Modified sulfide solid electrolyte and preparation method and application thereof

Abstract

The invention provides a modified sulfide solid electrolyte and a preparation method and application thereof.The modified sulfide solid electrolyte comprises lithium thioborate crystals, composite grain boundaries are contained between the lithium thioborate crystals, and lithium iodide is contained in the composite grain boundaries. The structures of crystal lattices and composite crystal boundaries in the modified sulfide solid electrolyte are stable, so that the lithium ion migration capability of the modified sulfide solid electrolyte can be improved, and the ionic conductivity of the modified sulfide solid electrolyte is obviously improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of solid-state battery materials, and relates to a modified sulfide solid electrolyte and its preparation method and application. Background Art

[0002] With the transformation of the global energy structure and the promotion of the "dual carbon" goal, electric vehicles (EVs) have become the core carriers for carbon reduction in the transportation field. However, the current mainstream lithium-ion batteries are limited by the liquid electrolyte system, facing energy density bottlenecks (<300 Wh / kg) and safety hazards (such as thermal runaway and electrolyte leakage), and it is difficult to meet the requirements of long-range, fast charging, and high safety of EVs. There is an urgent need to develop a new generation of battery technologies.

[0003] All-solid-state batteries (ASSBs) use solid electrolytes to replace liquid electrolytes, which can theoretically break through the energy density limit (>500 Wh / kg) and completely solve the flammability problem. Currently, the mainstream solid electrolytes include three major systems: oxides (such as LLZO), polymers (such as PEO), and sulfides (such as Li2S-P2S5). Among them, sulfide-based materials have become the focus of industrialization due to their ionic conductivity close to that of liquid electrolytes (10 -2 ~10 -3 S / cm). The sulfide-based solid electrolyte is represented by the Li2S-P2S5 system. In its crystal lattice, S 2- has a high polarizability, and Li + has a low migration barrier (<0.2 eV). By halogen doping (such as LiI) or oxygen substitution (Li3PS 4- x O x ), the conductivity can be further improved. However, sulfide electrolytes still face the following key problems: they are sensitive to air (H2O + Li2S → H2S↑), and strict inert atmospheres (such as Ar glove boxes) are required for preparation, increasing the manufacturing cost; side reactions (such as sulfide oxidation and increased interfacial resistance) are likely to occur when contacting with cathode materials (such as NCM), resulting in cyclic capacity attenuation; their low hardness (<2 GPa) makes it difficult to inhibit lithium dendrite penetration, affecting battery safety.

[0004] In response to the above problems, researchers have proposed various optimization schemes: (1) introducing an interfacial buffer layer (such as Li3PO4 coating on the cathode) to reduce the interfacial impedance; (2) developing composite electrolytes (sulfide + oxide / polymer) to improve the mechanical strength; (3) element doping (such as Ge and Sn substituting P) to improve air stability. However, these methods often lead to process complexity or sacrifice ionic conductivity.

[0005] CN119370812A discloses a preparation method of a pure-phase sulfide solid electrolyte, a solid electrolyte and a solid battery. The specific preparation process is as follows: First, weigh LiX, phosphorus sulfide and lithium sulfide required for synthesizing the sulfide solid electrolyte according to the molar ratio, where X is Cl, Br or I. Dissolve LiX and lithium sulfide in an alcohol solvent to obtain a mixed solution; dry the mixed solution to obtain a mixed powder of recrystallized LiX and lithium sulfide, and ball-mill the mixed powder together with phosphorus sulfide to obtain a precursor material for preparing the sulfide solid electrolyte; heat the precursor material to the temperature required for the reaction of the precursor material to obtain the pure-phase sulfide solid electrolyte Li6PS5X.

[0006] CN114649562A discloses the preparation and application of a sulfide solid electrolyte doped with group IIA elements and double halogens. The specific preparation process is as follows: Weigh pure reagents Li2S, P2S5, CaF2 and LiCl according to the stoichiometric ratio Li2S:P2S5:CaF2:LiCl = 2.25:0.45:0.1:1.3, mix them and grind them manually for 15 minutes. Put them into a zirconia ball-milling tank, add zirconia balls for ball-milling according to the mass ratio of 1:50, set the rotation speed of the ball mill to 550 rpm, and ball-mill for 17 hours. Then scrape off the sample attached to the tank wall, and manually grind it with a mortar for 15 min. After screening through a 400-mesh sieve, a uniformly mixed precursor can be obtained. Then press the tablet (diameter 12 mm) with a pressure of 350 MPa. Load it into a quartz tube and seal the tube. Heat it to 550 °C at a rate of 0.5 / min, keep it warm for 7 h, and after cooling, obtain the 5.8 P 0.0.9 Ca 0.1 S 4.5 F 0.2 X 1.3 solid electrolyte powder.

[0007] The above-mentioned schemes are all bulk doping technologies, which change the phase of the sulfide-based solid electrolyte, or part of S is replaced by halogen elements, which is likely to cause lattice distortion of the electrolyte during charge and discharge, resulting in uneven stress distribution and it is difficult to ensure the battery rate performance. Summary of the Invention

[0008] The purpose of the present invention is to provide a modified sulfide solid electrolyte, a preparation method and an application thereof. The modified sulfide solid electrolyte of the present invention contains a composite grain boundary, and the lattice and the structure of the composite grain boundary in the modified sulfide solid electrolyte are stable, which can improve the lithium ion migration ability of the modified sulfide solid electrolyte, and significantly improve the ionic conductivity of the modified sulfide solid electrolyte.

[0009] To achieve the purpose of this invention, the present invention adopts the following technical solutions:

[0010] In a first aspect, the present invention provides a modified sulfide solid electrolyte, the modified sulfide solid electrolyte comprising lithium thioborate crystals, composite grain boundaries being present between the lithium thioborate crystals, and lithium iodide being present within the composite grain boundaries.

[0011] Due to the high polarizability of S in the sulfide-based electrolyte during the charge and discharge process - and the low migration energy barrier of Li + , although it has good lithium ion migration ability, it far from meets the industrial requirements. In the modified sulfide solid electrolyte of the present invention, I - does not replace S 2- , but rather lithium iodide induces the formation of lithium thioborate Li a B b S c (hereinafter referred to as LBS) crystals, such that lithium iodide is inserted into the grain boundaries between the LBS crystals, forming an amorphous / crystalline phase of LBS and an LBS-LiI grain boundary, i.e., a composite grain boundary, thereby enhancing the lithium ion migration ability of the modified sulfide solid electrolyte and assembling a solid-state battery with excellent rate performance. The boron element in the modified sulfide solid electrolyte of the present invention is present in the crystal lattice and can change its structure, forming more vacancies and channels, thereby promoting the migration of lithium ions and increasing the ionic conductivity. Further, boron can stabilize the interface between the crystals, reduce the interface impedance, such that the crystal structure does not collapse during the process of inserting lithium iodide into the grain boundaries. The synergistic effect of boron and lithium iodide in the composite grain boundary can improve the overall ion transport performance.

[0012] Preferably, the chemical formula of the lithium thioborate crystal is Li 10 B 10 S 20 .

[0013] Preferably, in the modified sulfide solid electrolyte, the mass ratio of the lithium thioborate crystal to lithium iodide is 1:(0.15 - 0.5), for example: 1:0.15, 1:0.2, 1:0.3, 1:0.4 or 1:0.5, etc., not limited to the listed values, and other unlisted values within this numerical range are equally applicable, preferably 1:(0.25 - 0.4).

[0014] Preferably, the crystalline phase structure in the composite grain boundary comprises amorphous lithium thioborate, crystalline lithium thioborate, and a composite crystalline phase;

[0015] Preferably, the composite crystalline phase comprises lithium thioborate and LiI.

[0016] In a second aspect, the present invention provides a method for preparing the modified sulfide solid electrolyte as described in the first aspect, the preparation method comprising the following steps:

[0017] Mixing lithium sulfide, elemental boron, elemental sulfur and lithium iodide and grinding them to obtain a mixed material;

[0018] The mixed material is placed in a carrier, the carrier is placed in a closed device, and the mixed material is subjected to segmented sintering treatment by a chemical vapor deposition method to obtain the modified sulfide solid electrolyte.

[0019] The present invention adopts a method combining mechanical mixing and chemical vapor deposition, strictly controls the process, and grinds LiI and Li 10 B 10 S 20 The precursor (lithium sulfide, elemental boron, elemental sulfur) powders are fully mixed to ensure that the LiI particles are evenly distributed in the LBS matrix, providing a basis for the migration of LiI to the grain boundaries during subsequent high-temperature sintering. In addition, the mechanical energy generated by the grinding process can partially break the surface bonding of the LBS particles, forming more grain boundary defects, creating active sites for LiI enrichment at the grain boundaries. In the subsequent chemical vapor deposition (CVD), under high-temperature sintering, the decomposition temperature of LiI (~446°C) is lower than the lattice stability temperature of LBS (>600°C), resulting in LiI preferentially melting and diffusing along the LBS grain boundaries, rather than entering the lattice to replace sulfur (S 2- ). The compact structure of the LBS lattice (high Li-S bond energy) hinders the substitution reaction of I-, while the amorphous region at the grain boundary has a loose structure, and LiI precipitates in the form of crystals. The method can not only improve the ionic conductivity and mechanical strength, but also solve the problem of uneven stress distribution.

[0020] Preferably, the grinding method includes ball milling.

[0021] Preferably, the ball milling speed is 300 rpm to 500 rpm, for example, 300 rpm, 350 rpm, 400 rpm, 450 rpm or 500 rpm, etc., not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0022] Preferably, the ball milling time is 1 h to 3 h, for example, 1 h, 1.5 h, 2 h, 2.5 h or 3 h.

[0023] Preferably, the carrier comprises a boron nitride crucible.

[0024] Preferably, the sealing device comprises a sealed quartz tube.

[0025] Preferably, the atmosphere of the staged sintering process includes nitrogen.

[0026] Preferably, the environmental pressure for the segmented sintering treatment is 180 mtorr to 220 mtorr, for example: 180 mtorr, 190 mtorr, 200 mtorr, 210 mtorr or 220 mtorr, etc. It is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0027] Preferably, the segmented sintering treatment includes a first sintering treatment and a second sintering treatment carried out in sequence.

[0028] Preferably, the heating rate of the first sintering treatment is 80 °C / h to 100 °C / h, for example: 80 °C / h, 85 °C / h, 90 °C / h, 95 °C / h or 100 °C / h, etc. It is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0029] Preferably, the holding temperature of the first sintering treatment is 700 °C to 800 °C, for example: 700 °C, 720 °C, 750 °C, 780 °C or 800 °C, etc. It is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0030] Preferably, the holding time of the first sintering treatment is 1.5 h to 2.5 h, for example: 1.5 h, 1.8 h, 2 h, 2.2 h or 2.5 h, etc. It is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0031] Preferably, the cooling rate from the first sintering treatment to the second sintering treatment is 30 °C / h to 80 °C / h, for example: 30 °C / h, 40 °C / h, 50 °C / h, 60 °C / h, 70 °C / h or 80 °C / h, etc. It is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0032] Preferably, the holding temperature of the second sintering treatment is 500 °C to 600 °C, for example: 500 °C, 520 °C, 550 °C, 580 °C or 600 °C, etc. It is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0033] Preferably, the holding time of the second sintering treatment is 10 h to 15 h, for example: 10 h, 11 h, 12 h, 13 h, 14 h or 15 h, etc. It is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0034] Preferably, a cooling treatment is carried out after the segmented sintering treatment.

[0035] Preferably, the cooling rate of the cooling treatment is 40°C / h to 60°C / h. For example: 40°C / h, 45°C / h, 50°C / h, 55°C / h or 60°C / h, etc. It is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0036] In a third aspect, the present invention provides a solid-state battery, and the solid-state battery includes the modified sulfide solid electrolyte as described in the first aspect.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] (1) The modified sulfide solid electrolyte of the present invention contains composite grain boundaries, and the crystal lattice and the structure of the composite grain boundaries in the modified sulfide solid electrolyte are stable, which can improve the lithium-ion migration ability of the modified sulfide solid electrolyte, so that the ionic conductivity of the modified sulfide solid electrolyte is significantly improved.

[0039] (2) The ionic conductivity of the modified sulfide solid electrolyte of the present invention can reach 0.55×10 - 3 S / cm or more at 25°C. The capacity retention rate of the solid-state battery made thereof after 50 cycles can reach 64.2% or more. By optimizing the key process parameters, including the ratio of the LiI content, the ball-milling process parameters, the temperature and pressure control of the segmented sintering, and the chemical composition design of lithium thioborate, the ionic conductivity of the modified sulfide solid electrolyte can reach 0.85×10 -3 S / cm or more at 25°C, and the capacity retention rate of the solid-state battery made thereof after 50 cycles can reach 86.4% or more. Description of the Drawings

[0040] Figure 1 is the SEM image of the modified sulfide solid electrolyte prepared in Example 1 of the present invention.

[0041] Figure 2 is the boron EDS distribution map of the modified sulfide solid electrolyte prepared in Example 1 of the present invention.

[0042] Figure 3 is the lithium EDS distribution map of the modified sulfide solid electrolyte prepared in Example 1 of the present invention. Detailed Embodiments

[0043] The technical solutions of the present invention will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations to the present invention.

[0044] Example 1

[0045] This embodiment provides a modified sulfide solid electrolyte, which is prepared by the following method:

[0046] Weigh Li2S, B element, and S element in a molar ratio of Li:B:S of 10:10:20, add LiI accounting for 30% of the total mass of Li2S, B element, and S element, and grind them in a ball mill at a speed of 400 rpm for 2 h to obtain a mixed material;

[0047] Load the mixed material into a boron nitride crucible, seal it in a quartz tube (pressure is 200 mtorr), and sinter it in a box furnace with nitrogen gas flowing through. The specific sintering conditions are as follows: heat it up to 750 °C at a rate of 90 °C / h, hold it at 750 °C for 2 h (the first sintering), cool it down to 550 °C at a cooling rate of 50 °C / h, hold it at 550 °C for 12 h (the second sintering), and then cool it to room temperature (25 °C) at a rate of 50 °C / h. After sintering, take the quartz tube into an argon glove box and recover the modified sulfide solid electrolyte from the crucible. The chemical formula of the lithium thioborate crystal in the modified sulfide solid electrolyte is Li 10 B 10 S 20 , the mass ratio of the lithium thioborate crystal to lithium iodide is 1:0.3. The modified sulfide solid electrolyte includes lithium thioborate crystals, and there are composite grain boundaries between the lithium thioborate crystals. The crystal phase structure in the composite grain boundaries includes amorphous lithium thioborate, crystalline lithium thioborate, and a composite crystal phase composed of lithium thioborate and LiI.

[0048] The SEM image of the modified sulfide solid electrolyte is as shown in Figure 1 The EDS image of the modified sulfide solid electrolyte is as shown in Figures 2 - 3 As shown in Figures 1 - 3 It can be seen that small particles of LiI are distributed in the composite grain boundary gaps of the lithium thioborate crystals in the modified sulfide solid electrolyte of the present application.

[0049] Example 2

[0050] This embodiment provides a modified sulfide solid electrolyte, which is prepared by the following method:

[0051] Weigh Li2S, B element, and S element in a molar ratio of Li:B:S of 10:10:20, add LiI accounting for 40% of the total mass of Li2S, B element, and S element, and grind them in a ball mill at a speed of 500 rpm for 2 h to obtain a mixed material;

[0052] Load the mixed materials into a boron nitride crucible, seal it in a quartz tube (pressure is 220 mtorr), and sinter it in a box furnace with nitrogen flowing through. The specific sintering conditions are as follows: heat up at a rate of 80 °C / h to 700 °C, hold at 700 °C for 2.5 h, cool down at a rate of 50 °C / h to 500 °C, hold at 500 °C for 15 h, and then cool to room temperature (25 °C) at a rate of 40 °C / h. After sintering, bring the quartz tube into an argon glove box and recover the modified sulfide solid electrolyte from the crucible. The chemical formula of the lithium thioborate crystal in the modified sulfide solid electrolyte is Li 10 B 10 S 20 , the mass ratio of the lithium thioborate crystal to lithium iodide is 1:0.4. The modified sulfide solid electrolyte includes lithium thioborate crystals, and there are composite grain boundaries between the lithium thioborate crystals. The crystal phase structure in the composite grain boundaries includes amorphous lithium thioborate, crystalline lithium thioborate, and a composite crystal phase composed of lithium thioborate and LiI.

[0053] Example 3

[0054] This example provides a modified sulfide solid electrolyte, which is prepared by the following method:

[0055] Weigh Li2S, elemental B, and elemental S in a molar ratio of Li:B:S of 10:10:20, add LiI accounting for 50% of the total mass of Li2S, elemental B, and elemental S, and grind them in a ball mill at a speed of 300 rpm for 3 h to obtain a mixed material;

[0056] Load the mixed material into a boron nitride crucible, seal it in a quartz tube (pressure is 180 mtorr), and sinter it in a box furnace with nitrogen flowing through. The specific sintering conditions are as follows: heat up at a rate of 100 °C / h to 800 °C, hold at 800 °C for 1.5 h, cool down at a rate of 80 °C / h to 600 °C, hold at 600 °C for 10 h, and then cool to room temperature (25 °C) at a rate of 60 °C / h. After sintering, bring the quartz tube into an argon glove box and recover the modified sulfide solid electrolyte from the crucible. The chemical formula of the lithium thioborate crystal in the modified sulfide solid electrolyte is Li 10 B 10 S 20 , the mass ratio of the lithium thioborate crystal to lithium iodide is 1:0.25. The modified sulfide solid electrolyte includes lithium thioborate crystals, and there are composite grain boundaries between the lithium thioborate crystals. The crystal phase structure in the composite grain boundaries includes amorphous lithium thioborate, crystalline lithium thioborate, and a composite crystal phase composed of lithium thioborate and LiI.

[0057] Example 4

[0058] This implementation is only different from Example 1 in that LiI with a total mass of 15% of Li2S, elemental B, and elemental S is added, and the mass ratio of lithium thioborate crystal to lithium iodide is 1:0.15. Other conditions and parameters are exactly the same as those in Example 1.

[0059] Example 5

[0060] This implementation is only different from Example 1 in that LiI with a total mass of 50% of Li2S, elemental B, and elemental S is added, and the mass ratio of lithium thioborate crystal to lithium iodide is 1:0.5. Other conditions and parameters are exactly the same as those in Example 1.

[0061] Example 6

[0062] This implementation is only different from Example 1 in that the ball-milling speed is 200 rpm. Other conditions and parameters are exactly the same as those in Example 1.

[0063] Example 7

[0064] This implementation is only different from Example 1 in that the ball-milling speed is 800 rpm. Other conditions and parameters are exactly the same as those in Example 1.

[0065] Example 8

[0066] This implementation is only different from Example 1 in that the temperature of the first sintering is 750 °C. Other conditions and parameters are exactly the same as those in Example 1.

[0067] Example 9

[0068] This implementation is only different from Example 1 in that the temperature of the first sintering is 850 °C. Other conditions and parameters are exactly the same as those in Example 1.

[0069] Example 10

[0070] This implementation is only different from Example 1 in that the temperature of the second sintering is 450 °C. Other conditions and parameters are exactly the same as those in Example 1.

[0071] Example 11

[0072] This implementation is only different from Example 1 in that the temperature of the second sintering is 650 °C. Other conditions and parameters are exactly the same as those in Example 1.

[0073] Example 12

[0074] This implementation is only different from Example 1 in that the pressure inside the quartz tube is 150 mtorr. Other conditions and parameters are exactly the same as those in Example 1.

[0075] Example 13

[0076] The difference between this example and Example 1 is only that the pressure inside the quartz tube is 250 mtorr, and other conditions and parameters are exactly the same as those in Example 1.

[0077] Example 14

[0078] The difference between this example and Example 1 is only that Li 10 B 10 S 20 is replaced with lithium thioborate crystal with the chemical formula Li6B6S 10 , and other conditions and parameters are exactly the same as those in Example 1.

[0079] Comparative Example 1

[0080] This comparative example provides a solid electrolyte in which iodine replaces sulfur in thiobisulfide. The modified sulfide solid electrolyte is prepared by the following method:

[0081] Weigh Li2S, elemental B, and elemental S in a stoichiometric ratio of Li:B:S:I = 10:10:19:1, place them in a ball mill, and grind them at a speed of 400 rpm for 12 h to obtain a mixed material;

[0082] Put the mixed material into a boron nitride crucible, seal it in a quartz tube (pressure is 200 mtorr), and sinter it in a box furnace with nitrogen gas flowing through. The specific sintering conditions are: heat it up to 750 °C at a speed of 90 °C / h, hold it at 750 °C for 8 h, and cool it naturally to obtain the modified sulfide solid electrolyte Li 10 B 10 S 19 I.

[0083] Comparative Example 2

[0084] The difference between this comparative example and Example 1 is only that it is sintered only at 750 °C without staged sintering, and other conditions and parameters are exactly the same as those in Example 1.

[0085] Performance test:

[0086] (1) Test the ionic conductivity of the modified sulfide solid electrolytes prepared in the examples and comparative examples at 25 °C respectively.

[0087] (2) Mix stoichiometric Li2S, P2S5, LiCl with 50 zirconia balls (U = 10 mm) in a zirconia pot. After ball milling at a rotation speed of 500 rpm for 14 h, a Li6PS5Cl precursor is obtained. After the ball milling process, the mixture is sealed in a quartz bottle and kept under inert conditions, and annealed at 450 °C for 8 h to obtain Li6PS5Cl. Use the modified sulfide solid electrolytes prepared in the examples and comparative examples as solid electrolytes, and use LiNi 0.8Co 0.1 Mn 0.1 O2, Li6PS5Cl and carbon black additive are mixed in a ratio of 69:30:1 as the cathode material of the solid-state battery. A solid-state battery is assembled with graphite as the anode. Finally, a solid-state battery is fabricated on the electrolyte / cathode disk in a glove box filled with Ar at a pressure of 6.8 MPa. And its electrochemical performance is tested. The test results are shown in Table 1:

[0088] Table 1

[0089]

[0090]

[0091] As can be seen from Table 1, from Examples 1-14, it can be obtained that the ionic conductivity of the modified sulfide solid electrolyte of the present invention can reach 0.55×10 -3 S / cm or more at 25°C. The capacity retention rate of the fabricated solid-state battery after 50 cycles can reach 64.2% or more. By optimizing the key process parameters, including the ratio of LiI content, ball milling process parameters, temperature and pressure control of segmented sintering, and the chemical composition design of lithium thioborate, the ionic conductivity of the modified sulfide solid electrolyte can reach 0.85×10 -3 S / cm or more at 25°C. The capacity retention rate of the fabricated solid-state battery after 50 cycles can reach 86.4% or more. The present invention has successfully developed a high-performance modified sulfide solid electrolyte. Due to the synergistic effect of the directional distribution of LiI at the grain boundaries and the lattice stability of boron element, the problems of interfacial side reactions and uneven stress distribution in traditional sulfide electrolytes are effectively solved. It significantly improves the ionic transport efficiency and structural stability of the material, providing important technical support for the development of solid-state batteries with high energy density and long cycle life.

[0092] From the comparison between Example 1 and Examples 4-5, it can be obtained that in the modified sulfide solid electrolyte of the present invention, the content of lithium iodide affects its structure and performance. Controlling the mass ratio of lithium thioborate crystal to lithium iodide at 1:(0.25 - 0.4), the performance of the modified sulfide solid electrolyte is better. If the content of lithium iodide is too high, the grain boundary structure is too dense, hindering the lithium ion transport path. If the content of lithium iodide is too low, the distribution of LiI at the grain boundaries is sparse, unable to form a continuous lithium ion transport channel. In addition, the grain boundaries lack LiI filling, resulting in uneven stress distribution and easy generation of cracks.

[0093] Comparing Example 1 with Examples 6 - 7, it can be seen that during the preparation process of the modified sulfide solid electrolyte of the present invention, the ball - milling speed affects its structure and performance. Controlling the ball - milling speed within 300 rpm to 500 rpm results in better performance of the prepared modified sulfide solid electrolyte. If the ball - milling speed is too fast, excessive mechanical energy is input, damaging the LBS crystal structure, significantly increasing the proportion of the amorphous phase, reducing the mechanical strength of the material, and hindering Li⁺ migration; if the ball - milling speed is too slow, it causes insufficient or excessive LiI content in local areas of the sintered material, and the grain - boundary modification effect is poor.

[0094] Comparing Example 1 with Examples 8 - 9, it can be seen that during the preparation process of the modified sulfide solid electrolyte of the present invention, the temperature of the first sintering affects its structure and performance. Controlling the temperature of the first sintering within 700 °C to 800 °C results in better performance of the prepared modified sulfide solid electrolyte. If the temperature of the first sintering is too high, part of the lattice melts, and LiI at the grain boundary enters the bulk phase, triggering phase separation; if the temperature of the first sintering is too low, LiI is not fully melted and cannot be evenly distributed at the grain boundary, forming a discontinuous transport channel.

[0095] Comparing Example 1 with Examples 10 - 11, it can be seen that during the preparation process of the modified sulfide solid electrolyte of the present invention, the temperature of the second sintering affects its structure and performance. Controlling the temperature of the second sintering within 500 °C to 600 °C results in better performance of the prepared modified sulfide solid electrolyte. If the temperature of the second sintering is too high, the volatilization of LiI is aggravated at high temperature, and part of it reacts with LBS to form an unstable phase; if the temperature of the second sintering is too low, it leads to insufficient crystallization of LBS and an increase in the proportion of the amorphous region.

[0096] Comparing Example 1 with Examples 12 - 13, it can be seen that during the preparation process of the modified sulfide solid electrolyte of the present invention, the pressure of the sintering treatment affects its structure and performance. Controlling the pressure of the sintering treatment within 180 mtorr to 220 mtorr results in better performance of the prepared modified sulfide solid electrolyte. If the pressure of the sintering treatment is too high, the LBS grains are crushed, reducing the mechanical strength; if the pressure of the sintering treatment is too low, it causes insufficient contact between particles, a significant increase in the porosity of the material, a decrease in ionic conductivity, a reduction in the contact area between the electrode and the electrolyte, and an increase in the interfacial resistance.

[0097] Comparing Example 1 with Example 14, it can be seen that the type of lithium thioborate crystal in the modified sulfide solid electrolyte of the present invention affects its performance. In the lattice of Li 10 B 10 S 20 , a higher molar ratio of boron (B) and sulfur (S) (B:S = 1:2) forms denser lithium vacancies and more continuous ion - transport channels. While Li6B6S 10(B:S = 1:1.67) The relatively low boron ratio in the lattice results in restricted lithium-ion migration paths and a decrease in ionic conductivity.

[0098] Comparing Example 1 with Comparative Example 1, it can be seen that iodine substituting sulfur easily causes lattice distortion of the electrolyte during charge and discharge, leading to uneven stress distribution and making it difficult to ensure the rate performance of the battery. In the modified sulfide solid electrolyte of the present invention, I - does not substitute S 2- , but lithium iodide induces the formation of Li a B b S c (hereinafter referred to as LBS) crystals, enabling lithium iodide to insert into the grain boundaries between LBS crystals, forming the amorphous / crystalline phase of LBS and the LBS-LiI grain boundary, i.e., the composite grain boundary, thereby enhancing the lithium-ion migration ability of the modified sulfide solid electrolyte and assembling a solid-state battery with excellent rate performance.

[0099] Comparing Example 1 with Comparative Example 2, it can be seen that the segmented sintering process realizes the optimized growth of LBS grains, the grain boundary oriented distribution of LiI, and material densification by precisely controlling the temperature gradient and holding time, thereby significantly enhancing the ionic conductivity, mechanical strength, and cycling stability. Canceling the second sintering stage will result in the failure of grain boundary modification, an increase in structural defects, and an aggravation of interfacial side reactions, seriously affecting the comprehensive performance of the solid electrolyte.

[0100] The applicant declares that the above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A modified sulfide solid electrolyte, characterized in that, The modified sulfide solid electrolyte includes lithium thioborate crystals, and there are composite grain boundaries between the lithium thioborate crystals, and lithium iodide is contained in the composite grain boundaries.

2. The modified sulfide solid electrolyte according to claim 1, characterized in that, The chemical formula of the lithium thioborate crystal is Li 10 B 10 S 20 ; Preferably, in the modified sulfide solid electrolyte, the mass ratio of lithium thioborate crystals to lithium iodide is 1:(0.15 - 0.5), preferably 1:(0.25 - 0.4).

3. The modified sulfide solid electrolyte according to claim 1 or 2, characterized in that, The crystal phase structure in the composite grain boundaries includes amorphous lithium thioborate, crystalline lithium thioborate and a composite crystal phase; Preferably, the composite crystal phase includes lithium thioborate and LiI.

4. A method for preparing a modified sulfide solid electrolyte according to any one of claims 1-3, characterized in that, The preparation method includes the following steps: Mix lithium sulfide, elemental boron, elemental sulfur and lithium iodide and grind them to obtain a mixed material; Place the mixed material in a carrier, place the carrier in a closed device, and perform segmented sintering treatment on the mixed material by chemical vapor deposition to obtain the modified sulfide solid electrolyte.

5. The preparation method according to claim 4, characterized in that, The grinding method includes ball milling; Preferably, the speed of the ball milling is 300 rpm - 500 rpm; Preferably, the time of the ball milling is 1 h - 3 h.

6. The preparation method according to claim 4 or 5, characterized in that, The carrier includes a boron nitride crucible; Preferably, the closed device includes a sealed quartz tube.

7. The preparation method according to any one of claims 4-6, characterized in that, The atmosphere of the segmented sintering treatment includes nitrogen; Preferably, the ambient pressure of the segmented sintering treatment is 180 mtorr - 220 mtorr.

8. The preparation method according to any one of claims 4-7, characterized in that, The segmented sintering treatment includes a first sintering treatment and a second sintering treatment carried out in sequence; Preferably, the heating rate of the first sintering treatment is 80 °C / h - 100 °C / h; Preferably, the holding temperature of the first sintering treatment is 700 °C - 800 °C; Preferably, the holding time of the first sintering treatment is 1.5 h - 2.5 h; Preferably, the cooling rate from the first sintering treatment to the second sintering treatment is 30 °C / h - 80 °C / h; Preferably, the holding temperature of the second sintering treatment is 500 °C - 600 °C; Preferably, the holding time of the second sintering treatment is 10 h - 15 h.

9. The preparation method according to any one of claims 4-8, characterized in that, Cooling treatment is carried out after the segmented sintering treatment; Preferably, the cooling rate of the cooling treatment is 40 °C / h - 60 °C / h.

10. A solid-state battery, characterized in that, The solid-state battery includes the modified sulfide solid electrolyte according to any one of claims 1 - 3.

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