A solid electrolyte, a separator for a secondary battery, and a secondary battery

Abstract

The present invention relates to the field of electrochemistry technology, and particularly relates to a solid electrolyte, a separator for a secondary battery, and a secondary battery. The solid electrolyte described in the present invention includes an inorganic material, and the chemical formula of the inorganic material is: Li4W 1‑x Mo x O5, where 0 < x ≤ 0.5. In the present invention, Mo is used to dope the existing Li4WO5 material, and the addition amount of Mo is strictly controlled by doping Mo into the Li4WO5 material to optimize the material composition and lattice structure of the solid electrolyte, and an inorganic material with the chemical formula Li4W 1‑x Mo x O5 is obtained. The molybdenum-doped lithium tungstate solid electrolyte has characteristics such as high conductivity, wide electrochemical window, low interfacial impedance, economic and environmental friendliness, etc., and can effectively improve the safety stability, service life of the solid battery and is environmentally friendly. At the same time, it can effectively improve the mechanical properties and anti-shrinkage properties of the composite film, improve the ability of the composite film to inhibit lithium dendrites, and also has a certain promoting effect on the high-rate discharge ability of power batteries.

Description

Technical Field

[0001] The present invention relates to the field of electrochemical technology, and in particular to a solid electrolyte, a separator for a secondary battery, and a secondary battery. Background Art

[0002] Lithium-ion batteries have the characteristics of high operating voltage, high energy density, long cycle life, low self-discharge, no memory effect, and environmental friendliness, and have become an ideal power source for mobile communications, power tools, medical devices, etc. With the vigorous promotion of new energy vehicles at home and abroad, lithium-ion batteries have become the first choice for electric vehicle power sources due to their unique advantages, thus giving lithium-ion batteries a broader development prospect.

[0003] At present, the polymer electrolytes in lithium-ion batteries put into industrial production have problems such as poor low-temperature performance and poor high-power output capacity. For example, linear or cross-linked polymers obtained by the polymerization reaction of ethylene oxide and propylene oxide are mainly used as ion-conductive polymers of solid polymer electrolytes. In lithium batteries using polymers synthesized from these monomers as a matrix, the cross-linked network structure of the polymer matrix and the strong interaction between lithium ions and the alkylene oxides remaining in the matrix reduce the mobility of lithium ions, resulting in insufficient conductivity of the solid electrolyte and a reduced cycle life of the battery.

[0004] At the same time, the separator of the lithium-ion battery acts as a separating medium between the positive and negative electrodes, preventing the positive and negative electrodes from contacting and short-circuiting, which has a great impact on the safety of the battery. The separators in the prior art are mainly porous membranes composed of polyolefins such as polyethylene and polypropylene; however, the porous membranes of polyolefins have inherent deficiencies: the melting point of polyethylene is about 130°C, and the melting point of polypropylene is about 160°C. The porous membranes of these two materials will shrink to a large extent above 90°C. When the lithium-ion battery has an internal short circuit or an external short circuit, the separator is easy to shrink, causing the positive and negative electrodes to contact and produce a larger short circuit, which can easily lead to thermal runaway of the battery, fire and explosion. In recent years, with the high demand and high requirements of new energy vehicles for power lithium batteries, higher requirements have been put forward for the various performance of separators.

[0005] Li4WO5 itself is a widely used multi-purpose material, but its low ionic conductivity limits its application in lithium batteries. Summary of the invention

[0006] In order to solve the technical problems of insufficient conductivity and easy thermal runaway of existing lithium-ion batteries, the present invention provides a solid electrolyte, a secondary battery separator and a secondary battery by mixing an inorganic material Li4W 1-x Mo x O5(0 <x≤0.05)作为本体材料制备固态电解质,或者将无机材料Li4W1-x Mo x O5(0 < x ≤ 0.05) is coated on the surface of the porous layer of the separator or incorporated into the interior of the porous layer to optimize and improve the conductivity, thermal shrinkage, and thermal stability of the secondary battery to the greatest extent.

[0007] To achieve the above object, a first aspect of the present invention provides a solid electrolyte, which includes an inorganic material, and the chemical formula of the inorganic material is: Li4W 1-x Mo x O5, where 0 < x ≤ 0.5.

[0008] The inventor of the present invention found that the Mo-modified lithium tungstate solid electrolyte has characteristics such as high conductivity, wide electrochemical window, low interfacial impedance, economy, and environmental friendliness. Therefore, it can effectively improve the safety stability, life, and electrochemical performance of the solid battery and is environmentally friendly. At the same time, it can effectively improve the mechanical properties and shrinkage resistance of the composite film, improve the ability of the composite film to inhibit lithium dendrites, and also has a certain promoting effect on the high-rate discharge ability of power batteries.

[0009] The present invention prepares a solid electrolyte by using an inorganic material with the chemical formula: Li4W 1-x Mo x O5(0 < x ≤ 0.5) as the main material to improve the ionic conductivity of the solid electrolyte and maximize the optimization and improvement of the cyclic use performance of the secondary battery; at the same time, the inventor of the present invention also uses Li4W 1-x Mo x O5(0 < x ≤ 0.5) inorganic material as a separator coating, and coats the inorganic material on the surface of the separator to improve the performance of the separator, for example, thermal stability, high temperature resistance, and puncture strength.

[0010] Furthermore, the inorganic material has a crystal structure, the crystal structure is a triclinic structure, and has a P-1 space group, and its unit cell parameters are: α = 101 - 102°, β = 100 - 102°, γ = 107 - 109°,

[0011] Furthermore, the solid electrolyte is an inorganic ceramic sheet or an inorganic-organic composite solid electrolyte film.

[0012] Furthermore, the solid electrolyte is an inorganic ceramic sheet, the thickness of the inorganic ceramic sheet is 0.1 mm to 2 mm, and the particle size of the sintered particles in the inorganic ceramic sheet is 200 nm to 50 μm. Preferably, the thickness of the inorganic ceramic sheet is 0.1 mm to 1 mm, and the particle size of the sintered particles in the inorganic ceramic sheet is 200 nm to 40 μm.

[0013] Further, the solid electrolyte is an inorganic-organic composite solid electrolyte film, and the inorganic-organic composite solid electrolyte film further includes a polymer matrix and a lithium salt. The mass percentage of the inorganic material in the inorganic-organic composite solid electrolyte film is 2% to 36%; preferably 5 - 30%.

[0014] Further, the polymer matrix is selected from one or more of poly(ethylene oxide)-based polymers, poly(vinyl acetate)-based polymers, poly(ethylene imine)-based polymers, poly(vinylidene fluoride)-based polymers, polyacrylonitrile-based polymers, and poly(methyl methacrylate)-based polymers. The mass percentage of the polymer matrix in the inorganic-organic composite solid electrolyte film is 38% to 69%; preferably 40 - 65%;

[0015] The lithium salt is selected from those with Li + as the cation and F - 、Cl - 、Br - 、I - 、NO3 - 、N(CN)2 - 、BF4 - 、ClO4 - 、AlO4 - 、AlCl4 - 、PF6 - 、SbF6 - 、AsF6 - 、BF2C2O4 - 、BC4O8 - 、(CF3)2PF4 - 、(CF3)3PF3 - 、(CF3)4PF2 - 、(CF3)5PF - 、(CF3)6P - 、CF3SO3 - 、C4F9SO3 - 、CF3CF2SO3 - 、(CF3SO2)2N - 、(F2SO2)2N - 、CF3CF2(CF3)2CO - 、(CF3SO2)2CH - 、CF3(CF2)7SO3 - 、CF3CO2 - 、CH3CO2 - 、SCN - 、(CF3CF2SO2)2N -One or more of any of the following as anions, and the mass percentage of the lithium salt in the inorganic-organic composite solid electrolyte film is 18% to 43%; preferably 20% - 40%.

[0016] Furthermore, the thickness of the inorganic-organic composite solid electrolyte film is 5μm to 200μm, and the particle size of the inorganic material in the inorganic-organic composite solid electrolyte film is 20nm to 50μm. Preferably, the thickness of the inorganic-organic composite solid electrolyte film is 10μm to 100μm, and the particle size of the inorganic material in the inorganic-organic composite solid electrolyte film is 30nm to 40μm.

[0017] In a second aspect of the present invention, there is provided a separator for a secondary battery, the separator comprising a porous substrate and a porous layer laminated on at least one side of the porous substrate, the porous layer containing an inorganic material, the inorganic material being coated on the surface of the porous layer or blended inside the porous layer, and the chemical formula of the inorganic material being:

[0018] Li4W 1-x Mo x O5, where 0 < x ≤ 0.5.

[0019] Furthermore, the mass percentage of the inorganic material in the porous layer is 60% to 95%; preferably 80% - 90%.

[0020] Preferably, the particle size of the inorganic material contained in the porous layer is 20nm to 50μm; more preferably 20nm to 500nm.

[0021] Preferably, the porous substrate is a thermoplastic resin with a melting point below 200°C; furthermore, the porous substrate is a polyolefin-based porous substrate.

[0022] Preferably, the polyolefin-based porous substrate includes polyethylene, polypropylene, polyethylene polymers, polypropylene polymers, and mixtures thereof.

[0023] Preferably, the thickness of the separator for a secondary battery is 3 to 100μm; more preferably, 5 to 90μm; further preferably, 10 to 50μm.

[0024] Furthermore, the porous layer can be coated only on one side of the porous substrate or on both sides of the porous substrate. In addition, the porous layer can be provided to cover the entire porous substrate, or can also be provided to cover only a part of the porous substrate.

[0025] The porous layer further includes a binder. In the single-layer composite separator, based on the total mass of the porous layer being 100%, the mass percentage of the inorganic material is 60-95%, and the mass percentage of the binder is 5-40%; in the double-layer composite separator, based on the total mass of the porous layer being 100%, the mass percentage of the inorganic material is 60-95%, and the mass percentage of the binder is 5-40%.

[0026] Further, the inorganic material has a crystal structure, the crystal structure is a triclinic structure, and has a P-1 space group, and its unit cell parameters are: α = 101-102°, β = 100-102°, γ = 107-109°,

[0027] In the present invention, by coating an inorganic material with the chemical formula Li4W 1-x Mo x O5(0 < x ≤ 0.05) on the surface of the porous layer or blending it inside the porous layer, the conductivity of the separator of the secondary battery can be effectively improved and the thermal shrinkage of the separator of the secondary battery can be improved.

[0028] The third aspect of the present invention provides a secondary battery, which includes the aforementioned solid electrolyte or the aforementioned separator for the secondary battery, and the secondary battery is any one of a semi-solid battery, a quasi-solid battery, a all-solid battery, a lithium-ion battery or a lithium battery.

[0029] The fourth aspect of the present invention provides an application of an inorganic material in improving the conductivity, thermal shrinkage and thermal stability of a solid electrolyte, a separator for a secondary battery and a secondary battery, and the chemical formula of the inorganic material is: Li4W 1-x Mo x O5, where 0 < x ≤ 0.5.

[0030] Compared with the prior art, the present invention has the following advantages:

[0031] (1) The solid electrolyte described in the present invention includes an inorganic material, and the chemical formula of the inorganic material is: Li4W 1- x Mo x O5, where 0 < x ≤ 0.05. The lithium tungstate solid electrolyte modified by Mo has characteristics such as high conductivity, wide electrochemical window, low interfacial impedance, economic and environmental protection, etc., and can effectively improve the safety stability, life and electrochemical performance of the solid battery, and is environmentally friendly; at the same time, it can effectively improve the mechanical properties and anti-shrinkage properties of the composite film, improve the ability of the composite film to inhibit lithium dendrites, and also has a certain promoting effect on the high-rate discharge ability of the power battery;

[0032] (2) The inorganic material is used as a coating for the separator of a secondary battery, and is coated on the surface of the porous layer or incorporated into the interior of the porous layer, and then the porous layer containing the inorganic material is laminated on at least one surface of the porous substrate, which can effectively improve the conductivity and thermal shrinkage of the separator of the secondary battery;

[0033] (3) The secondary battery prepared by using the solid electrolyte and / or separator of the present invention has a high initial discharge capacity, is not prone to short circuit, has strong practicability, remarkable use effect, and has a good market prospect. Description of the Drawings

[0034] Figure 1 It is the XRD phase characterization spectrum of the inorganic material prepared in the example of the present invention;

[0035] Figure 2 It is the SEM image of the inorganic ceramic sheet prepared in Example 1 of the present invention;

[0036] Figure 3 It is the conductivity data graph of the solid electrolyte prepared in the example of the present invention at room temperature;

[0037] Figure 4 It is the thermal shrinkage resistance graph of the composite separator prepared in the example of the present invention at different temperatures;

[0038] Figure 5 It is the scanning electron micrograph of the polypropylene porous membrane in the present invention;

[0039] Figure 6 It is the scanning electron micrograph of the composite separator with the inorganic material as the coating in the present invention. Detailed Embodiments

[0040] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the protection scope of the present invention.

[0041] The present invention will be described in detail below through examples.

[0042] Example 1

[0043] I. Preparation of Secondary Battery

[0044] (1) Preparation of Solid Electrolyte

[0045] Step 1: Mix LiOH·H2O powder, WO3 powder, and MoO3 powder in a mass ratio of LiOH·H2O:WO3:MoO3 = 3.425 g:4.181 g:0.288 g. Ball mill them in a planetary ball mill at a rotation speed of 250 rpm for 3 h. Then, put the ball-milled powder into an alumina crucible and place it in a muffle furnace for calcination at 850 °C for 3 h. After cooling, the inorganic material Li4W 0.9 Mo 0.1 O5 with an average particle size of 1 μm can be obtained;

[0046] Step 2:

[0047] Perform secondary ball milling on the above inorganic material with an average particle size of 1 μm to refine it to D V 50 of approximately 100 - 200 nm, and then perform rapid sintering by the SPS (Spark Plasma Sintering) method. After annealing at a certain temperature, polish it with sandpaper to obtain an inorganic ceramic sheet as a solid electrolyte. The thickness of the inorganic ceramic sheet is approximately 0.1 - 2 mm.

[0048] (2) Preparation of the positive electrode sheet

[0049] Mix the positive electrode active material LiFePO4, conductive carbon black Super-P, and binder polyvinylidene fluoride (PVDF) in a mass ratio of 93:4:3. Then disperse them in N-methyl-2-pyrrolidone (NMP) to obtain a positive electrode slurry. Coat the slurry evenly on both sides of the aluminum foil, dry, calender, and vacuum dry it. After welding an aluminum lead wire with an ultrasonic welder, the positive electrode sheet is obtained. The thickness of the positive electrode sheet is 120 - 150 μm.

[0050] (3) Assembly of the battery

[0051] Assemble the positive electrode sheet, solid electrolyte, and negative lithium metal prepared in this example into a solid-state battery.

[0052] II. Battery performance testing

[0053] (1) XRD phase characterization

[0054] Put the inorganic material into an X-ray diffractometer for scanning. X-ray (Cu): voltage 40 kV, current 20 mA; the scanning 2θ angle range is 10 - 80°, the scanning method is continuous scanning, the scanning speed is 0.1 s / step, and the step size is 0.02° / step. The obtained characterization spectrum is shown in Figure 1 .

[0055] (2) Ion conductivity test

[0056] A gold film is sputtered on both sides of the solid electrolyte as a conductive electrode (blocking electrode), and then the room-temperature AC impedance of the sample is measured on an electrochemical workstation. The AC impedance test is carried out from a high frequency of 10 6 Hz to a low frequency of 0.1 Hz, and then the total impedance value R of the electrolyte is obtained (including the bulk resistance and the grain boundary resistance, see Figure 3 ), and the ionic conductivity of the inorganic ceramic sheet as the solid electrolyte is measured at room temperature. The calculation formula is as follows:

[0057] σ = L / A·R,

[0058] where L is the thickness of the solid electrolyte, A is the area of the gold film, and R is the total resistance value of the solid electrolyte.

[0059] (3) Initial discharge capacity

[0060] The formed battery is charged at a constant current of 0.1 C to 3.8 V at 25 ± 1 °C, and then switched to constant voltage charging with a cut-off current of 0.05 C; then, the battery is discharged at a constant current of 0.1 C to 2.8 V, and the capacity of the battery discharged at a constant current of 0.1 C at room temperature to 2.8 V is obtained. The ratio of this discharge capacity to the mass of the positive active material is the initial discharge specific capacity.

[0061] Examples 2-9

[0062] Examples 2-9 are used to illustrate the secondary battery disclosed in the present invention, including most of the operation steps in Example 1, and the differences are as follows:

[0063] During the preparation process of the solid electrolyte, LiOH·H2O powder, WO3 powder, and MoO3 powder with different mass ratios are added to prepare inorganic materials with the chemical formulas shown in Examples 2-9 in Table 1, and the inorganic ceramic sheets corresponding to Examples 2-9 are respectively prepared from the obtained inorganic materials. The test results of the ionic conductivity of the inorganic ceramic sheets and the results of the initial discharge capacity of the secondary batteries made from the inorganic ceramic sheets are shown in Table 1.

[0064] Comparative Examples 1-2

[0065] Comparative Examples 1-2 are used to illustrate the secondary battery disclosed in the present invention, including most of the operation steps in Example 1, and the differences are as follows:

[0066] During the preparation process of the solid electrolyte, LiOH·H2O powder, WO3 powder, and MoO3 powder with different mass ratios are added to prepare inorganic materials with the chemical formulas shown in Comparative Examples 1-2 in Table 1, and the inorganic ceramic sheets corresponding to the inorganic materials are respectively prepared. The test results of the ionic conductivity of the obtained inorganic ceramic sheets and the results of the initial discharge capacity of the secondary batteries made from the inorganic ceramic sheets are shown in Table 1.

[0067] Table 1

[0068]

[0069] Combined with Table 1, Figure 1-3 and the data of Examples 1-9 and Comparative Examples 1-2, it can be seen that, first of all, within the range of 0 < x ≤ 0.05, the inorganic materials with the chemical formula Li4W 1-x Mo x O5 are all relatively pure phases, and there are a small number of visible impurity peaks (x ≥ 0.3) in the XRD phase characterization spectrum of Figure 1 ; secondly, as shown in

[0070] , before the impedance test, by testing the SEM image of the inorganic ceramic sheet prepared from the inorganic material, its density is greater than 90%. It can be seen that doping Mo into Li4WO5 can increase the density of the inorganic material, which is beneficial to reducing the grain boundary impedance; Figure 2 At the same time, combined with

[0071] and the data in Table 1, it can be clearly seen that when 0 < x ≤ 0.05, the total conductivity of the solid electrolyte prepared from the inorganic material of Li4W Figure 3 doped with Mo and having the chemical formula Li4W 1-x Mo x O5 can be increased by nearly 40 times compared with the total conductivity of the solid electrolyte prepared from Li4WO5 material. Specifically, when x = 0.0, that is, the total conductivity of the solid electrolyte prepared from Li4WO5 material without Mo doping is only 1.2×10 -6 S / cm, while the total conductivity of the solid electrolyte obtained from Li4WO5 doped with Mo and having the chemical formula Li4W 1- x Mo x O5 (0 < x ≤ 0.05) is not less than 3.0×10 -6 S / cm, and when x = 0.1, the total conductivity of the solid electrolyte prepared from the inorganic material can be as high as 5.6×10 -5 S / cm.

[0072] Examples 10-12

[0073] Examples 10-12 are used to illustrate the secondary battery disclosed in the present invention, including most of the operation steps in Example 1, and the differences are as follows:

[0074] In the preparation process of the inorganic-organic composite solid electrolyte membrane, the chemical formulas obtained in Example 1, Example 7, and Example 9 are successively Li4W 0.9 Mo 0.1O5, Li4W 0.7 Mo 0.3 O5, Li4W 0.5 Mo 0.5 The inorganic materials of O5 were respectively mixed with the polymer matrix and the lithium salt in the contents shown in Examples 10 - 12 in Table 2 for preparation;

[0075] The specific process is to weigh the polymer matrix, Li4WO5 - Mo - based powder (Li4W 0.9 Mo 0.1 O5 or Li4W 0.7 Mo 0.3 O5 or Li4W 0.5 Mo 0.5 O5) and the lithium salt in a certain proportion in a glove box and mix them in an acetonitrile solution. After stirring for 24 h, a viscous slurry with uniformly dispersed Li4WO5 - Mo - based particles can be obtained. The slurry is coated on a polytetrafluoroethylene plate. After the acetonitrile solvent completely volatilizes, a flexible and self - supporting inorganic - organic composite solid electrolyte film can be obtained. The ion conductivity test results of the obtained inorganic - organic composite solid electrolyte film and the first discharge capacity results of the secondary battery made by using the inorganic - organic composite solid electrolyte film are shown in Table 2.

[0076] Comparative Example 3

[0077] Comparative Example 3 is used to illustrate the secondary battery disclosed in the present invention, including most of the operation steps in Example 1. The difference is that:

[0078] During the preparation process of the solid electrolyte, the inorganic material with the chemical formula Li4WO5 obtained in Comparative Example 1, the polymer matrix and the lithium salt in the contents shown in Comparative Example 3 in Table 2 are dissolved and mixed in an acetonitrile solution. After stirring for 24 h, a viscous slurry with uniformly dispersed Li4WO5 - based particles can be obtained. The slurry is coated on a polytetrafluoroethylene plate. After the acetonitrile solvent completely volatilizes, an inorganic - organic composite solid electrolyte film is obtained. The ion conductivity test results of the obtained inorganic - organic composite solid electrolyte film and the first discharge capacity results of the secondary battery made by using the inorganic - organic composite solid electrolyte film are shown in Table 2.

[0079] Table 2

[0080]

[0081] Combined with the data in Table 2, it can be seen that by doping Mo into Li4WO5 to obtain Li4W with 1-x Mo xInorganic materials with the chemical formula of O5(0 < x ≤ 0.05) can significantly improve the conductivity of the inorganic-organic composite solid electrolyte film when preparing the inorganic-organic composite solid electrolyte film. Specifically, when directly preparing the inorganic-organic composite solid electrolyte film with the Li4WO5 material without Mo doping, its conductivity is only 2*10 -6 S / cm, while for the inorganic material with the chemical formula of Li4W 1-x Mo x O5(0 < x ≤ 0.05) obtained by doping Li4WO5 with Mo, the conductivity of the inorganic-organic composite solid electrolyte film prepared by the same preparation method can reach up to 7*10 -5 S / cm.

[0082] Example 13

[0083] I. Preparation of primary and secondary batteries

[0084] (1) Preparation of composite separator

[0085] Step 1: Preparation of inorganic mixed slurry: Weigh 200 mg of binder PVDF and 800 mg of Li4W 0.9 Mo 0.1 O5 inorganic material in a ratio of 1:4, and then drop 3800 mg of NMP solvent, and stir for 24 h to obtain the inorganic coating layer slurry;

[0086] Step 2: Coating of inorganic mixed slurry: Cut a polypropylene porous membrane with a length of 20 cm and a thickness of 25 μm and lay it flat on the coater, then pour the uniformly stirred inorganic mixed slurry evenly on one side, and control the 50-μm specification scraper to uniformly coat the slurry on the polypropylene porous membrane at a linear speed of 3 m / min. After coating, put it into a vacuum drying oven and vacuum dry at 60 °C for 12 h to obtain a lithium-ion battery composite separator with Li4W 0.9 Mo 0.1 O5 as the coating.

[0087] (2) Preparation of electrolyte

[0088] Dissolve LiPF6 at a concentration of 1 mol / L in a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (EC:EMC = 1:1 volume ratio), and add 1% of fluoroethylene carbonate (FEC).

[0089] (3) Preparation of positive electrode sheet

[0090] Mix the positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1O2, conductive carbon black Super-P, and binder polyvinylidene fluoride (PVDF), and then disperse them in N-methyl-2-pyrrolidone (NMP) to obtain the positive electrode slurry. Coating the slurry evenly on both sides of the aluminum foil, drying, rolling, and vacuum drying, and then welding the aluminum lead-out wire with an ultrasonic welder to obtain the positive electrode sheet, and the thickness of the positive electrode sheet is 120-150 μm.

[0091] (4) Preparation of the negative electrode sheet

[0092] Cut and punch the lithium sheet into pieces in the glove box, and the thickness of the negative electrode sheet is 100-120 μm.

[0093] Arrange the positive electrode sheet and the negative electrode sheet facing each other, and insert the separator with the coated surface facing the positive electrode sheet between the positive electrode sheet and the negative electrode sheet, and then inject 0.1 ml of the prepared electrolyte to obtain the LiNi 0.8 Co 0.1 Mn 0.1 O2 battery.

[0094] LiNi 0.8 Co 0.1 Mn 0.1 The LiNi

[0095] O2 battery is conventionally charged for the first time as follows: constant current charging at 0.05C for 180 min, constant current charging at 0.2C until 4.35V, secondary vacuum sealing, and then further constant current charging at 0.2C until 4.4V. After standing at room temperature for 24 hr, constant current discharging at 0.2C until 3.0V.

[0095] II. Battery performance testing

[0096] (1) Thermal stability testing:

[0097] Cut the obtained composite separator into a 2 cm × 2 cm square, measure the area of the composite separator after placing it at 60°C for 30 min, and compare it with the initial area to calculate the percentage of the area of the composite separator after heat treatment to the initial area. The calculation formula is as follows:

[0098]

[0099] Among them, S1 is the initial area; S2 is the area after heating for 1 hour;

[0100] (2) High-temperature cycle performance testing

[0101] The obtained battery is placed in an oven at a constant temperature of 45 °C and charged at a constant current of 1C until 4.4V, then charged at a constant voltage until the current drops to 0.02C, and then discharged at a constant current of 1C until 3.0V. Cycle in this way, record the discharge capacity of the first time and the last time, and calculate the capacity retention rate of high-temperature cycle according to the following formula:

[0102] Capacity retention rate (%) = Discharge capacity of the last time / Discharge capacity of the first time × 100%.

[0103] Examples 14 - 18

[0104] Examples 14 - 18 are used to illustrate the secondary battery disclosed by the present invention, including most of the operation steps in Example 13, and the differences are as follows:

[0105] During the thermal stability test, the prepared composite separator is respectively placed at the temperatures shown in Examples 14 - 18 of Table 3 for heating. The anti-thermal shrinkage diagrams of the composite separator at different temperatures are shown in Figure 4 . The thermal stability test results of the composite separator are filled into Table 3.

[0106] Comparative Examples 4 - 9

[0107] Comparative Examples 4 - 9 are used to illustrate the secondary battery disclosed by the present invention, including most of the operation steps in Example 13, and the differences are as follows:

[0108] For Comparative Examples 4 - 9, the selected separator is only a conventional single-layer PP separator; and,

[0109] During the thermal stability test, the single-layer PP separator is respectively placed at the temperatures shown in Comparative Examples 4 - 9 of Table 3 for heating. The anti-thermal shrinkage diagrams of the single-layer PP separator at different temperatures are shown in Figure 4 . The thermal stability test results of the single-layer PP separator are filled into Table 3.

[0110] Examples 19 - 20

[0111] Examples 19 - 20 are used to illustrate the secondary battery disclosed by the present invention, including most of the operation steps in Example 13, and the differences are as follows:

[0112] During the preparation process of the composite separator, inorganic materials shown in Examples 19 - 20 of Table 4 are respectively added. The high-temperature cycle performance test results of the secondary battery made from the composite separator are filled into Table 4.

[0113] Example 21

[0114] Example 21 is used to illustrate the secondary battery disclosed by the present invention, including most of the operation steps in Example 13, and the differences are as follows:

[0115] The separator of Example 21 is a double-layer composite separator, and its preparation method is as follows:

[0116] Step 1: Preparation of inorganic mixed slurry: Weigh 400 mg of binder PVDF-HFP and 600 mg of Li4W 0.9 Mo 0.1 O5 inorganic particles in a ratio of 2:3, and then add 3800 mg of NMP solvent dropwise. After stirring together for 24 h, an inorganic coating slurry is prepared;

[0117] Step 2: Coating of inorganic mixed slurry: Cut a polypropylene porous membrane with a length of 20 cm and a thickness of 25 μm and lay it flat on a coater. Then pour the evenly stirred inorganic coating slurry on one side, and control a 20-μm gauge doctor blade to evenly coat the slurry on the polypropylene porous membrane at a linear speed of 3 m / min. After coating, put it into a vacuum drying oven and vacuum dry it at 80 °C for 12 h. After taking it out, pour the evenly stirred inorganic coating slurry on the other side, and then coat the second side according to the above method to obtain a double-layer composite separator with Li4W 0.9 Mo 0.1 O5 as the coating. The test results of the thermal stability test of the double-layer composite separator are filled in Table 3, and the separator morphology and the test results of the high-temperature cycle performance of the secondary battery made from the double-layer composite separator are filled in Table 4.

[0118] Table 3

[0119]

[0120] Table 4

[0121]

[0122] Combined with Tables 3-4, Appendix Figure 4-6 and Examples 13-21 and Comparative Examples 4-9, it can be seen that, first of all, Table 3 shows the thermal stability test data of single-layer composite separators containing inorganic materials and some double-layer composite separators, as well as the comparative data of the thermal stability test of single-layer PP separators without the inorganic materials. Combining Figure 4 with the data in Table 3, it can be seen that the thermal stability of single-layer composite separators and double-layer composite separators containing inorganic materials is significantly better than that of single-layer PP separators. The composite separator and / or double-layer composite separator is obtained by coating a coating containing inorganic materials on one side and / or both sides of the single-layer PP separator;

[0123] From Figure 4It can be seen that as the heating temperature of the single-layer PP separator increases, its shrinkage amplitude gradually increases, and the thermal shrinkage rate increases significantly. When the heating temperature rises to 160 °C, the thermal shrinkage rate of the single-layer PP separator is as high as 16.76%; while the thermal shrinkage rate of the single-layer composite separator containing the inorganic material described in this application rises slowly as the heating temperature gradually increases. When the heating temperature also rises to 160 °C, the thermal shrinkage rate of the single-layer composite separator containing the inorganic material is only 5.98%. Thus, it can be seen that coating the PP separator with the coating containing the inorganic material can significantly improve the thermal shrinkage resistance performance of the separator and the cycling performance of the battery.

[0124] At the same time, combined with Figure 5-6 It can be seen that the density of the composite separator coated with the inorganic material is much higher than that of the PP separator. At the same time, combined with the data in Table 4, it can be seen that although the thickness of the composite separator coated with the inorganic material is slightly thicker than that of the single-layer PP separator, the high-temperature cycling capacity retention rate of the secondary battery prepared therefrom is good, and the thermal shrinkage resistance is strong, which is beneficial to the long-term cycling use of the secondary battery and can effectively improve the service life of the secondary battery.

[0125] In summary, in the present invention, Mo is used to dope the existing Li4WO5 material. By doping the Li4WO5 material with Mo and strictly controlling the addition amount of Mo, the material composition and crystal lattice structure of the solid electrolyte are optimized to obtain an inorganic material with the chemical formula Li4W 1-x Mo x O5;

[0126] When the doped inorganic material is used to prepare a solid electrolyte, the density of the prepared solid electrolyte is greater than 90%. And when 0 < x ≤ 0.05, for the inorganic material with the chemical formula Li4W 1-x Mo x O5 obtained by doping Li4WO5 with Mo, the total conductivity of the solid electrolyte prepared therefrom can be increased by nearly 40 times compared with the total conductivity of the solid electrolyte prepared from the Li4WO5 material. Thus, it can be seen that using the inorganic material to prepare a solid electrolyte can significantly improve the density of the solid electrolyte and enhance the ionic conductivity of the solid electrolyte;

[0127] When the doped inorganic material is used to prepare an inorganic-organic composite solid electrolyte film, its total conductivity can be increased by 35 times, and the obtained inorganic-organic composite solid electrolyte film has good composite film ionic conductivity;

[0128] When the modified inorganic material is used to prepare the composite separator, the obtained composite separator has significantly better thermal stability than the single-layer PP separator. Moreover, when the heating temperature rises to 160 °C, the thermal shrinkage rate of the composite separator is only 5.98%. It can be seen that the composite separator prepared by the inorganic material has good thermal shrinkage resistance, and the density of the composite separator coated with the inorganic material is much higher than that of the PP separator;

[0129] When the solid electrolyte or the inorganic-organic composite solid electrolyte film and the composite separator are used to prepare a secondary battery, the obtained secondary battery has good high-temperature cycle capacity retention, strong thermal shrinkage resistance, and high ionic conductivity, which is beneficial to the long-term cyclic use of the secondary battery and can effectively improve the service life of the secondary battery.

[0130] The above further describes the present invention with the aid of specific embodiments. However, it should be understood that this specific description should not be construed as a limitation on the essence and scope of the present invention. Various modifications made by those of ordinary skill in the art to the above embodiments after reading this specification all fall within the scope protected by the present invention.

Claims

1. A solid electrolyte, characterized in that, The solid electrolyte includes an inorganic material, and the chemical formula of the inorganic material is: Li4W 1-x Mo x O5, where 0 < x ≤ 0.

5.

2. The solid electrolyte according to claim 1, wherein The solid electrolyte is an inorganic ceramic sheet or an inorganic-organic composite solid electrolyte film.

3. The solid electrolyte according to claim 2, wherein The solid electrolyte is an inorganic ceramic sheet with a thickness of 0.1 mm to 2 mm and a particle size of 200 nm - 50 μm.

4. The solid electrolyte according to claim 2, characterized in that The solid electrolyte is an inorganic-organic composite solid electrolyte film, and the inorganic-organic composite solid electrolyte film further includes a polymer matrix and a lithium salt. The mass percentage of the inorganic material in the inorganic-organic composite solid electrolyte film is 2% - 36%.

5. The solid electrolyte according to claim 4, wherein The polymer matrix is selected from one or more of poly(ethylene oxide)-based polymers, poly(vinyl acetate)-based polymers, poly(ethylene imine)-based polymers, poly(vinylidene fluoride)-based polymers, polyacrylonitrile-based polymers, and poly(methyl methacrylate)-based polymers. The mass percentage of the polymer matrix in the inorganic-organic composite solid electrolyte film is 38% - 69%. The lithium salt is selected from the group consisting of Li + as a cation and F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , AlO4 - , AlCl4 - , PF6 - , SbF6 - , AsF6 - , BF2C2O4 - , BC4O8 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , C4F9SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (F2SO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - , (CF3CF2SO2)2N - or more than one selected from any one of the groups as anions, and the mass percentage of the lithium salt in the inorganic-organic composite solid electrolyte film is 18% to 43%.

6. The solid electrolyte according to any one of claims 4 and 5, characterized in that, The thickness of the inorganic-organic composite solid electrolyte film is 5 μm to 200 μm, and the particle size of the inorganic material in the inorganic-organic composite solid electrolyte film is 20 nm - 50 μm.

7. A separator for a secondary battery, characterized in that, The separator includes a porous substrate and a porous layer laminated on at least one surface of the porous substrate. The porous layer contains an inorganic material, and the inorganic material is coated on the surface of the porous layer or blended inside the porous layer. The chemical formula of the inorganic material is: Li4W 1-x Mo x O5, where 0 < x ≤ 0.

5.

8. The separator for a secondary battery according to claim 7, wherein The mass percentage of the inorganic material in the porous layer is 60% - 95%.

9. A secondary battery, characterized in that, The secondary battery includes the solid electrolyte according to any one of claims 1 - 6 and / or the separator for a secondary battery according to any one of claims 7 - 8. The secondary battery is any one of a semi-solid battery, a quasi-solid battery, a all-solid-state battery, a lithium-ion battery, or a lithium battery.

10. Application of an inorganic material in improving the electrical conductivity, thermal shrinkage and thermal stability of a solid electrolyte, a separator for a secondary battery, and a secondary battery, characterized in that, The chemical formula of the inorganic material is: Li4W 1-x Mo x O5, where 0 < x ≤ 0.5.

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