electrolyte according to claim 1, characterized in that: The ball milling conditions during the mechanochemical ball milling process are as follows: argon protection, a rotation speed of 400-600 rpm, alternating forward and reverse rotations, and reversing every 10 minutes.

3. The method for preparing a lithium phosphorus sulfur bromine solid electrolyte according to claim 1, characterized in that: The mechanochemical ball milling process is carried out in stages: Coarse grinding for 1.5-2.5h to break up agglomerates; Main grinding for 15-25h to form an amorphous precursor; Fine grinding was performed for 1-3 h to optimize particle morphology.

4. The method for preparing a lithium phosphorus sulfur bromine solid electrolyte according to claim 1, characterized in that: The vacuum quartz tube packaging pressure during the high temperature crystallization process is not higher than 10 -3 Pa.

5. The method for preparing a lithium phosphorus sulfur bromide solid electrolyte according to claim 1, characterized in that: The Br2 atmosphere pressure during the high temperature crystallization process is 0.1-0.3atm.

6. The method for preparing a lithium phosphorus sulfur bromide solid electrolyte according to claim 1, characterized in that: The sulfur partial pressure is adjusted during the high temperature crystallization process by adding 1-3 wt % S / Li2S mixed buffer.

7. The method for preparing a lithium phosphorus sulfur bromide solid electrolyte according to claim 1, characterized in that: The specific process conditions for vapor deposition of Li3PO4 in the post-treatment process are: reaction temperature 250-400°C, deposition time 30-120min; and Li3PO4 coating is generated by POCl3 vapor phase hydrolysis method.

8. The method for preparing a lithium phosphorus sulfur bromide solid electrolyte according to claim 1, characterized in that: The synthesis method of the ionic liquid solvent is: By weight, 100-130 parts of hexane, 1-4 parts of 1-allyl-3-butylimidazole bis(trifluoromethanesulfonyl)imide salt, 5-8 parts of mercapto-β-cyclodextrin, and 1-3 parts of ethylenediamine are stirred at 60-70° C. for 8-12 hours to obtain an ionic liquid solvent.

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