Solid electrolyte, positive electrode sheet for secondary battery, and secondary battery

Abstract

To overcome the problem of large interface resistance and low ionic conductivity of the existing inorganic solid-state electrolyte, the application provides a solid-state electrolyte, which comprises an inorganic material having a NASICON type crystal structure with a chemical formula of: Li 1.3+x Al 0.3‑ x Mg x Ti 1.7 (PO4)3, 0

Description

Technical Field

[0001] This invention relates to the field of electrochemical technology, specifically to solid electrolytes, positive electrode sheets for secondary batteries, and secondary batteries. Background Technology

[0002] Currently, commercial lithium-ion batteries generally use organic liquid electrolytes, which are composed of electrolyte lithium salts and organic solvents. However, they have problems such as low ignition point, low flash point, and leakage. For example, many batteries use large liquid electrolyte storage tanks, where sulfide and polysulfide discharge products are dissolved and diffuse from the positive electrode, making them unusable for the next electrochemical reaction. This reduces battery capacity and also poses significant safety hazards.

[0003] Existing partially industrialized polymer electrolytes also suffer from poor low-temperature performance and inadequate high-power output capabilities. For example, linear or cross-linked polymers obtained by the olefinic oxygen polymerization reaction of ethylene oxide and propylene oxide are mainly used as ion-conducting polymers in solid polymer electrolytes. In lithium batteries using polymers synthesized from these monomers as the matrix, the strong interaction between the cross-linked network structure of the polymer matrix and the olefinic oxygen remaining in the matrix reduces the mobility of lithium ions. Therefore, the optimization and development of electrolyte materials have become the key to the application and promotion of lithium-ion batteries.

[0004] Li 1.3 Al 0.3 Ti 1.7 (PO4)3 (LATP) is an important inorganic material widely used in lithium-ion batteries, lithium batteries, and solid-state batteries. It belongs to the NASICON-type inorganic solid-state electrolyte material and has advantages such as low cost, simple preparation, and high ionic conductivity. However, when LATP is directly used as a solid-state electrolyte inorganic material, it suffers from drawbacks such as high grain boundary resistance and low ionic conductivity in the resulting inorganic ceramic sheets or composite solid-state electrolyte films. Furthermore, it exhibits slow chemical reactions with the Li metal anode, which is detrimental to long-term battery cycling. Therefore, developing an inorganic solid-state electrolyte with low grain boundary resistance and high ionic conductivity is urgently needed. Summary of the Invention

[0005] To solve the above-mentioned technical problems, the present invention provides a solid electrolyte, an electrode sheet for a secondary battery, and a secondary battery, by using a chemical formula of Li 1.3+x Al 0.3-x Mg x Ti 1.7An inorganic material of (PO4)3 (0 < x ≤ 0.05) is used as a bulk material to prepare a solid electrolyte, or the inorganic material with the aforementioned chemical formula is coated on the surface of the active material layer of the positive electrode sheet or blended inside the active material layer to optimize and improve the high-temperature cycle stability performance of the secondary battery to the greatest extent.

[0006] To achieve the above object, in the first aspect of the present invention, a solid electrolyte is provided. The solid electrolyte includes an inorganic material, and the inorganic material has a NASICON-type crystal structure with the chemical formula: Li 1.3+x Al 0.3-x Mg x Ti 1.7 (PO4)3, where 0 < x ≤ 0.05.

[0007] In the present invention, the inorganic material with the above chemical formula is used as a bulk material to prepare a solid electrolyte. At the same time, by restricting the crystal structure and unit cell parameters of the inorganic material, the grain boundary impedance is reduced; in the present invention, the existing inorganic material LATP is doped and modified, and the modified LATP-Mg inorganic material is used as the bulk material of the solid electrolyte to improve the ionic conductivity of the solid electrolyte, and the high-temperature cycle performance of the secondary battery can be optimized and improved to the maximum extent.

[0008] Further, the crystal structure has an R-3C space group, and its unit cell parameters are: And α = 90.000, β = 90.000, γ = 120.000.

[0009] Further, the average particle size of the inorganic material is 20 nm - 20 μm. Preferably, the average particle size of the inorganic material is 40 nm - 10 μm, and more preferably 40 nm - 500 nm.

[0010] Further, the solid electrolyte is an inorganic ceramic sheet or an inorganic-organic composite solid electrolyte film.

[0011] Further, the solid electrolyte is an inorganic ceramic sheet. Preferably, the thickness of the inorganic ceramic sheet is 10 μm - 2 mm, and more preferably 20 μm - 1 mm.

[0012] Further, the solid electrolyte is an inorganic-organic composite solid electrolyte film. The solid electrolyte further includes a polymer matrix, and 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;

[0013] Preferably, the polymer matrix accounts for 5% to 80% of the mass percentage of the solid electrolyte, more preferably 30% to 70%, and even more preferably 35% to 65%.

[0014] Furthermore, the solid electrolyte also includes a lithium salt, wherein the lithium salt is selected from Li + As cations and F - Cl - ,Br - I - NO 3- N(CN) 2- BF 4- ,ClO 4- AlO 4- AlCl 4- PF 6- 、SbF 6- AsF 6- BF2C2O 4- BC4O 8- (CF3)2PF 4- (CF3)3PF 3- (CF3)4PF 2- (CF3)5PF - (CF3)6P - CF3SO 3- C4F9SO 3- CF3CF2SO 3- (CF3SO2)2N - (F2SO2)2N - CF3CF2(CF3)2CO - (CF3SO2)2CH - CF3(CF2)7SO 3- CF3CO 2- CH3CO 2- SCN - (CF3CF2SO2)2N - Any one of them can be used as an anion.

[0015] Preferably, the lithium salt accounts for 40% to 80% of the mass percentage of the polymer in the solid electrolyte.

[0016] A second aspect of the present invention provides a positive electrode sheet for a secondary battery, comprising a positive electrode active material layer and an inorganic material, wherein the inorganic material is coated on the surface of the positive electrode active material layer or mixed into the interior of the positive electrode active material layer, and the inorganic material has a NASICON-type crystal structure and its chemical formula is:

[0017] Li1.3+x Al 0.3-x Mg x Ti 1.7 (PO4)3, where 0 < x ≤ 0.05.

[0018] Furthermore, the positive electrode active material layer includes a positive electrode active material selected from any one of nickel-cobalt-manganese ternary materials, LiMn2O4, LiNi 0.5 Mn 1.5 O4, LiCoO2, LiFePO4, sulfur, and their composites. The inorganic material is coated on the surface of the positive electrode active material or blended inside the positive electrode active material.

[0019] In the present invention, by coating an inorganic material with the chemical formula Li 1.3+x Al 0.3-x Mg x Ti 1.7 (PO4)3 (0 < x ≤ 0.05) on the surface of the positive electrode active material layer or blending it inside the positive electrode active material layer, the interfacial stability of the positive electrode active material layer during charge and discharge can be effectively improved, and the cycle performance of the secondary battery can be enhanced.

[0020] Furthermore, the crystal structure has an R-3C space group, and its unit cell parameters are: and α = 90.000°, β = 90.000°, γ = 120.000°.

[0021] In the third aspect of the present invention, a secondary battery is provided, which includes the aforementioned solid electrolyte and / or the aforementioned positive electrode sheet.

[0022] Furthermore, the secondary battery is any one of a semi-solid battery, a quasi-solid battery, a full-solid battery, a lithium-ion battery, or a lithium battery.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] In the present invention, Mg is used to modify the LATP inorganic material and the addition amount of Mg is strictly controlled to optimize the material composition and lattice structure of the solid electrolyte, thereby obtaining an inorganic material Li 1.3+x Al 0.3-x Mg x Ti 1.7(PO4)3(0 < x ≤ 0.05). The solid electrolyte prepared with the inorganic material as the bulk material has the advantages of high density and good conductivity, and can optimize and improve the high-temperature cycling performance of secondary batteries to the greatest extent. At the same time, the modified inorganic material LATP-Mg can also be coated on the surface of the active material layer of the positive electrode sheet or blended inside the active material layer, which can effectively improve the interfacial stability of the active material layer during charge and discharge and enhance the high-temperature cycling performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a schematic diagram of the crystal structure of the inorganic powder material prepared in the embodiment of the present invention;

[0026] Figure 2 is the XRD phase characterization spectrum of the inorganic material prepared in the embodiment of the present invention;

[0027] Figure 3 is the SEM image of the inorganic ceramic sheet prepared in the embodiment of the present invention;

[0028] Figure 4 is the conductivity data graph of the solid electrolyte prepared in the embodiment of the present invention at room temperature. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0029] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments in the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments in 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.

[0030] The present invention will be described in detail below through embodiments.

[0031] Example 1

[0032] (1) Preparation of solid electrolyte

[0033] LiOH·H2O powder, NH4H2PO4 powder, TiO2 powder, Al2O3 powder and MgO powder were added in masses of LiOH·H2O 1.458 g, NH4H2PO4 9.063 g, TiO2 3.537 g, Al2O3 0.331 g, and MgO 0.040 g respectively. An appropriate amount of ethanol solvent was added, and ball milling was carried out in a planetary ball mill at a rotation speed of 360 rpm for 4 h. Then the ball-milled powder was loaded into an alumina crucible and placed in a muffle furnace for calcination at 300 °C for 5 h and calcination at 900 °C for 5 h, and then cooled to obtain the chemical formula Li shown in Example 1 in Table 1 1.31 Al 0.29 Mg0.01 Ti 1.7 The inorganic material of (PO4)3 has an average particle size of 5 μm.

[0034] The inorganic material with an average particle size of 5 μm was further refined to D by secondary ball milling. V After the material is approximately 1-2 μm thick, it is rapidly sintered using the SPS (spark plasma sintering) method. After annealing at a certain temperature, it is polished with sandpaper to obtain an inorganic ceramic sheet as a solid electrolyte. The thickness of the inorganic ceramic sheet is approximately 1 mm.

[0035] (2) Preparation of positive electrode

[0036] The positive electrode active material LiFePO4, conductive carbon black Super-P, and binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 93:4:3, and then dispersed in N-methyl-2-pyrrolidone (NMP) to obtain a positive electrode slurry. The slurry is uniformly coated on both sides of an aluminum foil, dried, calendered, and vacuum dried, and then aluminum leads are welded on using an ultrasonic welder to obtain a positive electrode sheet with a thickness of 120-150 μm.

[0037] (3) Battery assembly

[0038] The positive electrode, solid electrolyte, and negative lithium metal prepared in this embodiment are assembled into a solid-state battery.

[0039] II. Performance Testing

[0040] (1) Crystal structure

[0041] The inorganic material Li obtained 1.31 Al 0.29 Mg 0.01 Ti 1.7 Crystal structure analysis was performed on (PO4)3, and the resulting schematic diagram is shown below. Figure 1 As shown.

[0042] (2) XRD phase characterization

[0043] The inorganic material Li obtained 1.31 Al 0.29 Mg 0.01 Ti 1.7 (PO4)3 was scanned using an X-ray diffractometer. X-ray (Cu) diffraction: voltage 40 kV, current 25 mA; scanning 2θ angle range 10–80°; continuous scanning mode; scanning speed 0.1 s / step; step size 0.02° / step. The resulting characterization spectrum is shown below. Figure 2 .

[0044] (3) Observation by scanning electron microscope (SEM)

[0045] Solid electrolytes are observed using SEM to obtain SEM images, such as... Figure 3 As shown.

[0046] (4) Ionic conductivity test

[0047] A gold film was sputtered onto both sides of the solid electrolyte to serve as conductive electrodes (blocking electrodes). The room-temperature AC impedance of the sample was then measured on an electrochemical workstation. The AC impedance was measured from a high frequency of 10 Hz. 6 From Hz to a low frequency of 0.1Hz, the total impedance value R of the electrolyte (including bulk resistance and grain boundary resistance, see...) is then obtained. Figure 4 The ionic conductivity of the inorganic ceramic sheet used as a solid electrolyte was tested at room temperature. The calculation formula is as follows:

[0048] σ = L / A·R;

[0049] Where L is the thickness of the solid electrolyte, A is the area of ​​the gold film, and R is the total resistance of the solid electrolyte.

[0050] (5) High-temperature cycling performance test

[0051] At 60°C, the assembled solid-state battery was charged to 3.8V with a constant current of 0.2C, and then discharged to 2.6V with a constant current of 0.2C. This cycle was repeated 200 times, and the discharge capacity of the first cycle and the discharge capacity of the last cycle were recorded.

[0052] Calculate the capacity retention during high-temperature cycling using the following formula:

[0053] Capacity retention rate % = Last discharge capacity / First discharge capacity × 100%.

[0054] Examples 2-5

[0055] Examples 2-5 illustrate the secondary battery disclosed in this invention, including most of the operating steps in Example 1, with the following differences:

[0056] In the preparation of the solid electrolyte, LiOH·H2O powder, NH4H2PO4 powder, TiO2 powder, Al2O3 powder, and MgO powder in different mass ratios were added to obtain inorganic materials with the chemical formulas shown in Examples 2-5 of Table 1. These inorganic materials were then used to prepare corresponding inorganic ceramic sheets. The ionic conductivity test results of the obtained inorganic ceramic sheets and the high-temperature cycle capacity retention results of secondary batteries made from the inorganic ceramic sheets are recorded in Table 1.

[0057] Comparative Examples 1-4

[0058] Comparative Examples 1-4 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:

[0059] During the preparation process of the solid electrolyte, LiOH·H2O powder, NH4H2PO4 powder, TiO2 powder, Al2O3 powder, and MgO powder with different mass ratios are used to obtain the inorganic materials with the chemical formulas shown in Comparative Examples 1-4 in Table 1, and the corresponding inorganic ceramic sheets are prepared from the inorganic materials. The ion conductivity test results of the obtained inorganic ceramic sheets and the high-temperature cycle capacity retention rate results of the secondary batteries made from the inorganic ceramic sheets are filled in Table 1.

[0060] Table 1

[0061]

[0062] Please refer to Figure 1 , which is a schematic diagram of the crystal structure of the inorganic powder material prepared in Example 1 of the present invention. It can be seen from the figure that Li 1.31 Al 0.29 Mg 0.01 Ti 1.7 (PO4)3 inorganic powder material has an R-3C space group, and its unit cell parameters are: and α = 90.000°, β = 90.000°, γ = 120.000°.

[0063] At the same time, combined with Figure 2 and the data of Examples 1-5 and Comparative Examples 1-4, it can be seen that within the range of 0 ≤ x ≤ 0.1, the inorganic materials with the chemical formula of Li 1.3+x Al 0.3-x Mg x Ti 1.7 (PO4)3 are all high-purity phases, and there are no impurity peaks in the XRD phase characterization spectrum.

[0064] Please refer to Figure 3 , which is the SEM image of the inorganic ceramic sheet prepared in Example 1. It can be seen from the figure that its density is greater than 90%. It can be seen that by modifying the existing LATP inorganic material with Mg, the density of the inorganic material can be significantly improved. Therefore, the grain boundary impedance can be effectively reduced.

[0065] Moreover, combined with Figure 4 and the data in Table 1, it can be clearly seen that when 0 < x < 0.05, the grain boundary conductivity of the inorganic material with the chemical formula of Li 1.3+ x Al 0.3-x Mg x Ti 1.7 (PO4)3, compared with the existing Li1.3 Al 0.3 Ti 1.7 (PO4)3 has a grain boundary conductivity that can be increased by 5 - 7 times, and the total conductivity of the inorganic ceramic sheet prepared therefrom can be increased by 1 time; when x = 0.05, it has Li 1.3+x Al 0.3-x Mg x Ti 1.7 The grain boundary conductivity of the inorganic material with the chemical formula of Li 1.3 Al 0.3 Ti 1.7 (PO4)3 is increased by 0.5 times compared to that of Li 1.3+x Al 0.3-x Mg x Ti 1.7 (PO4)3, and the total conductivity of the inorganic ceramic sheet prepared therefrom is increased by nearly 1 time; when 0.05 < x ≤ 0.1, although it has Li

[0066] In addition, it can be seen from the data in Table 1 that when 0 < x ≤ 0.05, for the solid-state battery prepared from the ceramic sheet of the inorganic material with the chemical formula of Li 1.3+x Al 0.3-x Mg x Ti 1.7 (PO4)3, the high-temperature cycle stability is good, and the capacity retention rate after 200 cycles at 60 °C can be as high as 87%, which is significantly higher than that of the LA TP inorganic material without Mg modification, and is beneficial to improving the long-term cycle life of the solid-state battery; while when 0.05 < x ≤ 0.1, for the solid-state battery prepared from the ceramic sheet of the inorganic material with the chemical formula of Li 1.3+x Al 0.3-x Mg x Ti 1.7 (PO4)3, the high-temperature cycle capacity retention rate is improved compared to that without Mg modification, but the improvement amplitude is not obvious, indicating that too much Mg modification is not conducive to improving the long-term cycle life of the solid-state battery.

[0067] Examples 6 - 8

[0068] Examples 6 - 8 are used to illustrate the solid-state battery disclosed in the present invention, including most of the operation steps in Example 1, and the differences are as follows:

[0069] During the preparation process of the solid-state electrolyte, the chemical formula Li 1.31 Al 0.29 Mg0.01 Ti 1.7 Inorganic materials of (PO4)3 were prepared by mixing polymer matrices and lithium salts with the contents shown in Examples 6-8 of Table 2. Specifically, the polymer matrix and lithium salts were mixed in a glove box. 1.31 Al 0.29 Mg 0.01 Ti 1.7 (PO4)3 powder and lithium salt were weighed in a certain proportion and mixed in an acetonitrile solution. After stirring for 24 hours, Li was obtained. 1.31 Al 0.29 Mg 0.01 Ti 1.7 A viscous slurry with uniformly dispersed (PO4)3 particles was coated onto a polytetrafluoroethylene (PTFE) plate. After the acetonitrile solvent had completely evaporated, a flexible, self-supporting inorganic-organic composite solid electrolyte film was obtained. The ionic conductivity test results of the obtained inorganic-organic composite solid electrolyte film and the high-temperature cycle capacity retention rate of the solid-state battery made from the inorganic-organic composite solid electrolyte film are filled in Table 2.

[0070] Comparative Example 5

[0071] Comparative Example 5 is used to illustrate the solid-state battery disclosed in this invention, including most of the operating steps in Example 1, except that:

[0072] In the preparation process of the solid electrolyte, the chemical formula Li obtained in Comparative Example 4 was used. 1.3 Al 0.3 Ti 1.7 Inorganic materials of (PO4)3 were prepared by mixing polymer matrix and lithium salt with the contents shown in Comparative Example 5 in Table 2. The specific process involved mixing the polymer matrix and Li in a glove box. 1.3 Al 0.3 Ti 1.7 (PO4)3 powder and lithium salt were weighed in a certain proportion and mixed in an acetonitrile solution. After stirring for 24 hours, Li was obtained. 1.3 Al 0.3 Ti 1.7 A viscous slurry with uniformly dispersed (PO4)3 particles was coated onto a polytetrafluoroethylene (PTFE) plate. After the acetonitrile solvent had completely evaporated, a flexible, self-supporting inorganic-organic composite solid electrolyte film was obtained. The ionic conductivity test results of the obtained inorganic-organic composite solid electrolyte film and the high-temperature cycle capacity retention rate of the solid-state battery made from the inorganic-organic composite solid electrolyte film are filled in Table 2.

[0073] Table 2

[0074]

[0075] As can be seen from Table 2, Examples 6-8 all involve using Li... 1.3+x Al 0.3-x Mg x Ti 1.7 Inorganic materials with the chemical formula (PO4)3 are mixed with different polymer matrices (e.g., polyvinyl oxide polymers) and different lithium salts (e.g., LiTFSI, LiClO4) to prepare Li-containing compounds. 1.3+x Al 0.3-x Mg x Ti 1.7 The inorganic-organic composite solid electrolyte film of (PO4)3 material exhibits twice the ionic conductivity of the composite solid electrolyte film of LATP material without Mg modification (Comparative Example 5); moreover, the Li-containing... 1.3+x Al 0.3-x Mg x Ti 1.7 The inorganic-organic composite solid electrolyte film of (PO4)3 material is used to prepare solid batteries. It has good high-temperature cycle stability. After 200 cycles at 60℃, the capacity retention rate can still be as high as 93%, which can significantly extend the long-term cycle life of solid batteries.

[0076] Therefore, it will contain Li 1.3+x Al 0.3-x Mg x Ti 1.7 Inorganic materials with the chemical formula (PO4)3 are mixed with different polymer matrices and / or different lithium salts to prepare inorganic-organic composite solid electrolyte films. All of these films exhibit higher composite membrane ionic conductivity. Furthermore, when these films are used to prepare corresponding solid batteries, the high-temperature cycle stability of the solid batteries is significantly improved, which is beneficial for extending the cycle life of secondary batteries.

[0077] Example 9

[0078] Example 9 illustrates the solid-state battery disclosed in this invention, including most of the operating steps in Example 1, except that:

[0079] In the preparation of solid electrolyte, the mass ratio of LiOH·H2O powder, NH4H2PO4 powder, TiO2 powder, Al2O3 powder and MgO powder is adjusted to obtain inorganic materials with the chemical formula shown in Comparative Example 4 in Table 1. The inorganic materials are then used to prepare corresponding inorganic ceramic sheets as solid electrolytes according to the method for solid electrolytes in Example 1.

[0080] During the preparation of the positive electrode, an appropriate amount of Li is added. 1.31 Al 0.29 Mg 0.01Ti 1.7 (PO4)3 powder is blended into the cathode active material LiFePO4, and is mixed with conductive carbon black Super-P and binder polyvinylidene fluoride (PVDF) to prepare a cathode sheet.

[0081] The capacity retention rate of the solid-state battery obtained in this embodiment after 200 high-temperature cycles is 80%, while the capacity retention rate of the solid-state battery in Comparative Example 4 after 200 high-temperature cycles is 75%. This shows that adding the Mg-modified LATP material to the cathode active material can effectively improve the interfacial stability of the active material layer during charge and discharge, and improve the high-temperature cycling performance of the battery.

[0082] In summary, the present invention uses Mg to modify the existing LATP material and strictly controls the addition amount of Mg to optimize the material composition and lattice structure of the solid electrolyte, and obtains an inorganic material with the chemical formula Li 1.3+x Al 0.3-x Mg x Ti 1.7 (PO4)3. When 0 < x < 0.05, the grain boundary conductivity of the inorganic material is increased by 5-7 times compared with the LATP material.

[0083] When the modified 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, the total conductivity of the prepared solid electrolyte can be increased by 1 time.

[0084] When the inorganic material with the chemical formula Li 1.3+x Al 0.3-x Mg x Ti 1.7 (PO4)3 (0 < x ≤ 0.05) is used to prepare an inorganic-organic composite solid electrolyte film, and its total conductivity can be increased by 1 time compared with the composite solid electrolyte film of the LATP material without Mg modification, and a composite solid electrolyte film with better ionic conductivity of the composite film is obtained;

[0085] When the modified inorganic material is used to prepare a cathode sheet for a secondary battery, the corresponding solid-state battery has good high-temperature cycling stability, and the capacity retention rate after 200 cycles at 60°C can reach 80%, which can effectively improve the interfacial stability of the active material layer during charge and discharge;

[0086] When the solid electrolyte or the inorganic-organic composite solid electrolyte film is used to prepare a secondary battery, the prepared secondary battery has a good high-temperature cycling capacity retention rate, which is beneficial to the long-term cycling use of the secondary battery and can effectively improve the service life of the secondary battery.

[0087] The present invention has been further described above with reference to specific embodiments. However, it should be understood that the specific description herein should not be construed as limiting the nature and scope of the present invention. Various modifications made to the above embodiments by those skilled in the art after reading this specification are all within the scope of protection of the present invention.

Claims

1. A solid electrolyte, characterized in that, The solid electrolyte is an inorganic ceramic sheet or an inorganic-organic composite solid electrolyte film. The solid electrolyte includes inorganic materials with a NASICON-type crystal structure and the chemical formula is: Li 1.3+x Al 0.3-x Mg x Ti 1.7 (PO4)3, where 0 < x ≤ 0.

05.

2. The solid electrolyte according to claim 1, characterized in that, The crystal structure has the R-3C space group and its cell parameters are: a = 8.4-8.6 Å, b = 8.4-8.6 Å, c = 20.5-21.1 Å, and α = 90.000º, β = 90.000º, γ = 120.000º.

3. The solid electrolyte according to claim 1, characterized in that, The average particle size of the inorganic material is 20 nm to 20 μm.

4. The solid electrolyte according to claim 1, characterized in that, The solid electrolyte is an inorganic ceramic sheet with a thickness of 10μm-2mm.

5. The solid electrolyte according to claim 1, characterized in that, The solid electrolyte is an inorganic-organic composite solid electrolyte film, and the solid electrolyte also includes a polymer matrix; The polymer matrix is ​​selected from one or more of the following: polyoxyethylene polymer, polyvinyl acetate polymer, polyethyleneimine polymer, polyvinylidene fluoride polymer, polyacrylonitrile polymer, and polymethyl methacrylate polymer. The polymer matrix accounts for 30% to 70% of the mass of the solid electrolyte.

6. The solid electrolyte according to claim 5, characterized in that, The solid electrolyte further includes a lithium salt, which is selected from Li. + As cations 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 - Any one of them can be used as an anion.

7. The solid electrolyte according to claim 6, characterized in that, The lithium salt accounts for 40% to 80% of the mass percentage of the solid electrolyte.

8. A positive electrode sheet for a secondary battery, characterized in that, It includes a positive electrode active material layer and an inorganic material, wherein the inorganic material is coated on the surface of the positive electrode active material layer or mixed into the interior of the positive electrode active material layer, and the inorganic material has a NASICON-type crystal structure and its chemical formula is: Li 1.3+x Al 0.3-x Mg x Ti 1.7 (PO4)3, where 0 < x ≤ 0.05; The positive electrode active material layer includes the positive electrode active material LiFePO4.

9. The positive electrode sheet for a secondary battery according to claim 8, characterized in that, The crystal structure has the R-3C space group and its cell parameters are: a = 8.4-8.6 Å, b = 8.4-8.6 Å, c = 20.5-21.1 Å, and α = 90.000º, β = 90.000º, γ = 120.000º.

10. A secondary battery, characterized in that, The secondary battery comprises a solid electrolyte as described in any one of claims 1-7 and / or a positive electrode as described in any one of claims 8-9; The secondary battery is any one of a semi-solid-state battery, a quasi-solid-state battery, an all-solid-state battery, a lithium-ion battery, or a lithium battery.

Images