Oxyhalide, preparation method therefor and all-solid-state lithium battery

Abstract

The present invention provides an oxyhalide, a preparation method therefor, and an all-solid-state lithium battery. The preparation method comprises: (1) grinding a mixture of a lithium source and a boron source, which are weighed in a stoichiometric ratio, tableting the mixture, then putting the tableted mixture into a reaction tube, evacuating the reaction tube to establish a vacuum, sealing the reaction tube, and then performing primary calcination, wherein the primary calcination temperature is 300-450ºC, and the primary calcination time is 4-20 h; and (2) after the primary calcination, cooling to room temperature, taking out the intermediate product from the reaction tube, grinding and tableting the intermediate product, then putting the tableted product into a reaction tube, evacuating the reaction tube to establish a vacuum, sealing the reaction tube, performing secondary calcination, and then cooling to room temperature. The preparation method of the present invention is simple and has high raw material utilization rate and no byproducts, thereby facilitating industrial production. The prepared oxyhalide has relatively high ionic conductivity and stability, and relatively good interface stability with metal lithium. The prepared all-solid-state lithium battery has excellent electrochemical performance.

Description

Oxyhalide, preparation method thereof and all-solid-state lithium battery TECHNICAL FIELD

[0001] The present application relates to an oxyhalide, a preparation method thereof and an all-solid-state lithium battery. BACKGROUND

[0002] All-solid-state lithium batteries are attracting attention due to their simple structure, high safety and large energy density. Since all-solid-state lithium batteries use a solid electrolyte instead of an electrolyte and a separator, the battery is thinner and smaller in volume, thereby improving the energy density of the battery and the safety performance of the battery. Therefore, it is of great significance to develop an all-solid-state lithium battery that can replace traditional lithium ion batteries. However, all-solid-state lithium batteries face the following problems: (1) on the electrode layer, how to meet the transmission problem of positive and negative electrodes and electrolyte ions; (2) the positive and negative electrodes cannot maintain very good contact during the cycle process; (3) lithium dendrites are easily generated during the charging and discharging process of metal lithium, which leads to poor electrochemical performance of all-solid-state lithium batteries, which is not conducive to their practical application and development.

[0003] The core part of all-solid-state lithium batteries is a compound as a solid-state electrolyte. Currently, both organic and inorganic compounds have been reported to be good electrolytes. Compared with organic solid-state electrolytes, inorganic solid-state electrolytes have higher ionic conductivity and stability. So far, inorganic solid-state electrolyte materials can be divided into sulfides, oxides and halides. Sulfide solid electrolytes have high ionic conductivity (>10 -3 S·cm -1 ), but are easily affected by moisture in the surrounding atmosphere, causing harmful hydrolysis reactions and a serious decrease in ionic conductivity; in addition, sulfide oxides have poor oxidation stability, which severely limits the direct use of high-voltage cathode materials. Oxide solid electrolytes have high air and thermal stability, low manufacturing cost and easy mass production, however, their mechanical rigidity leads to poor interface contact with electrode materials, requiring high-temperature processes or flowing liquid electrolytes to assemble batteries. Halide solid electrolytes have very high ionic conductivity (>10 -3 S·cm -1 ) at room temperature, but still face the problems of easy deliquescence and poor stability.

[0004] In oxyhalide materials, the combination of divalent oxygen ions and halogen ions not only retains the polarity of halogen but also retains the strong bond energy of oxygen, which provides more possibilities for future exploration of new electrolyte materials. According to reports, Li4B7O 12 Cl has a high ionic conductivity at 300℃. However, in previous reports, Li4B7O 12A series of by-products, such as Li2B4O7, are generated in the synthesis process of Cl, thereby reducing the Li4B7O 12 The conductivity and electrochemical performance of Cl.

[0005] Therefore, it is of great significance to develop an oxyhalide material with pure phase and excellent conductivity and electrochemical performance for the field of batteries.

[0006] SUMMARY

[0007] The technical problem solved by the present application is to overcome the defects in the prior art that it is difficult to prepare an oxyhalide with pure phase and excellent conductivity and electrochemical performance, and to provide an oxyhalide and a preparation method thereof and a full solid-state lithium battery. The preparation method of the present application is simple, has high raw material utilization rate and does not contain by-products, and is beneficial to industrial production; the prepared oxyhalide has high ionic conductivity and stability, and has good interface stability with lithium metal; and the prepared full solid-state lithium battery has excellent electrochemical performance.

[0008] In order to prepare an oxyhalide with pure phase, the inventors used a solid phase reaction method for preparation. In the preparation process, by grinding and tabletting the raw materials, the contact between the raw materials can be made more close and the side reactions between the raw materials and the reaction tube can be reduced; by calcining in a vacuum environment, the occurrence of side reactions is further avoided; by using a calcining method combining low-temperature precalcination and high-temperature calcination, the mixture of the components of the raw materials is more uniform and the reaction is more complete, and the generation of by-products is avoided to a greater extent. Through the synergistic cooperation between the technical features, an oxyhalide with pure phase is finally prepared.

[0009] The present application solves the above technical problems by the following technical solutions:

[0010] The present application provides a preparation method of an oxyhalide, the chemical formula of the oxyhalide being Li3B7O 12 ·(LiX)a, X is Cl and / or Br, 0

[0011] (1) After grinding and tabletting a mixture of lithium source and boron source in stoichiometric ratio, the mixture is placed in a reaction tube, the reaction tube is vacuumed and sealed, and then first calcination is performed, the temperature of the first calcination being 300-450 DEG C, and the time of the first calcination being 4-20 h;

[0012] (2) After the first calcination, the intermediate product in the reaction tube is taken out, and then grinding and tabletting are performed again, the mixture is placed in a reaction tube, the reaction tube is vacuumed and sealed, and then second calcination is performed, and then the mixture is cooled to room temperature to obtain the oxyhalide;

[0013] when the lithium source is lithium halide and lithium oxide and the boron source is boron oxide, the temperature of the second calcination is 810-860℃, and the time of the second calcination is 12-30h;

[0014] when the lithium source is lithium halide and lithium borate and the boron source is boron oxide, the temperature of the second calcination is 450-800℃, and the time of the second calcination is 12-30h.

[0015] In the present application, in the oxyhalide, LiX is distributed in Li3B7O 12 the pore structure of the framework.

[0016] In the present application, the lithium halide can be lithium chloride or lithium bromide.

[0017] when the X is Cl, the lithium halide is lithium chloride.

[0018] when the X is Br, the lithium halide is lithium bromide.

[0019] In the present application, in the chemical formula of the oxyhalide, preferably, 0

[0020] In step (2), when the lithium source is lithium chloride and lithium oxide and the boron source is boron oxide, the molar ratio of the lithium chloride, the lithium oxide and the boron oxide can be (0-2):3:7 and excluding 0:3:7, for example, 2:3:7, 1.8:3:7, 1:3:7 or 0.8:3:7, preferably (1.6-1.96):3:7.

[0021] In step (2), when the lithium source is lithium chloride and lithium borate, the boron source is boron oxide and the lithium borate is metaborate, the molar ratio of the lithium chloride, the lithium borate and the boron oxide can be (0-1):3:2 and excluding 0:3:2, for example, 0.4:3:2, 0.5:3:2, 0.9:3:2 or 1:3:2, preferably (0.8-0.98):3:2.

[0022] In the present application, the lithium borate can be metaborate (LiBO2), tetraborate (Li2B4O7) or pentaborate (LiB5O8).

[0023] In step (1) and / or step (2), the operation and conditions of the grinding can be conventional in the art, for example, in a mortar.

[0024] In step (1) and / or step (2), the equipment of the tabletting can be conventional in the art, for example, a tablet press. The pressure of the tabletting is preferably 5-15 MPa, for example, 10 MPa.

[0025] In step (1) and / or step (2), the reaction tube is preferably a quartz tube.

[0026] In step (1) and / or step (2), the vacuum degree of the reaction tube after the vacuuming is preferably less than or equal to 10 -3 Pa.

[0027] In step (1) and / or step (2), the sealing is generally performed by heating and melting the two ends of the reaction tube.

[0028] In the present application, the first calcination and the second calcination are generally performed in a muffle furnace.

[0029] In step (1), the rate of temperature increase to the temperature of the first calcination can be 30-90°C / hour, for example 60°C / hour.

[0030] In step (1), the temperature of the first calcination is preferably 350-450°C, for example 400°C.

[0031] In step (1), the time of the first calcination is preferably 10-15h, for example 12h.

[0032] In step (2), the rate of cooling after the first calcination can be 10°C / hour to 80°C / hour, for example 50°C / hour.

[0033] In step (2), the rate of temperature increase to the temperature of the second calcination can be 30-90°C / hour, for example 60°C / hour.

[0034] In step (2), the rate of cooling after the second calcination can be 10°C / hour to 80°C / hour, for example 50°C / hour.

[0035] In step (2), when the lithium source is lithium chloride and lithium oxide and the boron source is boron oxide, the temperature of the second calcination is for example 830°C, 840°C, 845°C or 850°C, preferably 835-855°C.

[0036] In step (2), when the lithium source is lithium chloride and lithium oxide and the boron source is boron oxide, the time of the second calcination is preferably 15-26h, for example 20h or 24h.

[0037] In step (2), when the lithium source is lithium chloride and lithium borate and the boron source is boron oxide, the temperature of the second calcination is for example 500°C, 600°C or 700°C, preferably 480-610°C.

[0038] In step (2), when the lithium source is lithium chloride and lithium borate and the boron source is boric oxide, the second calcination is preferably performed for 15 to 26 hours, for example, 20 hours or 24 hours.

[0039] The present application also provides an oxyhalide produced by the production method as described above, wherein the ion conductivity of the oxyhalide at 25°C is 0.2 to 2 mS·cm -1 .

[0040] In the present application, the crystal particle size of the oxyhalide is preferably 0.6 to 5 μm, more preferably 0.8 to 1.5 μm, for example, 1 μm.

[0041] In the present application, the ion conductivity of the oxyhalide at 25°C is, for example, 0.25 mS·cm -1 , 0.44 mS·cm -1 , 0.52 mS·cm -1 , 0.72 mS·cm -1 , 0.81 mS·cm -1 , 0.83 mS·cm -1 , 0.92 mS·cm -1 , 1.01 mS·cm -1 , or 1.12 mS·cm -1 , preferably 0.4 to 2 mS·cm -1 .

[0042] In the present application, the electronic conductivity of the oxyhalide at 25°C is preferably 1 x 10 -8 - 1 x 10 -6 S·cm -1 , for example, 3.18 x 10 -7 S·cm -1 , or 6.52 x 10 -7 S·cm -1 , more preferably 2.5 x 10 -7 - 5 x 10 -7 S·cm -1 .

[0043] In the present application, the ion conductivity of the oxyhalide at 30°C is preferably 0.4 to 5 mS·cm -1 , for example, 1.23 mS·cm -1 .

[0044] In the present application, the ion conductivity of the oxyhalide at 40°C is preferably 0.6 to 5 mS·cm -1 , for example, 1.17 mS·cm -1 .

[0045] In the present invention, the ionic conductivity of the oxyhalide at 50°C is preferably 1-5 mS-cm -1 , for example 2.03 mS-cm -1 .

[0046] The present invention also provides a full solid-state lithium battery, comprising a positive electrode, a solid-state electrolyte layer, a buffer layer, and a negative electrode which are sequentially arranged;

[0047] The positive electrode comprises a positive electrode current collector and a positive electrode active material layer on the surface of the positive electrode current collector, the positive electrode active material layer comprising LiFePO4 and the oxyhalide as described above; the solid-state electrolyte layer comprises the oxyhalide as described above, the buffer layer comprises Li6PS5Cl, and the negative electrode comprises a negative electrode current collector and a negative electrode active material layer on the surface of the negative electrode current collector.

[0048] In the present invention, for the positive electrode current collector, a material that does not cause chemical changes and has high conductivity can be used without limitation. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or "aluminum or stainless steel material surface-treated with carbon, nickel, titanium, silver, etc." can be generally used.

[0049] In the present invention, the thickness of the positive electrode current collector can be conventional in the art, for example 16 μm.

[0050] In the present invention, in the positive electrode active material layer, the mass ratio of the LiFePO4 and the oxyhalide can be (2-5): 1, for example 3:1.

[0051] In the present invention, the thickness of the positive electrode active material layer can be 50-500 μm, for example 100 μm.

[0052] In the present invention, the thickness of the solid-state electrolyte layer can be 100-1000 μm, for example 400 μm.

[0053] In the present invention, the thickness of the buffer layer can be 100-1000 μm, for example 420 μm.

[0054] In the present invention, for the negative electrode current collector, a material that does not cause chemical changes and has conductivity can be used without limitation. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, aluminum-cadmium alloy, or "copper, stainless steel material, or aluminum-cadmium alloy surface-treated with carbon, nickel, titanium, or silver" can be used.

[0055] In the present invention, the thickness of the negative electrode current collector can be 4.5-10 μm, for example 6 μm.

[0056] In the present invention, the negative electrode active material layer comprises graphite and / or silicon carbon, for example graphite.

[0057] In the present application, the thickness of the negative active material layer can be 50-500 μm, for example 100 μm.

[0058] In the present application, the all-solid-state lithium battery further comprises a shell, and the positive electrode, the solid-state electrolyte layer, the buffer layer and the negative electrode are packaged in the shell.

[0059] In the present application, the all-solid-state lithium battery refers to a lithium battery without any liquid according to the convention in the art.

[0060] The present application further provides a preparation method of the all-solid-state lithium battery as described above, comprising the following steps:

[0061] The material of the solid-state electrolyte layer is first pressed to obtain the solid-state electrolyte layer;

[0062] The material of the buffer layer is added to one side of the solid-state electrolyte layer and secondly pressed to obtain the buffer layer;

[0063] The material of the positive active material layer is added to the other side of the solid-state electrolyte layer and thirdly pressed to obtain the positive active material layer;

[0064] The material of the negative active material layer is added to one side of the buffer layer and fourthly pressed to obtain the all-solid-state lithium battery.

[0065] In the present application, after the fourth pressing, preferably, the process further comprises placing the positive current collector on one side of the positive active material layer, placing the negative current collector on one side of the negative active material layer and fifthly pressing.

[0066] In the present application, the first pressing, the second pressing, the third pressing, the fourth pressing and the fifth pressing are generally carried out in a solid-state battery mold.

[0067] In the present application, the pressure of the first pressing can be 300-500 MPa, for example 380 MPa.

[0068] In the present application, the pressure of the second pressing can be 200-400 MPa, for example 250 MPa.

[0069] In the present application, the pressure of the third pressing can be 200-400 MPa, for example 250 MPa.

[0070] In the present application, the pressure of the fourth pressing can be 200-400 MPa, for example 250 MPa.

[0071] In the present application, the pressure of the fifth pressing can be 60-180 MPa, for example 100 MPa.

[0072] In the present application, when the all-solid-state lithium battery further comprises a shell, the positive electrode, the solid-state electrolyte layer, the buffer layer and the negative electrode are encapsulated in the shell.

[0073] The raw materials and reagents used in the present application are commercially available.

[0074] On the basis of common general knowledge in the art, the above-mentioned preferred conditions can be combined arbitrarily, thereby obtaining preferred examples of the present application.

[0075] The reagents and raw materials used in the present application are commercially available.

[0076] The positive progress effect of the present application is that:

[0077] (1) The method of the present application has a simple synthesis process, high raw material utilization rate and no by-products, which is beneficial to industrial production;

[0078] (2) The prepared oxyhalide has high ionic conductivity, air stability and thermal stability, and good interface stability with lithium metal;

[0079] (3) The prepared all-solid-state lithium battery has excellent electrochemical performance. BRIEF DESCRIPTION OF DRAWINGS

[0080] Figure 1 is a SEM image of the oxyhalide Li4B7O 12 Cl prepared in Example 1.

[0081] Figure 2 is an XRD pattern of the oxyhalide prepared in Examples 1-2 and Comparative Examples 5-7.

[0082] Figure 3 is an XRD pattern of the oxyhalide prepared in Examples 3-5 and Comparative Example 1. DETAILED DESCRIPTION

[0083] The present application will be further described by way of examples, but the present application is not limited to the scope of the examples. In the following examples, the experimental methods not specified in the specific conditions are selected according to the conventional methods and conditions, or according to the instructions of the goods.

[0084] In the following examples and comparative examples, the manufacturers and purities of the raw materials used are shown in Table 1 below:

[0085] Table 1

[0086] Example 1

[0087] (1) Take 2 mmol of LiCl, 3 mmol of Li2O and 7 mmol of B2O3 according to the stoichiometric ratio, grind them with a mortar, then press them into thin slices with a tablet press at a pressure of 10 MPa, and then place them in a quartz tube. The quartz tube is evacuated and sealed (sealed by heating and melting the two ends of the quartz tube) (vacuum degree <10 Pa), transferred to a muffle furnace for the first calcination, the heating rate is 60 ℃ / h, the first calcination temperature is 400 ℃, and the first calcination time is 12 h; -3 Pa), transferred to a muffle furnace for the first calcination, the heating rate is 60 ℃ / h, the first calcination temperature is 400 ℃, and the first calcination time is 12 h;

[0088] (2) After the first calcination, cool to room temperature at a cooling rate of 50 ℃ / h, take out the intermediate product in the quartz tube, grind and press again (the grinding and pressing conditions are the same as step 1), place them in a quartz tube, evacuate and seal the quartz tube, and then transfer it to a muffle furnace for the second calcination, the heating rate is 60 ℃ / h, the second calcination temperature is 845 ℃, the second calcination time is 22 h, and then cool to room temperature at a cooling rate of 50 ℃ / h, to obtain pure phase oxyhalide Li4B7O 12 Cl.

[0089] Example 2

[0090] Compared with Example 1, except that the second calcination temperature in step (2) is adjusted to 830 ℃, the rest of the operations and conditions are the same as Example 1.

[0091] Example 3

[0092] (1) Take 2 mmol of LiCl, 3 mmol of Li2O and 7 mmol of B2O3 according to the stoichiometric ratio, grind them with a mortar, then press them into thin slices with a tablet press at a pressure of 10 MPa, and then place them in a quartz tube. The quartz tube is evacuated and sealed (sealed by heating and melting the two ends of the quartz tube) (vacuum degree <10 Pa), transferred to a muffle furnace for the first calcination, the heating rate is 60 ℃ / h, the first calcination temperature is 400 ℃, and the first calcination time is 12 h; -3 Pa), transferred to a muffle furnace for the first calcination, the heating rate is 60 ℃ / h, the first calcination temperature is 400 ℃, and the first calcination time is 12 h;

[0093] (2) After the first calcination, cool to room temperature at a cooling rate of 50 ℃ / h, take out the intermediate product in the quartz tube, grind and press again (the grinding and pressing conditions are the same as step 1), place them in a quartz tube, evacuate and seal the quartz tube, and then transfer it to a muffle furnace for the second calcination, the heating rate is 60 ℃ / h, the second calcination temperature is 845 ℃, the second calcination time is 22 h, and then cool to room temperature at a cooling rate of 50 ℃ / h, to obtain pure phase oxyhalide Li4B7O 12 Cl.

[0094] Example 4

[0095] The remaining operations and conditions are the same as those of Example 3, except that the temperature of the second calcination in step (2) is adjusted to 600°C.

[0096] Example 5

[0097] The remaining operations and conditions are the same as those of Example 3, except that the temperature of the second calcination in step (2) is adjusted to 700°C.

[0098] Example 6

[0099] The remaining operations and conditions are the same as those of Example 4, except that the amount of LiCl added in step (1) is adjusted to 0.9 mmol, to obtain oxyhalide Li3B7O 12 ·(LiCl)0 . 9.

[0100] Example 7

[0101] The remaining operations and conditions are the same as those of Example 4, except that LiCl in step (1) is replaced by LiBr, to obtain oxyhalide Li4B7O 12 Br.

[0102] Example 8

[0103] The remaining operations and conditions are the same as those of Example 4, except that the amount of LiCl added in step (1) is adjusted to 0.4 mmol, to obtain oxyhalide Li3B7O 12 ·(LiCl)0 . 4.

[0104] Example 9

[0105] The remaining operations and conditions are the same as those of Example 4, except that 1 mmol of LiCl in step (1) is replaced by 0.25 mmol of LiCl and 0.25 mmol of LiBr, to obtain oxyhalide Li3B7O 12 ·(LiCl) 0.25 (LiBr) 0.25 .

[0106] Example 10

[0107] Preparation of all-solid-state lithium battery

[0108] LiFePO4and the prepared oxyhalide are sand-milled in a sand mill for 20 minutes at a mass ratio of 7.5:2.5 to obtain a material of the positive electrode active material layer; the positive electrode current collector is an aluminum foil with a thickness of 16 μm;

[0109] The prepared oxyhalide is used as a solid-state electrolyte material; Li6PS5Cl is used as a buffer layer material; graphite is used as a material of a negative electrode active material layer; and a copper foil is used as a negative electrode current collector, with a thickness of 6 μm.

[0110] First, 40 mg of the oxyhalide powder is placed in a mold, and a first pressing is performed at a pressure of 380 MPa using a tablet press to obtain a solid-state electrolyte layer; 42 mg of Li6PS5Cl is added to one side of the solid-state electrolyte layer, and a second pressing is performed at a pressure of 250 MPa using the tablet press to obtain a buffer layer; 10 mg of a material of a positive electrode active material layer is added to the other side of the solid-state electrolyte layer, and a third pressing is performed at a pressure of 250 MPa using the tablet press to obtain a positive electrode active material layer; 10 mg of a material of a negative electrode active material layer is added to one side of the buffer layer, and a fourth pressing is performed at a pressure of 250 MPa using the tablet press to obtain a negative electrode active material layer; finally, a positive electrode current collector is placed on one side of the positive electrode active material layer, and a negative electrode current collector is placed on one side of the negative electrode active material layer, and then a fifth pressing is performed at a pressure of 100 MPa using the tablet press to obtain a full-solid-state lithium battery; wherein in the full-solid-state lithium battery, the thickness of the solid-state electrolyte layer is 400 μm, the thickness of the buffer layer is 420 μm, the thickness of the positive electrode active material layer is 100 μm, and the thickness of the negative electrode active material layer is 100 μm.

[0111] Comparative Example 1

[0112] (1) 1 mmol of LiCl, 3 mmol of LiBO2, and 2 mmol of B2O3 are weighed according to the stoichiometric ratio, and then are conventionally ground in a mortar, and are pressed into a thin sheet using a tablet press at a pressure of 10 MPa, and are placed in a quartz tube (without vacuumizing and sealing), and are transferred to a muffle furnace for first calcination, with a heating rate of 60 °C / hour, a first calcination temperature of 400 °C, and a first calcination time of 12 hours.

[0113] (2) After the first calcination, the intermediate product in the quartz tube is taken out, and is ground and pressed again (the grinding and pressing conditions are the same as in step 1), and is placed in a quartz tube, and is transferred to a muffle furnace for second calcination, with a heating rate of 60 °C / hour, a second calcination temperature of 500 °C, and a second calcination time of 24 hours, and then is cooled to room temperature at a cooling rate of 50 °C / hour, to obtain an oxyhalide with impurities.

[0114] Comparative Example 2

[0115] (1) Weigh 2mmol LiCl, 3mmol Li2O and 7mmol B2O3 according to the stoichiometric ratio, grind them in a mortar, place them in a quartz tube, evacuate the tube and seal it (vacuum degree <10 -3 Pa), transferred to a muffle furnace for the first calcination, the heating rate was 60 ° C / hour, the first calcination temperature was 400 ° C, and the first calcination time was 12 h;

[0116] (2) After the first calcination, the product was cooled to room temperature at a cooling rate of 50°C / h. The intermediate product in the quartz tube was taken out, ground again, and placed in a quartz tube. The quartz tube was evacuated and sealed, and then transferred to a muffle furnace for a second calcination at a heating rate of 60°C / h. The temperature of the second calcination was 845°C and the time of the second calcination was 22h. The product was then cooled to room temperature at a cooling rate of 50°C / h to obtain an oxyhalide with an impurity phase.

[0117] Comparative Example 3

[0118] 2mmol LiCl, 3mmol Li2O and 7mmol B2O3 were weighed according to the stoichiometric ratio, ground in a mortar, and then pressed into thin slices using a tablet press at a pressure of 10MPa. The slices were placed in a quartz tube, and the quartz tube was evacuated and sealed (vacuum degree <10 -3 Pa), transferred to a muffle furnace for calcination at a heating rate of 60°C / hour, a calcination temperature of 845°C, and a calcination time of 22h, and then cooled to room temperature at a cooling rate of 50°C / h to obtain an oxyhalide with an impurity phase.

[0119] Comparative Example 4

[0120] Compared with Example 1, except that the temperature of the first calcination in step (1) was adjusted to 200° C., the other operations and conditions were the same as those in Example 1.

[0121] Comparative Example 5

[0122] Compared with Example 1, except that the temperature of the second calcination in step (2) is adjusted to 780°C, the other operations and conditions are the same as those in Example 1.

[0123] Comparative Example 6

[0124] Compared with Example 1, except that the temperature of the second calcination in step (2) is adjusted to 870°C, the other operations and conditions are the same as those in Example 1.

[0125] Comparative Example 7

[0126] Compared with Example 1, except that the temperature of the second calcination in step (2) is adjusted to 890° C., the other operations and conditions are the same as those in Example 1.

[0127] Comparative Example 8

[0128] Comparative Example 9

[0129] Comparative Example 9

[0130] Comparative Example 9

[0131] Effect Example

[0132] (1) Structure and morphology analysis

[0133] Figure 1 is a SEM image of the oxyhalide Li4B7O 12 Cl prepared in Example 1. As can be seen from the figure, the crystal particle size of Li4B7O 12 Cl is about 1 micron.

[0134] (2) XRD characterization

[0135] Figures 2 and 3 are XRD patterns of the oxyhalides prepared in the examples and comparative examples, and Table 2 is the peak position of the XRD of the samples prepared in the examples and comparative examples. According to the test results, no impurity phase was detected in the oxyhalides prepared in Examples 1-9, and there was no significant difference in the XRD patterns, while the oxyhalides prepared in the comparative examples contained Li2B4O7 impurity peaks. As can also be seen from the figures, the oxyhalides prepared in Examples 1-9 showed a crystal structure similar to that of cubic lithium borate (space group F43c), which matched well with PDF #34-0742.

[0136] From the experimental results of the above examples and comparative examples, it can be seen that when the calcination environment is not vacuum, or the raw material is not pressed into tablets, or the first low-temperature calcination is not performed, or the first calcination temperature is not within the range of 350-450°C, or the second calcination temperature is not within the range of 810-860°C or 450-800°C, the oxyhalide prepared will be impure and contain impurities.

[0137] The peak position listed in Table 2 indicates that the peak intensity of the substance at the corresponding position is higher than 100 counts per second; " / " represents that the peak intensity of the substance at the corresponding position is lower than 100 counts per second, i.e. it is considered that no corresponding peak appears at the position, wherein "counts per second" represents the number of x-ray particles accepted by the detector per second.

[0138] Table 2

[0139] (3) Ion conductivity test

[0140] At room temperature 25℃, 300 mg of the oxyhalide powder prepared in Example 1-9 and Comparative Example 1-9 was first pressed into a thin sheet at 380 Mpa, and then placed in a sealed vacuum quartz tube and calcined at 600℃ for 20 h. After calcination, the particles were transferred to a PEEK sleeve mold, and electrochemical impedance testing was performed using an electrochemical workstation (CHI, 650E) with an applied voltage of 0.05 V and a frequency range of 10 -1 Hz to 10 6 Hz. The test results are shown in Table 3.

[0141] The formula for calculating the lithium ion conductivity of the oxyhalide solid-state electrolyte is: ion conductivity p = L / RS, L is 3 mm, S represents the area of a circle with a radius of 5 mm, and R is the impedance.

[0142] Table 3

[0143] The lithium ion conductivity of the oxyhalide solid-state electrolyte prepared in Example 1 at different temperatures is shown in Table 4.

[0144] Table 4

[0145] (4) Electronic conductivity test

[0146] At room temperature 25℃, the oxyhalide solid-state electrolyte powder prepared in Example 1-2 and Comparative Example 6-7 was placed in a PEEK sleeve, two ion blocking electrodes were placed at both ends of the powder, and then a pressure of 380 Mpa was applied. Direct current (DC) polarization measurement was performed using an electrochemical workstation (CHI, 650E) to test the electronic conductivity at different polarization voltages. The formula for calculating the electronic conductivity is: σ e = LI / SE, σ e is the electronic conductivity, L is the thickness of the Li4B7O 12 Cl electrolyte (0.3 cm), S is the area of the Li4B7O 12 Cl electrolyte (0.785 cm 2 ), E is the polarization voltage (1 V), and I is the steady-state current.

[0147] The test results are shown in Table 5.

[0148] Table 5

[0149] (5) Stability of Li4B7O 12 Cl

[0150] The oxyhalide Li4B7O 12 Cl was exposed to air for six months (room temperature) and sintered in air at 300°C in a muffle furnace for 12 hours, respectively, and characterized by XRD. According to the test results, after exposure to air for six months or sintering in air, all the peaks were consistent with those of the initial sample, indicating that Li4B7O 12 Cl has very high air stability and thermal stability.

[0151] (6) Li4B7O 12 Cl and lithium metal

[0152] The oxyhalide Li4B7O 12 Cl prepared in Example 1 was studied.

[0153] The number of ion transference has a negative impact on the concentration polarization during the charging and discharging process, thereby improving the power density of the battery and limiting the movement of anions in the lithium salt.

[0154] By assembling Li|Li4B7O 12 Cl|Li symmetric half-cells, the lithium ion transference number of Li4B7O 12 Cl was studied. The assembly process of the half-cell is as follows:

[0155] The lithium metal sheet was rolled into a thin sheet and cut into a round sheet with a 1 mm diameter circular cutter; 40 mg of Li4B7O 12 Cl powder was placed in the mold, and after pressing with a tablet press at a pressure of 380 MPa, one of the round sheets cut in advance was placed on each side of Li4B7O 12 Cl, and then pressed at a pressure of 100 MPa to obtain Li|Li4B7O 12 Cl|Li symmetric half-cells.

[0156] Li|Li4B7O 12 Cl|Li batteries were used to measure the Li 12 + transference number (T Li+ ) of Li4B7O + Cl electrolyte. The constant potential measurement was carried out at a direct current polarization voltage of 0.05 V to obtain the initial current and the steady current. The initial resistance (R0) before the constant potential test and the resistance (R s ) after the measurement were obtained by alternating current impedance measurement at a frequency of 10 -1 Hz to 10 6 Hz. The transference number of the electrolyte was obtained from the following formula:

[0157] where ΔV(0.01V) is the direct current polarization voltage applied to the sample, I0is the initial current, I s is the stable current.

[0158] According to the experimental results, it is calculated that the lithium ion transference number of Li4B7O 12 Cl is 0.74. The higher the lithium ion transference number is, the lower the transference number of the corresponding anion is, and the smaller the concentration polarization is, which will hinder the growth of lithium dendrites and the occurrence of some side reactions.

[0159] In order to evaluate the electrochemical properties of Li4B7O 12 Cl solid electrolyte, the assembled Li|Li4B7O 12 Cl|Li symmetrical half-batteries were tested at 50℃, 0.01mA·cm -2 and 0.05mA·cm -2 respectively by galvanostatic charge-discharge cycling. The symmetrical half-batteries reached the polarization voltage of 5V after 40 cycles (80 hours) and 200 cycles (400 hours) at the current density of 0.05mA·cm -2 and 0.01mA·cm -2 respectively.

[0160] (7) Electrochemical performance of all-solid-state lithium battery (ASSLB)

[0161] Based on Li4B7O 12 Cl prepared in Example 1, ASSLB was assembled according to the above method for research. The battery test system (LAND, CT3002A) tested the galvanostatic charge-discharge characteristics of LiFePO4@Li4B7O 12 Cl|Li4B7O 12 Cl|Li6PS5Cl|graphite ASSLB at 50℃.

[0162] According to the test results, the initial discharge capacity and the 100th discharge capacity of the assembled all-solid-state lithium battery are 75mAh·g -1 and 88mAh·g -1 respectively. The initial coulombic efficiency of ASSLB is 78%. ASSLB has high cycle stability and reversible capacity. After 180 cycles, the specific discharge capacity is 83.6mAh·g -1 , and the coulombic efficiency is 76%.

[0163] Although the specific embodiments of the present application are described above, it should be understood by those skilled in the art that the present application is only illustrative, and the scope of protection of the present application is defined by the appended claims. Those skilled in the art can make various changes or modifications to the embodiments without departing from the principles and the essence of the present application, and such changes and modifications fall within the scope of protection of the present application.

Claims

1. A method for preparing an oxyhalide, characterized in that: The chemical formula of the oxyhalide is Li3B7O 12 (LiX)a, where X is Cl and / or Br, and 0<a≤1, comprises the following steps: (1) grinding and tableting a mixture of a lithium source and a boron source weighed in a stoichiometric ratio, placing the mixture in a reaction tube, evacuating and sealing the reaction tube, and then performing a first calcination at a temperature of 300-450° C. for a time of 4-20 h; (2) After the first calcination, the mixture is cooled to room temperature, the intermediate product in the reaction tube is taken out, ground again, pressed into tablets, and placed in a reaction tube. The reaction tube is evacuated and sealed, and the mixture is calcined for the second time, and then cooled to room temperature to obtain the oxyhalide; When the lithium source is lithium halide and lithium oxide and the boron source is boron oxide, the temperature of the second calcination is 810-860° C., and the time of the second calcination is 12-30 hours; When the lithium source is lithium halide and lithium borate and the boron source is boron oxide, the temperature of the second calcination is 450-800° C. and the time of the second calcination is 12-30 hours.

2. The method for preparing an oxyhalide according to claim 1, wherein: The preparation method satisfies one or more of the following conditions: (1) In step (1) and / or step (2), the tableting pressure is 5-15 MPa; (2) In step (1) and / or step (2), the reaction tube is a quartz tube; (3) In step (1) and / or step (2), after the vacuuming, the vacuum degree of the reaction tube is less than or equal to 10 -3 Pa; (4) The lithium borate is lithium metaborate, lithium tetraborate or lithium pentaborate; (5) The lithium halide is lithium chloride or lithium bromide; (6) In the chemical formula of the oxyhalide, 0.8<a<0.

98.

3. The method for preparing an oxyhalide according to claim 1 or 2, wherein: In step (1), the temperature of the first calcination is 350-450°C; And / or, in step (1), the first calcination time is 10-15 hours.

4. The method for preparing an oxyhalide according to claim 1 or 2, wherein: In step (2), when the lithium source is lithium chloride and lithium oxide and the boron source is boron oxide, the temperature of the second calcination is 835-855° C.; And / or, in step (2), when the lithium source is lithium chloride and lithium oxide and the boron source is boron oxide, the second calcination time is 15-26 hours; And / or, in step (2), when the lithium source is lithium chloride and lithium oxide and the boron source is boron oxide, the molar ratio of the lithium chloride, the lithium oxide and the boron oxide is (1.6-1.96):3:

7.

5. The method for preparing an oxyhalide according to claim 1 or 2, wherein: In step (2), when the lithium source is lithium chloride and lithium borate and the boron source is boron oxide, the temperature of the second calcination is 480-610° C.; And / or, in step (2), when the lithium source is lithium chloride and lithium borate and the boron source is boron oxide, the second calcination time is 15-26 hours; And / or, in step (2), when the lithium source is lithium chloride and lithium borate, the boron source is boron oxide and the lithium borate is lithium metaborate, the molar ratio of the lithium chloride, the lithium borate and the boron oxide is (0.8-0.98):3:

2.

6. An oxyhalide, characterized in that It is prepared according to the preparation method of the oxyhalide according to any one of claims 1 to 5, and the ionic conductivity of the oxyhalide at 25° C. is 0.2-2 mS·cm -1 .

7. An all-solid-state lithium battery, characterized in that: It includes a positive electrode, a solid electrolyte layer, a buffer layer and a negative electrode arranged in sequence; The positive electrode comprises a positive electrode current collector and a positive electrode active material layer located on the surface of the positive electrode current collector, the positive electrode active material layer comprises LiFePO4 and the oxyhalide according to claim 6; the solid electrolyte layer comprises the oxyhalide according to claim 6, the buffer layer comprises Li6PS5Cl, and the negative electrode comprises a negative electrode current collector and a negative electrode active material layer located on the surface of the negative electrode current collector.

8. The all-solid-state lithium battery according to claim 7, wherein: The all-solid-state lithium battery meets one or more of the following conditions: (1) In the positive electrode active material layer, the mass ratio of the LiFePO4 to the oxyhalide is (2-5):1; (2) The thickness of the positive electrode active material layer is 50-500 μm; (3) The thickness of the solid electrolyte layer is 100-1000 μm; (4) The thickness of the buffer layer is 100-1000 μm; (5) The thickness of the negative electrode active material layer is 50-500 μm.

9. A method for preparing an all-solid-state lithium battery according to claim 7 or 8, characterized in that: It includes the following steps: Performing a first pressing on the material of the solid electrolyte layer of the all-solid-state lithium battery to obtain the solid electrolyte layer; Adding the material of the buffer layer of the all-solid-state lithium battery to one side of the solid electrolyte layer and performing a second pressing to obtain the buffer layer; adding the material of the positive electrode active material layer of the all-solid-state lithium battery to the other side of the solid electrolyte layer and performing a third pressing to obtain the positive electrode active material layer; The material of the negative active material layer of the all-solid-state lithium battery is added to one side of the buffer layer and subjected to a fourth pressing process to obtain the all-solid-state lithium battery.

10. The method for preparing an all-solid-state lithium battery according to claim 9, wherein: The preparation method satisfies one or more of the following conditions: (1) After the fourth pressing, the process further includes: placing the positive electrode current collector on one side of the positive electrode active material layer, placing the negative electrode current collector on one side of the negative electrode active material layer, and performing a fifth pressing process; (2) the first pressing pressure is 300-500 MPa; (3) The second pressing pressure is 200-400 MPa; (4) The pressure of the third pressing is 200-400 MPa; (5) The fourth pressing pressure is 200-400 MPa; (6) The pressure of the fifth pressing is 60-180 MPa.

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