Preparation Method and Application of a Sulfide Solid Electrolyte

Abstract

The present invention discloses a preparation method and application of a sulfide solid electrolyte material. The electrolyte has a Li6PS5Cl-type structure, and its chemical general formula is Li6Nb 1‑a P a S5X(0

Description

Technical Field

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

[0002] In recent years, lithium-ion batteries have developed rapidly due to their advantages such as high energy density and long service life. However, their components inevitably contain organic electrolytes, and organic electrolytes have serious safety hazards. Inorganic solid electrolytes with better safety performance are a feasible method to improve battery safety. Classified according to the types of anions in inorganic solid electrolyte materials, oxide solid electrolytes and sulfide solid electrolytes have relatively good prospects. Compared with oxide solid electrolytes, sulfide solid electrolytes have a smaller electronegativity of sulfur ions and a lower binding force on cations; at the same time, sulfur ions have a larger radius, which is beneficial to the migration of lithium ions. Therefore, the ionic conductivity of oxide solid electrolytes is lower than that of sulfide solid electrolytes.

[0003] Patent CN 113839086 A discloses a sulfide solid electrolyte, its preparation method, a solid electrolyte sheet, and a solid-state battery. The components of the sulfide solid electrolyte are Li 6-x PS 5-x M x+1 ; where M is a halogen element, and 0.1 < x < 0.8. However, the sulfide solid electrolytes reported in the past have low conductivity. For example, the best conductivity mentioned in Patent CN113839086A just reaches 3.98×10 -3 S / cm. Moreover, there are many problems such as low full-cell capacity and poor cycle efficiency. These problems have hindered the development of sulfide solid-state batteries. Summary of the Invention

[0004] In view of this, the present invention discloses a preparation method and application of a sulfide solid electrolyte. This electrolyte has a Li6PS5Cl-type structure, and its chemical general formula is Li6Nb 1-a P a S5X(0 < a < 1)(0 < a < 1, X = halogen). The sulfide solid electrolyte material of the present invention uses Nb to replace the P position. Through the design of the doping ratio of niobium elements, the prepared niobium element-doped sulfide solid electrolyte has high ionic conductivity, high full-cell charge-discharge specific capacity, good cycle efficiency, greatly reduced cost, and is stable to Li series negative electrodes, etc.

[0005] The technical solutions provided by the present invention are as follows:

[0006] <First Aspect>

[0007] The present invention provides a sulfide solid electrolyte with a general formula: Li6Nb 1-a P a S5X, where X is one or more of F, Cl, Br, and I.

[0008] Furthermore, the Li source includes one or more of Li2S and Li2S2.

[0009] Furthermore, the S source includes one or more of S, P2S5, P4S9, P4S3, Li2S, and Li2S2.

[0010] Furthermore, the Nb source includes one or more of NbF5, NbCl5, NbBr5, and NbI5.

[0011] Furthermore, the P source includes one or more of P, P2S5, P4S9, P4S3, P4S6, and P4S5.

[0012] Furthermore, the X source includes one or more of LiF, LiCl, LiBr, and LiI.

[0013] <Second aspect>

[0014] The present invention also provides a method for preparing the sulfide solid electrolyte described above, including the following steps:

[0015] S1: Mix the raw materials and perform ball milling to obtain an initial sulfide solid electrolyte powder. The rotation speed of the ball milling is 380 - 650 rpm, and the ball milling time is 17 - 60 h;

[0016] S2: Press the initial solid electrolyte powder obtained in step S1 at 300 - 900 MPa to obtain an initial sulfide solid electrolyte sheet;

[0017] S3: Calcinate the initial solid electrolyte sheet obtained in step S2 at a calcination temperature of 350 - 650 °C for a calcination time of 7 - 48 h to obtain the sulfide solid electrolyte.

[0018] <Third aspect>

[0019] The present invention also provides a all - solid - state battery and a preparation method thereof including the sulfide solid electrolyte described above.

[0020] The preparation method of the all - solid - state battery described above includes the following steps:

[0021] Step 1, mix the cathode material, conductive carbon material, and the sulfide solid electrolyte, and grind them evenly to obtain a cathode active material powder;

[0022] Step 2, dispersing the positive electrode active material powder in a polyvinylidene fluoride-N-methylpyrrolidone solution, stirring evenly and coating the solution on an aluminum foil to obtain a positive electrode sheet;

[0023] Step 3, pressing the sulfide solid electrolyte to obtain a solid electrolyte sheet used for assembling a battery, wherein the thickness of the electrolyte sheet is controlled to be 100-500 μm;

[0024] Step 4, place the positive electrode sheet of step 2 on one side of the solid electrolyte sheet of step 3 and press it, and finally attach lithium foil to the other side of the solid electrolyte to press it into an all-solid-state battery.

[0025] The structure of the all-solid-state battery is a sandwich structure.

[0026] The positive electrode material includes LiCoO2, LiFePO4, LiNi x CoyMn 1-x-y O2, LiNi x CoyAl 1-x-y O2, LiNi 0.5 Mn 1.5 O4, LiFe x Mn 1-x One or more of PO4.

[0027] The present invention forms a novel solid electrolyte by doping niobium element and halogen element into a traditional sulfide solid electrolyte.

[0028] Preferably, the thickness of the sandwich structure all-solid-state battery is 300-800 μm.

[0029] The key point of this application is that the prepared sulfide solid electrolyte is applied to the positive electrode of the all-solid-state battery by designing the doping ratio of the niobium element and doping with halogens; by designing the doping ratio of the niobium element and co-doping with halogens, rather than single halogen doping, the all-solid-state battery based on the sulfide solid electrolyte has high capacity, high ionic conductivity and excellent cycle retention rate.

[0030] The present invention has been found in research that only with a specific niobium doping ratio can the prepared sulfide solid electrolyte be applied to the positive electrode of an all-solid-state battery, and ensure the high capacity, high ionic conductivity, and excellent cycle retention rate of the all-solid-state battery. If the niobium content is too high, it will affect the formation of the sulfide solid electrolyte crystal phase and cause the impedance of the sulfide solid electrolyte to increase, thereby affecting the ionic conductivity of the target electrolyte and the full battery cycle performance. If the niobium content is too low, the purpose of niobium doping cannot be achieved, and the best all-solid-state battery capacity, ionic conductivity, and cycle retention rate cannot be obtained. Compared with the prior art, the present invention has the following gain effects:

[0031] (1) By designing the doping ratio of niobium element, the prepared niobium-doped sulfide solid electrolyte has high ionic conductivity and greatly reduced cost, which is beneficial to large-scale industrial production.

[0032] (2) Applying the prepared electrolyte to all-solid-state batteries improves the cycle stability of the batteries.

[0033] (3) Applying the prepared sulfide solid electrolyte to the positive electrode of all-solid-state batteries improves the battery performance BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments read in conjunction with the accompanying drawings:

[0035] Figure 1 XRD pattern of Example 1;

[0036] Figure 2 Impedance diagram of the all-solid-state battery assembled with the electrolytes prepared in Example 1 and Comparative Example 1;

[0037] Figure 3 Charge-discharge capacity diagram of the all-solid-state battery assembled with the electrolytes prepared in Example 1 and Comparative Example 1. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0038] The present invention will be described in detail below with reference to the embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that those of ordinary skill in the art can make several adjustments and improvements without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0039] Example 1

[0040] This example relates to the preparation of Li6P 0.8 Nb 0.2 S5Cl sulfide solid electrolyte and its all-solid-state battery, including the following steps:

[0041] (1) Take Li2S, P2S5, and NbCl5 with a stoichiometric ratio of Li2S:P2S5:NbCl5 = 3:0.4:0.2, mix them and perform high-energy planetary ball milling. The rotation speed of the high-energy planetary ball milling is 550 rpm, and the ball milling time is 48 h to obtain the initial solid electrolyte powder;

[0042] (2) Place 40 mg of the initial solid electrolyte powder obtained in step (1) in a tablet press mold with a diameter of 12 mm and press it into an initial solid electrolyte tablet at 600 MPa;

[0043] (3) The initial solid-state electrolyte sheet obtained in step (2) is placed in a quartz tube under an inert gas atmosphere in a glove box and vacuum sealed (~10 -5 ), and heat-treated at 550 °C for 7 h in a muffle furnace to obtain the target sulfide solid-state electrolyte material;

[0044] (4) Take 110 mg of the target sulfide solid-state electrolyte material obtained in step (3), mix it with 48 mg of lithium iron phosphate and 20 mg of VGCF, and grind them evenly to obtain the positive electrode powder; Disperse 500 mg of the positive electrode powder in a polyvinylidene fluoride-N-methylpyrrolidone solution with a mass concentration of 4%, stir magnetically until evenly mixed, and coat it on an aluminum foil to obtain an electrode sheet;

[0045] (5) The target sulfide solid-state electrolyte obtained in step (3) is placed in a tablet press mold and pressed into a solid-state electrolyte sheet about 200 microns thick. Then, place the positive electrode sheet on one side of the solid-state electrolyte and apply pressure to press it, and attach a lithium foil to the other side to press it into a all-solid-state battery.

[0046] Example 2

[0047] This example relates to the preparation of Li 6.5 P 0.9 Nb 0.1 S 5.5 Cl 0.5 sulfide solid-state electrolyte and its all-solid-state battery, including the following steps:

[0048] (1) Take Li2S, P2S5, and NbCl5 with a stoichiometric ratio of Li2S:P2S5:NbCl5 = 3.25:0.45:0.1, mix them and perform high-energy planetary ball milling. The rotation speed and time of the high-energy planetary ball milling are 550 rpm and 48 h, respectively, to obtain the initial solid-state electrolyte;

[0049] (2) Place 40 mg of the initial solid-state electrolyte powder obtained in step (1) in a tablet press mold with a diameter of 12 mm and press it into an initial solid-state electrolyte sheet at 600 MPa;

[0050] (3) Place the initial solid-state electrolyte sheet obtained in step (2) in a quartz tube under an inert gas atmosphere and vacuum seal it (~10 -5 ), and heat-treat it at 550 °C for 7 h in a muffle furnace to obtain the target sulfide solid-state electrolyte material;

[0051] (4) Take 110 mg of the target sulfide solid-state electrolyte material obtained in step (3), mix it with 48 mg of lithium iron phosphate and 20 mg of VGCF, and grind them evenly to obtain the positive electrode powder; Disperse 500 mg of the positive electrode powder in a polyvinylidene fluoride-N-methylpyrrolidone solution with a mass concentration of 5%, stir magnetically until evenly mixed, and coat it on an aluminum foil to obtain an electrode sheet;

[0052] (5) The target sulfide solid electrolyte obtained in step (4) places the material powder of the sulfide dielectric in a tablet pressing mold, presses it into a solid electrolyte sheet about 200 microns thick, then places the positive electrode sheet on one side of the solid electrolyte and presses it, and attaches an aluminum foil on the other side to make a all-solid-state battery.

[0053] Comparative Example 1

[0054] This comparative example relates to the preparation of Li6PS5Cl sulfide solid electrolyte and its all-solid-state battery, including the following steps:

[0055] (1) Take Li2S, P2S5, and LiCl with a stoichiometric ratio of Li2S:P2S5:LiCl = 5:1:2, mix them and perform high-energy planetary ball milling. The rotation speed and time of the high-energy planetary ball milling are 550 rpm and 48 h respectively, so as to obtain an initial solid electrolyte.

[0056] (2) Place 40 mg of the powder obtained in step (1) in a tablet pressing mold with a diameter of 12 mm, and press it into an initial solid electrolyte sheet at 600 MPa.

[0057] (3) Put the initial solid electrolyte sheet obtained in step (2) into a quartz tube under an inert gas atmosphere, and vacuum seal the tube (~10 -5 ), and heat-treat it at 550 °C for 7 h to obtain the target sulfide solid electrolyte material;

[0058] (4) Take 110 mg of the target sulfide solid electrolyte material obtained in step (3), mix 48 mg of lithium iron phosphate and 20 mg of VGCF, and grind them evenly to obtain the positive electrode powder. Put 500 mg of the positive electrode powder into a 4% polyvinylidene fluoride-N-methylpyrrolidone solution, stir it evenly with a magnetic stirrer and then coat it on the aluminum foil;

[0059] (5) Place the material powder of the sulfide dielectric of the target sulfide solid electrolyte obtained in step (3) in a tablet pressing mold, press it into a solid electrolyte sheet about 200 microns thick, then place the positive electrode sheet on one side of the solid electrolyte and press it, and attach an aluminum foil on the other side to make a all-solid-state battery.

[0060] Performance Test

[0061] 1. Charge and Discharge Capacity Test

[0062] Perform charge and discharge capacity tests on the batteries prepared in Example 1 and Comparative Example 1 at 1.0 C, the charge and discharge interval is 2 V - 4.2 V, and the test temperature is room temperature at 25 °C.

[0063] The results are as Figure 3As shown, the results indicate that both the cyclic stability performance and the capacity performance of the sulfide solid electrolyte doped with niobium element have been greatly improved.

[0064] 2. XRD Test

[0065] The sulfide solid electrolyte prepared in Example 1 was subjected to XRD test. Before the test, it was ground evenly, and the test range was 20° - 80° in 2θ.

[0066] The results are as Figure 1 shown, and the results show that the target crystalline sulfide solid electrolyte material was obtained by using the method mentioned in the present invention.

[0067] 3. Impedance Test

[0068] The batteries prepared in Example 1 and Comparative Example 1 were subjected to impedance test. The test range was from 0.1 Hz to 1 MHz, and the temperature was room temperature. The results show that the ionic conductivity of the sulfide solid electrolyte doped with niobium element has been improved.

[0069] The all-solid-state batteries prepared from the above Example 1 and Comparative Example 1 (the positive electrode is a mixture of lithium iron phosphate and the target electrolyte, 5 mg, NCM811:electrolyte = 3:1. The negative electrode is Li foil. The electrolyte is the example electrolyte) were installed in a special battery test device in a glove box to test the battery performance. At the same time, the assembled battery was subjected to 1.0C constant current battery charge and discharge test. The charge and discharge interval was 2V - 4.2V, and the test temperature was room temperature in a 25°C environment. The charge and discharge capacity performance is as Figure 3 shown, with a relatively high charge and discharge capacity (140 mAh / g).

[0070] The sulfide solid electrolyte prepared in Example 1 was subjected to XRD test, and the test results are as Figure 1 shown. Figure 2 is the EIS impedance diagram of the sulfide solid electrolytes prepared in Example 1 and Comparative Example 1. As can be seen from Figure 2 it, the obtained solid electrolyte has a relatively high conductivity (1.2×10 -2 S / cm).

[0071] In summary, the present invention prepares a sulfide solid electrolyte based on LPSC-type sulfide solid electrolyte with high ionic conductivity and excellent cyclic efficiency for all-solid-state battery performance.

[0072] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various deformations or modifications within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A sulfide solid electrolyte, characterized in that, The chemical formula of the sulfide solid electrolyte is Li6P 0.8 Nb 0.2 S5Cl; the sulfide solid electrolyte is obtained by the method of the following steps; S1: Mix the raw materials and perform ball milling to obtain the initial sulfide solid electrolyte powder. The rotation speed of the ball milling is 380 - 650 rpm, and the ball milling time is 17 - 60 h. S2: Press the initial solid electrolyte powder obtained in step S1 at 300 - 900 MPa to obtain the initial sulfide solid electrolyte sheet. S3: Calcinate the initial solid electrolyte sheet obtained in step S2 at a calcination temperature of 350 - 650 °C for 7 - 48 h to obtain the sulfide solid electrolyte.

2. A all - solid - state battery comprising the sulfide solid electrolyte according to claim 1.

3. A method for preparing an all-solid-state battery as claimed in claim 2, characterized in that, It includes the following steps: Step 1, mix the cathode material, conductive carbon material and the sulfide solid electrolyte, and grind them evenly to obtain the cathode active material powder. Step 2, disperse the cathode active material powder in a 4 - 5% polyvinylidene fluoride - N - methylpyrrolidone solution, stir evenly and coat it on the aluminum foil to prepare the cathode sheet. Step 3, press the sulfide solid electrolyte to obtain the solid electrolyte sheet used for assembling the battery, and the thickness of the electrolyte sheet is controlled at 100 - 500 μm. Step 4, place the cathode sheet in step 2 on one side of the solid electrolyte sheet in step 3 and press it under pressure, and finally attach a lithium foil to the other side of the solid electrolyte to press - form the all - solid - state battery.

4. The preparation method of the all-solid-state battery according to claim 3, characterized in that, The positive electrode material includes LiCoO 2， LiFePO4, LiNi 0 .5 Mn 1.5 O4, or one or more of them.

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