Sulfide solid electrolyte and all-solid-state lithium battery

Abstract

The invention relates to the technical field of electrochemistry, and provides a sulfide solid electrolyte and an all-solid-state lithium battery, the chemical formula of the sulfide solid electrolyte is Li7-4x-yPMxS6-2x-yO2xXy, M is at least one of variable valence rare earth elements Ce, Eu, Pr and Sm, X is at least one of halogens, x is more than or equal to 0.005 and less than or equal to 0.3, y is more than or equal to 0.5 and less than or equal to 2, and the molar ratio of the element M to the element O is 1: 2. The Li site of the sulfide solid electrolyte is doped with the variable valence rare earth element M, the S site of the sulfide solid electrolyte is doped with the element O, and the molar ratio of the element M to the element O is regulated to be 1: 2, so that the structural stability of the sulfide solid electrolyte in a complex electrochemical environment is improved, and the chemical degradation behavior of the sulfide solid electrolyte in the cycle process is favorably inhibited; and meanwhile, the air stability and the ionic conductivity of the sulfide solid electrolyte are also improved, so that the cycle life and the reliability of the all-solid-state lithium battery are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrochemistry, in particular to a sulfide solid electrolyte and a full solid-state lithium battery. BACKGROUND

[0002] The sulfide solid electrolyte is considered as one of the core materials of the next generation full solid-state lithium battery due to its excellent ion conductivity and flexible mechanical properties. However, the sulfide solid electrolyte is easily affected by interface side reactions, structural degradation and electrochemical oxidation-reduction environment fluctuations during long-term charge-discharge cycling of the battery, resulting in unstable material structure, increased interface impedance and ultimately limiting the battery life and cycle stability. Especially under high voltage or high current density working conditions, the sulfur component in the electrolyte is prone to oxidation or migration, forming a non-lithium ion conductive side phase, which significantly deteriorates the performance of the full solid-state lithium battery. In addition, the sulfide solid electrolyte is extremely easy to decompose in air and will generate harmful gases such as hydrogen sulfide after contacting with moisture or oxygen, accompanied by significant structural damage and electrochemical performance decline. This air stability defect greatly limits the reliability of the sulfide solid electrolyte in industrial production, storage and transportation and actual application.

[0003] Therefore, how to improve the structural stability of the sulfide solid electrolyte in a complex electrochemical environment, inhibit its chemical degradation behavior during the cycle process, and improve the air stability of the sulfide solid electrolyte is a key problem that needs to be solved to improve the cycle life and reliability of the full solid-state lithium battery. SUMMARY

[0004] The purpose of the present application is to provide a sulfide solid electrolyte and a full solid-state lithium battery to improve the structural stability of the sulfide solid electrolyte in a complex electrochemical environment, inhibit its chemical degradation behavior during the cycle process, and improve the air stability and ion conductivity of the sulfide solid electrolyte, thereby improving the cycle life and reliability of the full solid-state lithium battery. The specific technical solutions are as follows:

[0005] The first aspect of the present application provides a sulfide solid electrolyte with a chemical formula of Li 7-4x-y PM x S 6-2x- y O 2x X y , M is at least one of variable valence rare earth elements Ce, Eu, Pr and Sm, X is at least one of halogens, 0.005≤x≤0.3, 0.5≤y≤2, and the molar ratio of M elements to O elements is 1:2.

[0006] In an embodiment of the present application, 0.02≤x≤0.15, 1.25≤y≤1.75.

[0007] In an embodiment of the application, X is at least one of Cl, Br and I.

[0008] In an embodiment of the application, the sulfide solid-state electrolyte has the chemical formula Li 7-4x-y PM x S 6-2x- y O 2x X’ 0.7y X’’ 0.3y , each of X’, X’’ is independently Cl, Br or I, and X’ is different from X’’.

[0009] In an embodiment of the application, the sulfide solid-state electrolyte has the chemical formula Li 7-4x-y PM x S 6-2x- y O 2x Cl 0.7y Br 0.3y .

[0010] In an embodiment of the application, the sulfide solid-state electrolyte is Li 5.55 PCe 0.05 S 4.65 O 0.1 Cl 0.87 5Br 0.375 , Li 5.67 PCe 0.02 S 4.71 O 0.04 Cl 0.875 Br 0.375 , Li 5.05 PCe 0.05 S 4.15 O 0.1 Cl 1.225 Br 0.525 , Li 5.55 PEu 0.0 5S 4.65 O 0.1 Cl 0.875 Br 0.375 , Li 5.55 PPr 0.05 S 4.65 O 0.1 Cl 0.875 Br 0.375 , Li 5.55 PSm 0.05 S 4.65 O 0.1 Cl 0.875 Br 0.375 .

[0011] In an embodiment of the present application, the unit cell parameter of the sulfide solid-state electrolyte satisfies: a = b = c = 9.85 ~ 10 Å.

[0012] In an embodiment of the present application, the particle size of the sulfide solid-state electrolyte satisfies: 0.5 µm < D50 < 4 µm, 7 µm < D90 < 10 µm.

[0013] In an embodiment of the present application, the ionic conductivity of the sulfide solid-state electrolyte is > 5 mS / cm.

[0014] A second aspect of the present application provides a full solid-state lithium battery, which comprises a positive electrode, a negative electrode and the sulfide solid-state electrolyte of the first aspect of the present application.

[0015] Advantages of the present application:

[0016] The present application provides a sulfide solid-state electrolyte and a full solid-state lithium battery, the chemical formula of the sulfide solid-state electrolyte is Li 7-4x-y PM x S 6-2x-y O 2x X y , M is at least one of variable valence rare earth elements Ce, Eu, Pr and Sm, X is at least one of halogens, 0.005 ≤ x ≤ 0.3, 0.5 ≤ y ≤ 2, the molar ratio of M element to O element is 1:2. The Li site of the sulfide solid-state electrolyte is doped with variable valence rare earth element M, the S site is doped with O element, and the molar ratio of M element to O element is controlled to be 1:2, which improves the structural stability of the sulfide solid-state electrolyte in a complex electrochemical environment, is conducive to inhibiting its chemical degradation behavior in the cycle process, and also improves the air stability and ionic conductivity of the sulfide solid-state electrolyte, thereby improving the cycle life and reliability of the full solid-state lithium battery.

[0017] Of course, implementing any product or method of the present application does not necessarily require achieving all the advantages described above at the same time. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other embodiments can also be obtained by those skilled in the art based on these drawings.

[0019] Figure 1 The sulfide solid-state electrolyte (Li 5.55 PCe 0.05 S 4.65 O 0.1 Cl 0.875 Br0.375 X-ray diffraction pattern of the sulfide solid electrolyte (Li

[0020] Figure 2 X-ray diffraction pattern of the sulfide solid electrolyte (Li 5.55 PEu 0.05 S 4.65 O 0.1 Cl 0.875 Br 0.375 ) prepared in Example 9;

[0021] Figure 3 X-ray diffraction pattern of the sulfide solid electrolyte (Li 5.55 PPr 0.05 S 4.65 O 0.1 Cl 0.875 Br 0.375 ) prepared in Example 10;

[0022] Figure 4 X-ray diffraction pattern of the sulfide solid electrolyte (Li 5.55 PSm 0.05 S 4.65 O 0.1 Cl 0.875 Br 0.375 ) prepared in Example 11;

[0023] Figure 5 X-ray diffraction pattern of the sulfide solid electrolyte (Li 5.75 PS 4.75 Cl 0.875 Br 0.375 ) prepared in Comparative Example 5. DETAILED DESCRIPTION

[0024] The technical solutions in the present application will be described clearly and completely below in combination with the embodiments and drawings of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. All other embodiments obtained by those skilled in the art based on the present application belong to the scope of protection of the present application.

[0025] A first aspect of the present application provides a sulfide solid electrolyte with a chemical formula of Li 7-4x-y PM x S 6-2x- y O 2x X yM is at least one of the variable valence rare earth elements Ce, Eu, Pr and Sm, X is at least one of halogen, 0.005≤x≤0.3, 0.5≤y≤2, the molar ratio of M element to O element is 1:2; preferably, 0.02≤x≤0.15, 1.25≤y≤1.75. For example, x can be 0.005, 0.02, 0.01, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3 or a range between any two of them, and y can be 0.5, 1, 1.25, 1.5, 1.75, 2 or a range between any two of them.

[0026] The present application dopes at least one of the variable valence rare earth elements Ce, Eu, Pr and Sm at Li site and oxygen at S site of the sulfide solid electrolyte, i.e. the rare earth element cation and oxygen anion participate in the hetero-substitution reaction in the crystal structure, respectively partially replacing the lithium site (Li + ) and the sulfur site (S 2- ) in the crystal lattice, thereby introducing stable components with redox buffering capacity on the basis of maintaining the stability of the crystal structure. The rare earth cation has a larger radius and a higher valence, which can induce the formation of lithium-deficient regions and local charge rearrangement in the crystal after replacing Li + site, which helps to optimize the lithium ion migration path and inhibit the accumulation of structural stress caused by local lithium-rich or lithium-poor, thereby improving the structural integrity. The O 2- ion in the rare earth oxide partially replaces the S 2- site, which can enhance the bonding ability between Li-O, P-O and M-O, improve the chemical stability of the crystal framework, and effectively reduce the migration or oxidation behavior of sulfur in the battery cycle, delaying the structural degradation. In addition, the doping of variable valence rare earth elements has excellent reversible redox performance, which can dynamically absorb or release electrons during the battery charging and discharging process, thereby forming an electronic buffer zone inside the material, balancing the electrochemical environment fluctuations, inhibiting the interface side reaction, and delaying the structural degradation. This mechanism helps to stabilize the potential gradient of the electrolyte / electrode interface and maintain the interface integrity during long-term cycling. Through the synergistic effect of the above multiple mechanisms, the sulfide solid electrolyte material provided by the present application exhibits more excellent structural stability and interface compatibility during long-term cycling, significantly prolonging the service life of the all-solid-state lithium battery, and is especially suitable for all-solid-state lithium battery systems under high-voltage working conditions.

[0027] To further ensure the controllability and functionality of the doping effect, the present application limits the molar ratio of rare earth element M to oxygen element O to 1:2, i.e. one rare earth metal ion corresponds to two oxygen ions, thereby forming stable or type coordination structure units in the material. Through this ratio limitation, the The lattice expansion, impurity phase generation or anion site disorder caused by excessive introduction can also avoid the lack of stable coordination caused by the isolated existence of rare earth ions, thereby inducing conductivity decline or structural defect accumulation. Under the condition of the molar ratio, the rare earth-oxygen structure formed not only stably embeds in the electrolyte lattice, but also has a highly ordered local structure, which helps to improve the lattice rigidity and bonding energy, enhance the resistance of the sulfide solid electrolyte material to external thermal disturbance and electrochemical stress, thereby enhancing its structural stability. In addition, limiting the molar ratio of M element to O element to 1:2 can ensure that the rare earth element M forms a complete electronic buffer structure in the lattice, which can absorb excess electrons in the charging and discharging process with its reversible redox behavior, inhibit the accumulation of electric charges generated by the interface side reaction, thereby delaying the interface aging and maintaining the interface electrochemical stability. In contrast, if the molar ratio of M element to O element is unbalanced, it may not only cause rare earth enrichment and interfere with the lattice structure, but also cause the buffer structure to be unstable due to insufficient oxygen content, thereby weakening the overall performance of the material.

[0028] In addition, when the rare earth ions replace Li + , since the ionic radius of the rare earth ions is larger than that of Li + , it will cause significant expansion and distortion of the local lattice, which increases the diffusion path of lithium ions and may form wider ion migration channels in the local area, thereby reducing the diffusion energy barrier of lithium ions and directly improving the ionic conductivity. In addition, the rare earth element doped at the Li site has an important influence on the interface and air stability. The doping of rare earth elements can reduce the vacancy concentration of lithium sites, thereby reducing the chemical activity of the solid electrolyte when in contact with air and inhibiting the occurrence of decomposition reactions. At the same time, the variable valence property of the rare earth element allows it to form a stable passivation layer in the interface region, which can reduce the sensitivity of the sulfide to oxygen and water in the air, further reduce its side reactions with air or electrode materials, thereby slowing down the oxidative degradation of the material and improving the stability. In addition, the rare earth ions have variable oxidation states, which can reduce the water adsorption and reactivity of the material by introducing oxygen vacancies, thereby further improving its stability in a humid environment. This local regulation mechanism not only strengthens the ion migration ability of the electrolyte, but also significantly enhances its interface and environmental stability.

[0029] Therefore, the present application dopes the Li site of the sulfide solid electrolyte with a variable valence rare earth element M and the S site with an O element, and regulates the molar ratio of M element to O element to 1:2, which improves the structural stability of the sulfide electrolyte in a complex electrochemical environment, is conducive to inhibiting its chemical degradation behavior during cycling, and also improves the air stability and ionic conductivity of the sulfide solid electrolyte, thereby improving the cycle life and reliability of the all-solid-state lithium battery.

[0030] When x is less than the range of the present application, i.e. x < 0.005, the doping amount is too low to achieve the purpose of modification, and when x is greater than the range of the present application, i.e. x > 0.3, the doping amount is too high to destroy the crystal lattice structure of the material, the lithium ion transmission channel is destroyed, and at the same time, impurities cannot be doped into the crystal lattice, which makes the ionic conductivity of the material decrease rapidly; when y is less than the range of the present application, i.e. y < 0.5, the halogen content is too low, which makes the ionic conductivity of the material decrease significantly, and when y is greater than the range of the present application, i.e. y > 2, the halogen content is too high, which also destroys the crystal lattice structure of the material, making the ionic conductivity of the material decrease significantly.

[0031] In an embodiment of the present application, X is at least one of Cl, Br and I.

[0032] In an embodiment of the present application, the chemical formula of the sulfide solid-state electrolyte is Li 7-4x-y PM x S 6-2x- y O 2x X’ 0.7y X’’ 0.3y , X’ or X’’ is each independently Cl, Br or I, and X’ is different from X’’. By introducing two kinds of halogens into the sulfide solid-state electrolyte and regulating the molar ratio of the two kinds of halogens to be 7:3, the coexistence of the two halogens can optimize the bonding state between the grains in the sintering process, reduce the stress concentration and defect generation at the grain boundary, thereby reducing the grain boundary impedance. The synergistic effect of the two halogens can form a relatively dense and uniform grain boundary, which helps to inhibit the interface reaction and improve the continuity of the overall ion conduction path.

[0033] In an embodiment of the present application, the chemical formula of the sulfide solid-state electrolyte is Li 7-4x-y PM x S 6-2x- y O 2x Cl 0.7y Br 0.3y The sulfide solid-state electrolyte of the present application includes Cl element and Br element, and the molar ratio of Cl element and B element is regulated to be 7:3, and There is a difference in ionic radius between Cl The ionic radius of Cl is about 1.81 Å, The ionic radius of Br is about 1.96 Å), and under the ratio of 7:3, the larger radius of Br can be introduced moderately while ensuring that the crystal lattice structure does not be distorted, thereby relieving the stress in the crystal and maintaining the stability of the face-centered cubic structure. If the proportion of Br is too high, the excessive expansion of the crystal lattice will destroy the Li +Migrating channel; if the proportion of Br is too low, the electrochemical performance is not obviously improved, and research finds that 7:3 is a balance point considering structural stability and functional optimization. Therefore, by selecting the above sulfide solid electrolyte, the structural stability of the sulfide solid electrolyte in a complex electrochemical environment can be further improved, and the air stability and ionic conductivity of the sulfide solid electrolyte are also further improved, thereby further improving the cycle life and reliability of the all-solid-state lithium battery.

[0034] In an embodiment of the present application, the chemical formula of the sulfide solid electrolyte is Li 7-4x- y PCe x S 6-2x-y O 2x Cl 0.7y Br 0.3y , 0.02≤x≤0.15, 1.25≤y≤1.75. By doping Ce at the Li site and oxygen at the S site of the argyrodite LPSC solid electrolyte, and the numerical range of x and y being within the above range, the structural stability of the sulfide solid electrolyte in a complex electrochemical environment can be further improved, and the air stability and ionic conductivity of the sulfide solid electrolyte are also further improved, thereby further improving the cycle life and reliability of the all-solid-state lithium battery.

[0035] In an embodiment of the present application, the chemical formula of the sulfide solid electrolyte is Li 7-4x- y PEu x S 6-2x-y O 2x Cl 0.7y Br 0.3y , 0.02≤x≤0.15, 1.25≤y≤1.75. By doping Eu at the Li site and oxygen at the S site of the argyrodite LPSC solid electrolyte, and the numerical range of x and y being within the above range, the structural stability of the sulfide solid electrolyte in a complex electrochemical environment can be further improved, and the air stability and ionic conductivity of the sulfide solid electrolyte are also further improved, thereby further improving the cycle life and reliability of the all-solid-state lithium battery.

[0036] In an embodiment of the present application, the chemical formula of the sulfide solid electrolyte is Li 7-4x- y PPr x S 6-2x-y O 2x Cl 0.7y Br 0.3y0.02≤x≤0.15, 1.25≤y≤1.75. Doping Sm at Li site and oxygen at S site of argyrodite LPSC solid-state electrolyte, and the numerical range of x and y being within the above range, can further improve the structural stability of the sulfide solid-state electrolyte in a complex electrochemical environment, and further improve the air stability and ionic conductivity of the sulfide solid-state electrolyte, thereby further improving the cycle life and reliability of the all-solid-state lithium battery.

[0037] In an embodiment of the present application, the chemical formula of the sulfide solid-state electrolyte is Li 7-4x- y PSm x S 6-2x-y O 2x Cl 0.7y Br 0.3y 0.02≤x≤0.15, 1.25≤y≤1.75. Doping Sm at Li site and oxygen at S site of argyrodite LPSC solid-state electrolyte, and the numerical range of x and y being within the above range, can further improve the structural stability of the sulfide solid-state electrolyte in a complex electrochemical environment, and further improve the air stability and ionic conductivity of the sulfide solid-state electrolyte, thereby further improving the cycle life and reliability of the all-solid-state lithium battery.

[0038] In an embodiment of the present application, the chemical formula of the sulfide solid-state electrolyte is Li 5.55 PCe 0.05 S 4.65 O 0.1 Cl 0.87 5Br 0.375 , Li 5.67 PCe 0.02 S 4.71 O 0.04 Cl 0.875 Br 0.375 , Li 5.05 PCe 0.05 S 4.15 O 0.1 Cl 1.225 Br 0.525 , Li 5.55 PEu 0.0 5S 4.65 O 0.1 Cl 0.875 Br 0.375 , Li 5.55 PPr 0.05 S 4.65 O 0.1 Cl 0.875 Br 0.375 , Li 5.55 PSm 0.05 S4.65 O 0.1 Cl 0.875 Br 0.375 The above sulfide solid electrolyte is selected to have higher ionic conductivity, air stability and good structural stability.

[0039] In an embodiment of the present application, the unit cell parameter of the sulfide solid electrolyte satisfies: a = b = c = 9.85 ~ 10 Å. The unit cell parameter of the sulfide solid electrolyte of the present application is within the above range, and the lattice structure of the material itself can be well maintained, so that the sulfide solid electrolyte has high ionic conductivity.

[0040] In an embodiment of the present application, the particle size of the sulfide solid electrolyte satisfies: 0.5 µm < D50 < 4 µm, 7 µm < D90 < 10 µm. The particle size of the sulfide solid electrolyte of the present application is within the above range, so that the sulfide solid electrolyte has good processing performance.

[0041] In an embodiment of the present application, the ionic conductivity of the sulfide solid electrolyte is > 5 mS / cm. Preferably, the ionic conductivity of the sulfide solid electrolyte is > 6 mS / cm; more preferably, the ionic conductivity of the sulfide solid electrolyte is > 7 mS / cm; still more preferably, the ionic conductivity of the sulfide solid electrolyte is > 8 mS / cm. The sulfide solid electrolyte of the present application has high ionic conductivity while improving structural stability and air stability, and can improve the electrochemical performance of the all-solid-state lithium battery when applied to the all-solid-state lithium battery.

[0042] The preparation method of the sulfide solid electrolyte is not particularly limited in the present application, as long as the purpose of the present application can be achieved, for example, the preparation method of the sulfide solid electrolyte can include: mixing raw materials and a solvent under inert atmosphere protection to obtain a suspension; drying the suspension by reduced pressure distillation to obtain a solid electrolyte precursor mixture; sintering the solid electrolyte precursor mixture to obtain the sulfide solid electrolyte.

[0043] The types of raw materials and solvents are not particularly limited in the present application, as long as the purpose of the present application can be achieved, for example, the raw materials can be Li2S, P2S5, LiCl, LiBr and rare earth oxides (such as CeO2, PrO2, Sm2O3, Eu2O3), and the solvent can be n-hexane, benzene, toluene, cyclohexane, n-pentane, cyclopentane, dimethyl carbonate. Since the rare earth element M in the present application replaces the monovalent , the charge imbalance will be introduced, so the amount of is appropriately reduced in the design of raw materials to maintain overall charge balance and crystal structure stability. For example, while keeping the P and S components unchanged, the amount of , increasing the proportion of rare earth oxides, i.e. the rare earth element M can be guided to preferentially enter the lithium site without destroying frame unit.

[0044] The application does not particularly limit the amount of raw materials and solvents added, as long as the purpose of the application can be achieved. For example, the mass ratio of raw materials to solvent is 1:1-3. The application does not particularly limit the way of drying by vacuum distillation, as long as the purpose of the application can be achieved. For example, the temperature of drying by vacuum distillation is 40-60°C, and the vacuum degree is -0.09Mpa--0.10Mpa. The application does not particularly limit the sintering method, as long as the purpose of the application can be achieved. For example, a tubular furnace programmed heating method is used, first heated at 150-300°C for 2-4 hours, and then sintered at 500-600°C for 4-6 hours.

[0045] The second aspect of the application provides a full solid-state lithium battery, which comprises a positive electrode, a negative electrode and the sulfide solid-state electrolyte of the first aspect of the application.

[0046] The application does not particularly limit the positive electrode and the negative electrode in the full solid-state lithium battery, as long as the purpose of the application can be achieved. For example, the positive electrode comprises a positive electrode active material, a sulfide solid-state electrolyte and a conductive carbon, the positive electrode comprises a positive electrode active material, a sulfide solid-state electrolyte and a conductive carbon, and the positive electrode active material can be ternary positive electrode NCM523, NCM622, NCM712, NCM811, NCM90, or lithium iron phosphate, lithium manganese iron phosphate LiMn x Fe 1-x PO4, LiCoO2 material, lithium-rich manganese-based material (aLi2MnO3•(1-a)LiMO2) (0≤a≤1, M is at least one of Ni, Co or Mn), lithium nickel manganese oxide (LiNi 0.5 Mn 1.5 O4) material, etc., the sulfide solid-state electrolyte is the electrolyte in the application, and the conductive carbon can be Super P, carbon black; the mass ratio of the positive electrode active material, the sulfide solid-state electrolyte and the conductive carbon can be 60-80%:10-35%:3-10%. The negative electrode comprises lithium-indium alloy, lithium metal, graphite, silicon-carbon. Preferably, the full solid-state lithium battery further comprises a current collector arranged on the side of the positive electrode material; the current collector can be a carbon-coated aluminum foil or a pure aluminum foil.

[0047] The preparation method of the all-solid-state lithium battery is not particularly limited in the present application, and any method that can achieve the purpose of the present application can be used, for example, the preparation method of the all-solid-state lithium battery includes: mixing a positive electrode active material, a sulfide solid electrolyte and conductive carbon to obtain a composite positive electrode powder; the sulfide solid electrolyte is loaded into a solid-state battery mold for first pressing to obtain an electrolyte layer; the composite positive electrode powder is added to one side of the electrolyte layer for second pressing to obtain a positive electrode; and a negative electrode material is added to the other side of the electrolyte layer for third pressing to obtain an all-solid-state lithium battery.

[0048] The sulfide solid electrolyte of the present application has good structural stability, high ionic conductivity and good air stability, and thus the all-solid-state lithium battery comprising the sulfide solid electrolyte of the present application has excellent electrochemical performance.

[0049] Examples

[0050] Hereinafter, examples and comparative examples are given to more specifically describe the embodiments of the present application. Various tests and evaluations are performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0051] Test method and equipment:

[0052] Ionic conductivity test

[0053] In an argon-filled glove box, 100 mg of sulfide solid electrolyte powder was weighed and placed in a mold battery with a diameter of 9 mm stainless steel sheet at both ends (Wuhan Chuangneng CN-01), and was pressure-formed at a pressure of 200 MPa, with an electrolyte sheet thickness of 1 mm. The mold battery was used for AC impedance spectroscopy test.

[0054] In an argon-filled glove box, 110 mg of sulfide solid electrolyte powder was weighed and placed in a mold battery with a diameter of 9 mm stainless steel sheet at both ends (Wuhan Chuangneng CN-01), and was pressure-formed at a pressure of 300 MPa, with an electrolyte sheet thickness of 1 mm. The mold battery was used for AC impedance spectroscopy test.

[0055] AC impedance spectroscopy test: The electrolyte impedance was measured by electrochemical impedance spectroscopy (EIS) at 25°C, and the impedance was measured on an electrochemical workstation (ChenHua, CHI630E) by applying a direct current (DC) polarization voltage of 1V, with an amplitude of 50mV and a frequency range of 1Hz~10MHz. The ionic conductivity of the electrolyte material was calculated according to the following ionic conductivity formula, as follows:

[0056]

[0057] wherein σ is the ionic conductivity, with a unit of S cm –1L is the thickness of the electrolyte sheet in cm; R is the electrolyte resistance in S is the effective contact area of the stainless steel sheet and the electrolyte powder in cm 2 .

[0058] Air stability test

[0059] Air stability is mainly described by the retention rate of the ionic conductivity of the sulfide solid electrolyte under air exposure.

[0060] Ionic conductivity retention rate test: The ionic conductivity of the sulfide solid electrolyte is tested using the above-mentioned ionic conductivity test method, which is recorded as the conductivity before exposure; then the sulfide solid electrolyte is directly exposed to air at a dew point temperature of -40°C, and the sulfide solid electrolyte is recovered at 12 hours, 24 hours, and 48 hours, respectively, and the ionic conductivity is tested using the above-mentioned ionic conductivity test method, which is recorded as the conductivity after exposure. The conductivity retention rate = conductivity after exposure / conductivity before exposure x 100%.

[0061] X-ray powder diffraction test

[0062] X-ray powder diffraction (XRD) technology is used to analyze the crystal structure of the sample. The experiment uses a Bruker D8 Advance diffractometer equipped with Cu Kα radiation (λ = 1.5406 Å) as the light source. The test parameters are set as follows: tube voltage is 40 kV, tube current is 40 mA, scanning range is 2θ = 5°-90°, scanning step is 0.02°, and scanning rate is 5° / min. The sample is uniformly dispersed in the form of powder on a glass slide without diffraction background, and is treated by compaction to reduce the influence of inter-particle voids on the diffraction results.

[0063] Jade software is used to process and analyze the XRD data. First, the raw data is imported into the software, background subtraction and signal optimization are performed. The peak search function is used to automatically identify the diffraction peak position, and the Gaussian function is selected for peak shape fitting. The parameters are adjusted to make the fitted curve consistent with the experimental data. After fitting, the software directly outputs the peak area I of the diffraction peak.

[0064] Calculation of the ratio of impurity peaks to main peaks in XRD after 24 hours of exposure: The sulfide solid electrolyte is directly exposed to air at a dew point temperature of -40°C for 24 hours, and the sulfide solid electrolyte is recovered. The peak area of the impurity peaks and the main peaks is tested using the above method and the ratio of the two is calculated.

[0065] Cell parameter analysis: The XRD data were processed and analyzed by Jade software. First, the original data were imported into the software, and after background subtraction and signal optimization, they were exported as text format. The text file was imported into the refinement software FullProf, and an initial model was established according to the known crystal structure of the sample. The preliminary cell parameters and space group were input, and the instrument parameters such as zero point offset, sample displacement were adjusted, and the preliminary fitting was completed.

[0066] During the refinement process, the peak shape parameters (such as peak width, peak shape factor), background function, cell parameters (a, b, c, α, β, γ) and atomic position and occupancy were optimized step by step, and finally the convergence of fitting was realized. The evaluation of fitting results was based on the goodness of fit Chi2, and the fitting quality was judged by combining the residual spectrum. When the refinement result converges (Chi2<3), the cell parameters a, b, c can be obtained from the result text output by the software.

[0067] Test of particle size distribution

[0068] A Zeiss Sigma 300 scanning electron microscope (SEM) was used to observe the surface morphology and particle size distribution of the sulfide solid-state electrolyte. It was fixed on the sample stage, and the sample stage was placed in the vacuum chamber. The acceleration voltage, beam intensity and working distance of the SEM were adjusted to optimize the imaging effect, and the surface morphology information was obtained by the secondary electron detector. Image J software was used to measure and count the particle size of the sulfide solid-state electrolyte in the SEM image, and the particle size distribution was obtained.

[0069] Electrochemical performance test

[0070] The electrochemical performance test was mainly carried out by assembling full solid-state batteries with sulfide solid-state electrolyte and layered high-nickel NCM811 ternary positive electrode material.

[0071] Preparation of all-solid-state battery: (1) Preparation of positive electrode material: the positive active material NCM811, the sulfide solid electrolyte of the application and conductive carbon were mixed in a mass ratio of 75:20:5, ground in a mortar for 30 minutes to obtain a composite positive electrode powder; (2) Negative electrode material: lithium-indium alloy (lithium content of 30wt%); (3) Sulfide solid electrolyte: the sulfide solid electrolyte of the application was used; (4) Assembly of all-solid-state battery: in an argon-filled glove box, first, 100 mg of sulfide solid electrolyte was added to a solid-state battery mold with an inner diameter of 10 mm, and was pressed to 300 MPa for 1 minute to obtain an electrolyte layer; 10 mg of composite positive electrode powder was added to one side of the electrolyte layer, covered with a 15 µm aluminum foil, and pressed to 100 MPa for 1 minute to obtain a positive electrode; then 100 µm lithium-indium alloy negative electrode material was added to the other side, and after slight pressing at 50 MPa, the mold was assembled to obtain an assembled all-solid-state lithium ion battery, which was verified for airtightness and then taken out of the glove box and transferred to a battery test system for electrochemical charge and discharge cycle test.

[0072] Charge and discharge test: The charge and discharge performance test of the battery was carried out using a LAND battery test system at a constant temperature of 25℃.

[0073] Constant current charge and discharge test can directly reflect the electrochemical performance of active materials in the battery, and is an important means to evaluate the practical application potential of materials. In the test, the current density is based on the mass of the material, and the specific capacity corresponding to 1C is defined as , where 0.2C is . During the 0.2C rate cycle, first, the battery is charged from 2.6 V to a pre-set cut-off voltage (3.9 V, 4.0 V, 4.1 V, 4.2 V, 4.3 V or 4.4 V) at a constant current, and the highest voltage at which the battery can stably operate is selected as the cut-off voltage, then discharged to 2.6 V at the same current, and the whole process is completed in constant current mode. The capacity retention rate (initial efficiency) of the all-solid-state lithium ion battery in the first 0.2C charge and discharge process, the capacity retention rate after 200 cycles in the 0.2C charge and discharge cycle process, and the cycle number of the all-solid-state lithium ion battery when the discharge capacity jumps (the discharge capacity jump of the application refers to a sudden and sharp decrease in discharge capacity) are recorded.

[0074] The specific capacity of the first charge and discharge process of the battery is used to calculate the first discharge efficiency (initial efficiency), which is calculated as: initial efficiency = first discharge capacity / first charge capacity x 100%. This index can be used to evaluate the capacity loss caused by irreversible reactions (such as electrolyte decomposition or solid-state electrolyte interface film formation) in the first cycle.

[0075] Capacity retention rate after 200 cycles = 200th discharge capacity / first discharge capacity x 100%.

[0076] Example 1

[0077] In an Ar atmosphere, raw materials of Li2S, P2S5, LiCl, LiBr and rare earth oxide CeO2 with a molar ratio of 2.15:0.5:0.875:0.375:0.05 were weighed, 1 kg of the raw materials was added into 1 kg of n-hexane for mixing to obtain a suspension; the suspension was subjected to vacuum distillation drying under the condition of a temperature of 40°C and a vacuum degree of -0.098 Mpa to obtain a solid electrolyte precursor mixture; the solid electrolyte precursor mixture obtained above was heated at 200°C for 3 hours and then at 550°C for 5 hours in a tube furnace in an Ar atmosphere to obtain a sulfide solid electrolyte (Li 5.55 PCe 0.05 S 4.65 O 0.1 Cl 0.875 Br 0.375 ), and an X-ray diffraction pattern thereof is shown in FIG. 1. Figure 1

[0078] Examples 2 to 8

[0079] Except for adjusting the molar ratio of raw materials to obtain sulfide solid electrolytes of different chemical formulas in Table 1, the remaining steps were the same as in Example 1.

[0080] Example 9

[0081] The raw materials were replaced with “raw materials of Li2S, P2S5, LiCl, LiBr, P2O5, elemental S and rare earth oxide Eu2O3 with a molar ratio of 2.15:0.495:0.875:0.375:0.005:0.025:0.025”, and the remaining steps were the same as in Example 1 to obtain a sulfide solid electrolyte (Li 5.55 PEu 0.05 S 4.65 O 0.1 Cl 0.875 Br 0.375 ), and an X-ray diffraction pattern thereof is shown in FIG. 4. Figure 2

[0082] Example 10

[0083] The raw materials were replaced with “raw materials of Li2S, P2S5, LiCl, LiBr and rare earth oxide PrO2 with a molar ratio of 2.15:0.5:0.875:0.375:0.05”, and the remaining steps were the same as in Example 1 to obtain a sulfide solid electrolyte (Li 5.55 PPr 0.05 S 4.65 O 0.1 Cl 0.875 Br​​0.375 The remaining steps were the same as in Example 1 except that the starting materials were replaced with "starting materials of Li2S, P2S5, LiCl, LiBr, P2O5, S, and rare earth oxide Y2O3 in a molar ratio of 2.15:0.5:0.875:0.375:0.05." A sulfide solid-state electrolyte (Li Figure 3 PSY

[0084] Example 11

[0085] The starting materials were replaced with "starting materials of Li2S, P2S5, LiCl, LiBr, P2O5, S, and rare earth oxide Sm2O3 in a molar ratio of 2.15:0.495:0.875:0.375:0.005:0.025:0.025." A sulfide solid-state electrolyte (Li 5.55 PSm 0.05 S 4.65 O 0.1 Cl 0.875 Br 0.375 The remaining steps were the same as in Example 1 except that the starting materials were replaced with "starting materials of Li2S, P2S5, LiCl, LiBr, P2O5, S, and rare earth oxide Y2O3 in a molar ratio of 2.15:0.5:0.875:0.375:0.05." A sulfide solid-state electrolyte (Li Figure 4 PSY

[0086] Example 12

[0087] The starting materials were replaced with "starting materials of Li2S, P2S5, LiBr, LiI, and rare earth oxide CeO2 in a molar ratio of 2.15:0.5:0.875:0.375:0.05." A sulfide solid-state electrolyte (Li 5.55 PCe 0.05 S 4.65 O 0.1 Br 0.875 I 0.375 The remaining steps were the same as in Example 1 except that the starting materials were replaced with "starting materials of Li2S, P2S5, LiCl, LiI, and rare earth oxide Y2O3 in a molar ratio of 2.15:0.5:0.875:0.375:0.05." A sulfide solid-state electrolyte (Li PCe

[0088] Example 13

[0089] The starting materials were replaced with "starting materials of Li2S, P2S5, LiCl, LiI, and rare earth oxide CeO2 in a molar ratio of 2.15:0.5:0.875:0.375:0.05." A sulfide solid-state electrolyte (Li 5.55 PCe 0.05 S 4.65 O 0.1 Cl 0.875 I 0.375 The remaining steps were the same as in Example 1 except that the starting materials were replaced with "starting materials of Li2S, P2S5, LiCl, LiI, and rare earth oxide Y2O3 in a molar ratio of 2.15:0.5:0.875:0.375:0.05." A sulfide solid-state electrolyte (Li

[0090] PCe

[0091] The starting materials were replaced with "starting materials of Li2S, P2S5, LiCl, LiBr, LiI, and rare earth oxide CeO2 in a molar ratio of 2.15:0.5:0.875:0.25:0.125:0.05." A sulfide solid-state electrolyte (Li 5.55 PCe0.05 S 4.65 O 0.1 Cl 0.875 Br 0.25 I 0.125 ), the remaining steps are the same as those in Example 1.

[0092] Example 15

[0093] The raw materials were replaced with "Li2S, P2S5, LiCl and rare earth oxide CeO2 with a molar ratio of 2.15:0.5:1.25:0.05" to obtain a sulfide solid electrolyte (Li 5.55 PCe 0.05 S 4.65 O 0.1 Cl 1.25 ), the remaining steps are the same as those in Example 1.

[0094] Example 16

[0095] The raw materials were replaced with "Li2S, P2S5, LiCl, LiBr, rare earth oxide CeO2, P2O5, S element and rare earth oxide Eu2O3 with a molar ratio of 2.15:0.4975:0.875:0.375:0.025:0.0025:0.0125:0.0125" to obtain a sulfide solid electrolyte (Li 5.55 PCe 0.025 Eu 0.025 S 4.65 O 0.1 Cl 0.875 Br 0.375 ), the remaining steps are the same as those in Example 1.

[0096] Example 17

[0097] The raw materials were replaced with "Li2S, P2S5, LiCl, LiBr and rare earth oxide CeO2 with a molar ratio of 2.15:0.5:0.625:0.625:0.05" to obtain a sulfide solid electrolyte (Li 5.55 PCe 0.05 S 4.65 O 0.1 Cl 0.625 Br 0.625 ), the remaining steps are the same as those in Example 1.

[0098] Example 18

[0099] The sulfide solid electrolyte is the same as that in Example 1, and the positive electrode active material for the electrochemical performance test is Li 1.2 Ni 0.13 Co 0.13 Mn0.54 O2, the negative electrode material is graphite, and the remaining electrochemical performance test steps are the same as the above test method.

[0100] Example 19

[0101] The sulfide solid electrolyte is the same as that in Example 1, the positive electrode active material for electrochemical performance test is LiFe 0.5 Mn 0.5 PO4, the negative electrode material is silicon-carbon, and the remaining electrochemical performance test steps are the same as the above test method.

[0102] Comparative Examples 1 to 4

[0103] Except that the molar ratio of raw materials is adjusted to obtain sulfide solid electrolytes of different chemical formulas in Table 1, the remaining steps are the same as those in Example 1.

[0104] Comparative Example 5

[0105] The raw materials are replaced with "raw materials of Li2S, P2S5, LiCl and LiBr with a molar ratio of 2.25: 0.5: 0.875: 0.375", to obtain a sulfide solid electrolyte (Li 5.75 PS 4.75 Cl 0.875 Br 0.375 ) except that the remaining steps are the same as those in Example 1. Its X-ray diffraction pattern is shown in Figure 5 .

[0106] Comparative Example 6

[0107] The raw materials are replaced with "raw materials of Li2S, P2S5, LiCl, LiBr and CeS2 with a molar ratio of 2.25: 0.5: 0.875: 0.375: 0.05", to obtain a sulfide solid electrolyte (Li 5.75 PCe 0.05 S 4.75 Cl 0.875 Br 0.375 ) except that the remaining steps are the same as those in Example 1.

[0108] Comparative Example 7

[0109] Except that the molar ratio of raw materials is adjusted to obtain a sulfide solid electrolyte (Li 5.71 PCe 0.01 S 4.75 Cl 0.875 Br 0.375 ) except that the remaining steps are the same as those in Comparative Example 6.

[0110] Comparative Example 8

[0111] The raw materials were replaced with "raw materials of Li2S, P2S5, LiCl, LiBr, P2O5 in a molar ratio of 2.25:0.48:0.875:0.375:0.02", to obtain the sulfide solid electrolyte (Li 5.75 PS 4.65 O 0.1 Cl 0.875 Br 0.375 ), and the remaining steps were the same as in Example 1.

[0112] Comparative Example 9

[0113] Except for adjusting the molar ratio of the raw materials, to obtain the sulfide solid electrolyte (Li 5.75 PS 4.73 O 0.02 Cl 0.875 Br 0.375 ), the remaining steps were the same as in Comparative Example 8.

[0114] Comparative Example 10

[0115] Except for replacing the raw materials with "raw materials of Li2S, P2S5, LiCl, LiBr and ZnO in a molar ratio of 1.85:0.5:1.4:0.2:0.05", to obtain the sulfide solid electrolyte Li 5.3 Zn 0.05 PS 4.35 O 0.05 Cl 1.4 Br 0.2 , the remaining steps were the same as in Example 1.

[0116] The preparation parameters and performance parameters of the sulfide solid electrolytes of each example and comparative example are shown in Table 1, and the performance parameters of the all-solid-state batteries prepared therefrom are shown in Tables 2 and 3.

[0117] Table 1 Preparation parameters and performance parameters of sulfide solid electrolytes

[0118] In Table 1, " / " represents no relevant parameters.

[0119] Table 2 Performance parameters of all-solid-state batteries

[0120] Table 3 Performance parameters of all-solid-state batteries of different systems

[0121] As can be seen from Table 1, the cell parameters of the sulfide solid-state electrolyte of the present application satisfy a = b = c = 9.85~10Å; the particle size of the sulfide solid-state electrolyte satisfies 0.5µm < D50 < 4µm, 7µm < D90 < 10µm; the sulfide solid-state electrolyte has high ionic conductivity and good air stability, the ionic conductivity is >5 mS / cm, the conductivity retention rate is ≥85% after exposure at a dew point temperature of -40℃ for 12 hours, the conductivity retention rate is ≥79% after exposure at a dew point temperature of -40℃ for 24 hours, the conductivity retention rate is ≥70% after exposure at a dew point temperature of -40℃ for 48 hours, and the ratio of impurity peak to main peak is ≤0.17% after exposure at a dew point temperature of -40℃ for 24 hours. As can be seen from Table 2, the sulfide solid-state electrolyte of the present application applied in a full solid-state lithium battery can improve the first discharge efficiency, cycle performance and cut-off voltage of the full solid-state lithium battery, the first discharge efficiency is ≥80.5%, the capacity retention rate after 0.2C cycle for 200 times is ≥95.0%, the cycle number at 0.2C is ≥329 times, and the cut-off voltage is ≥4.2V. As can be seen from Table 3, the sulfide solid-state electrolyte of the present application applied in full solid-state lithium batteries of different systems, the obtained full solid-state lithium batteries have high first discharge efficiency, good cycle performance and high cut-off voltage. In summary, the sulfide solid-state electrolyte of the present application improves the structural stability of the sulfide electrolyte in a complex electrochemical environment, and also improves the air stability and ionic conductivity of the sulfide solid-state electrolyte, thereby improving the initial efficiency, cycle life of the full solid-state lithium battery and increasing the working voltage, i.e., the sulfide solid-state electrolyte of the present application applied in a full solid-state lithium battery can improve the electrochemical performance of the full solid-state lithium battery.

[0122] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the scope of protection of the present application.

Claims

1. A sulfide solid electrolyte with the chemical formula Li 7-4x-y PM x S 6-2x-y O 2x X y , M is at least one of the variable valence rare earth elements Ce, Eu, Pr and Sm, X is at least one of the halogens, 0.005≤x≤0.3, 0.5≤y≤2, and the molar ratio of the M element to the O element is 1:

2.

2. The sulfide solid electrolyte according to claim 1, wherein 0.02≤x≤0.15, 1.25≤y≤1.

75.

3. The sulfide solid electrolyte according to claim 1, wherein X is at least one of Cl, Br and I.

4. The sulfide solid electrolyte according to claim 1, wherein The chemical formula of the sulfide solid electrolyte is Li 7-4x-y PM x S 6-2x-y O 2x X' 0.7y X'' 0.3y , X' or X'' are each independently Cl, Br or I, and X' and X'' are different.

5. The sulfide solid electrolyte according to claim 1, wherein The chemical formula of the sulfide solid electrolyte is Li 7-4x-y PM x S 6-2x-y O 2x Cl 0.7y Br 0.3y .

6. The sulfide solid electrolyte according to claim 1, wherein The sulfide solid electrolyte is Li 5.55 PCe 0.05 S 4.65 O 0.1 Cl 0.875 Br 0.375 、Li 5.67 PCe 0.02 S 4.71 O 0.04 Cl 0.875 Br 0.375 、Li 5.05 PCe 0.05 S 4.15 O 0.1 Cl 1.225 Br 0.525 、Li 5.55 PEu 0.05 S 4.65 O 0.1 Cl 0.875 Br 0.375 、Li 5.55 PPr 0.05 S 4.65 O 0.1 Cl 0.875 Br 0.375 、Li 5.55 P S 0.0 5S 4.65 O 0.1 Cl 0.875 Br 0.375 .

7. The sulfide solid electrolyte according to claim 1, wherein The unit cell parameters of the sulfide solid electrolyte satisfy: a=b=c=9.85~10Å.

8. The sulfide solid electrolyte according to claim 1, wherein The particle size of the sulfide solid electrolyte satisfies: 0.5µm<D50<4µm, 7µm<D90<10µm.

9. The sulfide solid electrolyte according to claim 1, wherein The ionic conductivity of the sulfide solid electrolyte is greater than 5 mS / cm.

10. An all-solid-state lithium battery comprising a positive electrode, a negative electrode, and the sulfide solid electrolyte according to any one of claims 1 to 9.

Images