Solid-state electrolyte, method for preparing the same, and secondary battery

Abstract

The application belongs to the technical field of secondary batteries, and particularly relates to a solid-state electrolyte, a preparation method thereof and a secondary battery. 3+x M2PA4P2O7, wherein x is 0-0.3, M is at least one of Fe, Al and Ti, and A is at least one of O, S and Se. The solid-state electrolyte has good structural stability and high conductivity.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of secondary batteries, and particularly relates to a solid-state electrolyte, a preparation method thereof and a secondary battery. BACKGROUND

[0002] Lithium ion batteries have been widely used in digital products, power and energy storage fields. Currently, commercial lithium ion batteries mainly use liquid electrolyte, which has problems such as easy volatilization, easy corrosion, easy flammability, easy explosion and poor thermal stability. In the use process, thermal runaway may easily occur, thereby causing safety problems. Solid-state lithium ion batteries use solid electrolyte to replace liquid electrolyte, which can fundamentally solve the safety problem of lithium ion batteries.

[0003] In the currently used solid-state electrolyte, the room temperature conductivity of the polymer solid-state electrolyte is poor, the chemical stability of the sulfide solid-state electrolyte is poor, and it is difficult to be applied in industrialization. The chemical stability of the oxide is the best, and the ionic conductivity is not high. Therefore, there is an urgent need for a solid-state electrolyte which has both structural stability and high ionic conductivity. SUMMARY

[0004] One of the purposes of the application is to provide a solid-state electrolyte with good structural stability and high ionic conductivity in view of the deficiencies of the prior art.

[0005] In order to achieve the above purpose, the application adopts the following technical scheme:

[0006] A solid-state electrolyte, the chemical formula of which is Li 3+x M2PA4P2O7, wherein the value of x is 0-0.3, M is at least one of Fe, Al and Ti, and A is at least one of O, S and Se.

[0007] Preferably, the ionic conductivity of the solid-state electrolyte is 10 -5 S / cm-8*10 -3 S / cm, and the electrochemical stability window of lithium is 0.1V-6V.

[0008] The second purpose of the application is to provide a preparation method of a solid-state electrolyte, which is simple to operate and can be mass-produced in view of the deficiencies of the prior art.

[0009] In order to achieve the above purpose, the application adopts the following technical scheme:

[0010] A preparation method of a solid-state electrolyte, comprising the following steps:

[0011] Step S1, a lithium source, a first doping element source material, a second doping element source material and a phosphoric acid radical containing source material are mixed in a molar ratio, and ball milling is performed under an inert environment to obtain a mixed powder;

[0012] Step S2, the mixed powder is heated and calcined under inert environment to obtain a solid electrolyte.

[0013] Preferably, the weight ratio of the lithium source, the first doping element source material, the second doping element source material and the phosphate-containing source material is 1-3:1-5:0.1-2:1-5.

[0014] Preferably, the first doping element source material comprises at least one of FeO, Fe2O3, Fe3O4, Al2O3 and TiO2.

[0015] Preferably, the second doping element source material comprises at least one of P2O5, P2S5, S and SeO2.

[0016] Preferably, the phosphate-containing source material comprises at least one of FePO4, AlPO4, K2HPO4 and KH2PO4.

[0017] Preferably, the ball milling time in step S1 is 8-45h, and the ball milling rotation speed is 600-3000rpm / min.

[0018] Preferably, the calcination temperature in step S2 is 600-1200℃, and the calcination time is 4-25h.

[0019] The third object of the present application is to provide a secondary battery with good structural stability and high ionic conductivity.

[0020] In order to achieve the above object, the present application adopts the following technical scheme:

[0021] A secondary battery comprises the solid electrolyte described above.

[0022] Compared with the prior art, the present application has the beneficial effects that the solid electrolyte of the present application has metal element doping and non-metal element doping, forms a NASICON structure with high ionic conductivity, and also has good structural stability. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is the XRD pattern of the solid electrolyte of Example 1, Example 10 and Example 11 of the present application. DETAILED DESCRIPTION

[0024] The present application will be further described in detail below in conjunction with the specific embodiments and the accompanying drawings of the specification, but the embodiments of the present application are not limited thereto.

[0025] A solid electrolyte, whose chemical general formula is Li 3+xM2PA4P2O7, wherein x is 0-0.3, M is at least one of Fe, Al, Ti, and A is at least one of O, S, and Se.

[0026] The solid electrolyte of the present application contains both PO4 and P2O7 phosphorus configurations, uses a first doping element M to connect the PO4 and P2O7 phosphorus configurations to each other to form a NASICON structure, and then uses a second doping element A to adjust the size of the PA4 unit and thus the ion channel, thereby improving the ionic conductivity and obtaining the solid electrolyte of the present application which has both high ionic conductivity and good structural stability.

[0027] Preferably, the ionic conductivity of the solid electrolyte is 10 -5 S / cm-8*10 -3 S / cm, and the electrochemical stability window for lithium is 0.1V-6V. The solid electrolyte of the present application has high ionic conductivity, good electrochemical performance, and a lithium electrochemical stability window of 0.1V-6V, good inclusivity, high tolerance for different contents and different elements, and very wide element adjustability.

[0028] A preparation method of a solid electrolyte, comprising the following steps:

[0029] In step S1, a lithium source, a first doping element source material, a second doping element source material, and a phosphoric acid source material are mixed in a molar ratio and ball milled in an inert environment to obtain a mixed powder;

[0030] In step S2, the mixed powder is heated and calcined in an inert environment to obtain the solid electrolyte.

[0031] The preparation method of the solid electrolyte of the present application is simple to operate and can be mass-produced. In the present application, the lithium source, the first doping element source material, the second doping element source material, and the phosphoric acid source material are mixed in the ball milling process, so that the raw materials are fully mixed, and then heated and calcined to obtain the solid electrolyte of the present application. The inert environment uses one or more of nitrogen and argon. The inert environment can avoid the entry of air during ball milling or calcination, thereby preventing the generation of impurities and ensuring the reaction.

[0032] Preferably, the weight ratio of the lithium source, the first doping element source material, the second doping element source material, and the phosphoric acid source material is 1-3:1-5:0.1-2:1-5. The weight ratio of the lithium source, the first doping element source material, the second doping element source material, and the phosphoric acid source material is 1:2:0.3:2, 2:2:0.5:3, 1:2:1.5:4, 3:5:1:1, 2:4:2:4, 3:4:2:5, 3:4:2:5, or 3:2:1.5:4.

[0033] Preferably, the first doped element source material comprises at least one of FeO, Fe2O3, Fe3O4, Al2O3, TiO2. The first doped element source material has a metal element, which can connect two different phosphorus element structures, thereby forming a stable NASICON structure, thereby improving the structural stability of the solid-state electrolyte.

[0034] Preferably, the second doped element source material comprises at least one of P2O5, P2S5, S, SeO2. The second doped element source material is a non-metal element, which can form a phosphorus-like ion with phosphorus, and the phosphorus-like ion has a different size, thereby adjusting the ion channel of the material, thereby changing the ionic conductivity.

[0035] Preferably, the phosphate-containing source material comprises at least one of FePO4, AlPO4, K2HPO4, KH2PO4. The phosphate-containing source material can be selected to contain the first doped element, which can provide the first doped element while avoiding the introduction of new impurities.

[0036] Preferably, the ball milling time in step S1 is 8-45h, and the ball milling rotation speed is 600-3000rpm / min. The ball milling time in step S1 is 8-10h, 10-20h, 20-30h, 30-40h, 40-45h, and specifically, the ball milling time is 8h, 10h, 12h, 15h, 17h, 20h, 22h, 25h, 27h, 30h, 32h, 35h, 37h, 40h, 45h. Preferably, the ball milling rotation speed is 600-1000rpm / min, 1000-2000rpm / min, 2000-3000rpm / min, and specifically, the ball milling rotation speed is 600rpm / min, 800rpm / min, 900rpm / min, 1000rpm / min, 1300rpm / min, 1500rpm / min, 1700rpm / min, 2000rpm / min, 2500rpm / min, 3000rpm / min, 3500rpm / min.

[0037] Preferably, the calcination temperature in step S2 is 600-1200℃, and the calcination time is 4-25h. Preferably, the calcination temperature in step S2 is 600-800℃, 800-1000℃, 1000-1200℃, and specifically, the calcination temperature is 600℃, 700℃, 800℃, 900℃, 1000℃, 1100℃, 1200℃. The calcination time is 4-10h, 10-20h, 20-25h, and specifically, the calcination time is 4h, 8h, 10h, 15h, 20h, 25h.

[0038] A secondary battery has good structural stability and high ionic conductivity.

[0039] A secondary battery includes the solid electrolyte.

[0040] The solid electrolyte of the present application has metal element doping and non-metal element doping, forms a NASICON structure with high ionic conductivity, and also has good structural stability.

[0041] Example 1

[0042] A preparation method of a solid electrolyte includes the following steps:

[0043] (1) Lithium carbonate, Fe2O3, P2O5 and K2HPO4 with a molar ratio of 1.5:2:1:2 are ball-mixed, the ball-milling time is 12 hours, and the ball-milling atmosphere is Ar gas;

[0044] (2) The mixed powder is transferred to a tube furnace for calcination, the temperature is 750 degrees, the holding time is 8 hours, the heating rate is 2 degrees / min, the cooling rate is 1 degree / min, the gas flow rate is 70 cc / min, and the final product is Li3Fe2PO4P2O4 with a NASICON structure. The XRD pattern is shown in Figure 1 .

[0045] Preparation of the positive electrode sheet: lithium cobaltate, conductive agent super carbon (Super-P), and binder polyvinylidene fluoride (PVDF) are uniformly mixed in a mass ratio of 97:1.5:1.5 to form a lithium ion battery positive electrode slurry with a certain viscosity, the slurry is coated on the current collector aluminum foil, and after drying at 85°C, cold pressing is performed; then edge cutting, sheet cutting, and striping are performed, and after striping, drying is performed at 110°C under vacuum conditions for 4 hours, and the tab is welded to form a lithium ion battery positive electrode sheet.

[0046] Preparation of the negative electrode sheet: graphite, conductive agent super carbon (Super-P), thickening agent sodium carboxymethyl cellulose (CMC), and binder styrene butadiene rubber (SBR) are mixed to form a slurry in a mass ratio of 96:2.0:1.0:1.0, which is coated on the current collector copper foil and dried at 85°C, then edge cutting, sheet cutting, and striping are performed, and after striping, drying is performed at 110°C under vacuum conditions for 4 hours, and the tab is welded to form a lithium ion battery negative electrode sheet.

[0047] Preparation of a lithium ion battery:

[0048] The positive electrode sheet, the solid electrolyte, and the negative electrode sheet are wound or stacked into an electric core, the solid electrolyte is located between the positive electrode sheet and the negative electrode sheet, the positive electrode is point-welded with an aluminum tab for lead-out, and the negative electrode is point-welded with a nickel tab for lead-out; then the electric core is placed in an aluminum plastic packaging bag, the above-mentioned electrolyte is injected, and after packaging, formation, capacity, and other processes, a lithium ion battery is prepared.

[0049] Example 2

[0050] The difference from Example 1 is that the molar ratio of the lithium source, the first dopant element source material, the second dopant element source material, and the phosphate ion-containing source material is 2:2:1:2.

[0051] The rest is the same as Example 1, which will not be repeated here.

[0052] Example 3

[0053] The difference from Example 1 is that the molar ratio of the lithium source, the first dopant element source material, the second dopant element source material, and the phosphate ion-containing source material is 3:2:1:2.

[0054] The rest is the same as Example 1, which will not be repeated here.

[0055] Example 4

[0056] The difference from Example 1 is that the molar ratio of the lithium source, the first dopant element source material, the second dopant element source material, and the phosphate ion-containing source material is 1:2:1:2.

[0057] The rest is the same as Example 1, which will not be repeated here.

[0058] Example 5

[0059] The difference from Example 1 is that the molar ratio of the lithium source, the first dopant element source material, the second dopant element source material, and the phosphate ion-containing source material is 1.5:2:1:4.

[0060] The rest is the same as Example 1, which will not be repeated here.

[0061] Example 6

[0062] The difference from Example 1 is that the molar ratio of the lithium source, the first dopant element source material, the second dopant element source material, and the phosphate ion-containing source material is 1.5:4:0.2:2.

[0063] The rest is the same as Example 1, which will not be repeated here.

[0064] Example 7

[0065] The difference from Example 1 is that the molar ratio of the lithium source, the first dopant element source material, the second dopant element source material, and the phosphate ion-containing source material is 1.5:1:2:2.

[0066] The rest is the same as Example 1, which will not be repeated here.

[0067] Example 8

[0068] The difference from Example 1 is that the first dopant element source material is Ti02.

[0069] The rest is the same as Example 1, which will not be repeated here.

[0070] Example 9

[0071] The difference from Example 1 is that the first dopant element source material is Al203.

[0072] The rest is the same as Example 1, which will not be repeated here.

[0073] Example 10

[0074] The difference from Example 8 is that the second dopant element source material is P2S5. The XRD curve is shown in Figure 1 .

[0075] The rest is the same as Example 8, which will not be repeated here.

[0076] Example 11

[0077] The difference from Example 10 is that the second dopant element source material is a mixture of P205 and P2S5 in a molar ratio of 1:1. The XRD curve is shown in Figure 1 .

[0078] The rest is the same as Example 10, which will not be repeated here.

[0079] Example 12

[0080] The difference from Example 10 is that the ball milling time in step S1 is 18 hours.

[0081] The rest is the same as Example 10, which will not be repeated here.

[0082] Example 13

[0083] The difference from Example 12 is that the calcination temperature in step S2 is 600°C, and the holding time is 4 hours.

[0084] The rest is the same as Example 12, which will not be repeated here.

[0085] Example 14

[0086] The difference from Example 12 is that the gas flow rate in the inert environment is 100 cc / min.

[0087] The rest is the same as Example 12, which will not be repeated here.

[0088] Example 15

[0089] The difference from Example 14 is that the calcination temperature is 1100℃, the heating rate is 1 degree / min, and the cooling rate is 0.5 degree / min.

[0090] The rest is the same as Example 14, which will not be repeated here.

[0091] Comparative Example 1

[0092] The difference from Example 1 is that there is no first doping element source material in step S1.

[0093] The rest is the same as Example 1, which will not be repeated here.

[0094] Comparative Example 2

[0095] The difference from Example 1 is that there is no second doping element source material in step S1.

[0096] The rest is the same as Example 1, which will not be repeated here.

[0097] Comparative Example 3

[0098] The difference from Example 1 is that there is no first doping element source material and no second doping element source material in step S1.

[0099] The rest is the same as Example 1, which will not be repeated here.

[0100] The secondary batteries prepared in Examples 1-15 and Comparative Examples 1-3 above are tested for ion conductivity and cycle capacity retention rate performance, and the test results are recorded in Table 1.

[0101] Table 1

[0102]

[0103] From the above Table 1, it can be concluded that the solid-state electrolyte of the present application has better structural stability and better ion conductivity than the prior art solid-state electrolyte, with an ion conductivity of 0.912 mS / cm and a cycle capacity retention rate of 89%.

[0104] From Examples 1-7, it can be concluded that when the molar ratio of the lithium source, the first doping element source material, the second doping element source material, and the phosphoric acid salt-containing source material is 2:2:1:2, the prepared secondary battery has better performance, better ion conductivity, and higher cycle capacity retention rate. When the content of lithium source is increased, the ion conductivity can be improved, but too high content of lithium source will lead to difficulty in synthesizing pure phase, and impurities such as Li2CO3 will appear, thereby affecting the structural stability and ion conductivity.

[0105] From the comparison of Examples 1, 8 and 9, it is found that when the first doping element source material is set as aluminum, the prepared secondary battery has better ionic conductivity and higher cycle capacity retention rate.

[0106] From the comparison of Examples 1, 10 and 11, it is found that when the second doping element source material is set as a mixture of P2O5 and P2S5 with a molar ratio of 1:1, the prepared secondary battery has better ionic conductivity and higher cycle capacity retention rate. When the second doping element source material includes P2O5 and P2S5, they have different sizes, which helps to form ion channels and improve ionic conductivity.

[0107] From the comparison of Examples 1, 12, it is found that when the ball milling time in the preparation process is set as 18 hours, the prepared secondary battery has better ionic conductivity and higher capacity retention rate.

[0108] From the comparison of Examples 1, 13 and 15, it is found that when the calcination temperature in the preparation process is controlled as 600℃ and the holding time is 4 hours, the prepared secondary battery has better ionic conductivity and better capacity retention rate.

[0109] From the comparison of Examples 1, 14, it is found that when the gas flow rate in the inert environment in the preparation process is set as 100cc / min, the prepared secondary battery has better ionic conductivity and better capacity retention rate.

[0110] Based on the disclosure and teachings of the above specification, a person of ordinary skill in the art will be able to make alterations and modifications to the above embodiments. Therefore, the present application is not limited to the specific embodiments described above, and any obvious improvements, replacements or modifications made by those skilled in the art based on the present application shall fall within the scope of the present application. In addition, although some specific terms are used in the specification, these terms are only for convenience of description and do not constitute any limitation on the present application.

Claims

1. A method of preparing a solid-state electrolyte, characterized by, The chemical formula of the solid-state electrolyte is Li 3+ x M2PA4P2O7, wherein x is 0-0.3, M is Ti, and A is O and S; the M connects the two phosphorus configurations of PA4 and P2O7 to form a NASICON structure, and the A is used to adjust the size of the PA4 unit; The preparation method of the solid-state electrolyte comprises the following steps: Step S1, mixing a lithium source, a first doping element source material, a second doping element source material, and a phosphate-containing source material according to a molar ratio, and ball milling under an inert environment to obtain a mixed powder; Step S2, heating and calcining the mixed powder under an inert environment to obtain a solid-state electrolyte; The first doping element source material is TiO2, and the second doping element source material is a mixture of P2O5 and P2S5 in a molar ratio of 1:

1.

2. The method of claim 1, wherein the solid-state electrolyte is prepared by a method comprising: The solid-state electrolyte has an ionic conductivity of 10 -5 S / cm~8*10 -3 S / cm, and an electrochemical stability window for lithium of 0.1V~6V.

3. The method of claim 1, wherein the solid-state electrolyte is prepared by a method comprising: The molar ratio of the lithium source, the first doping element source material, the second doping element source material, and the phosphate-containing source material is 1-3:1-5:0.1-2:1-5.

4. The method of claim 1, wherein the solid-state electrolyte is prepared by a method comprising: The phosphate-containing source material comprises at least one of K2HPO4 and KH2PO4.

5. The method of claim 1, wherein the solid-state electrolyte is prepared by a method comprising: The ball milling time in step S1 is 8-45 h, and the ball milling rotation speed is 600-3000 rpm / min.

6. The method of claim 1, wherein the solid-state electrolyte is prepared by a method comprising: The calcining temperature in step S2 is 600-1200 DEG C, and the calcining time is 4-25 h.

7. A secondary battery characterized by comprising: The solid-state electrolyte prepared by the preparation method of any one of claims 1-6.

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