A composite cathode for solid-state lithium-sulfur batteries and a method of making the same

Abstract

The application relates to a composite positive electrode for a solid-state lithium-sulfur battery and a preparation method thereof, and belongs to the field of all-solid-state lithium-sulfur batteries. By introducing an additive rare earth perovskite oxide (LaNiO3, LaCoO3, LaFeO3) into the solid-state lithium-sulfur battery positive electrode, the additive of the application has electronic conductivity, lithium ion conductivity and catalytic activity, accelerates the solid-phase bidirectional conversion of S8-Li2S, and reduces the interface charge transfer energy barrier. Test results show that the composite positive electrode has high specific capacity and cycle stability under high sulfur loading conditions, the discharge capacity at a 0.5C rate is more than 1200 mAh.g ‑1 After 500 cycles, the capacity retention rate is not less than 95%. The method has simple process and can be suitable for various solid-state battery systems, and has important significance for the practicalization of the solid-state lithium-sulfur battery.

Description

TECHNICAL FIELD

[0001] The present application relates to a composite positive electrode for solid-state lithium-sulfur batteries and a preparation method thereof, and belongs to the field of all-solid-state lithium-sulfur batteries. BACKGROUND

[0002] Lithium-sulfur batteries are considered as an important candidate system for the next generation of high specific energy secondary batteries due to the high theoretical specific capacity of 1675 mAh·g -1 and the specific energy density of 2600 Wh·kg -1 . All-solid-state lithium-sulfur batteries (ASSLSBs) replace liquid organic electrolyte with inorganic solid-state electrolyte, which not only avoids the safety risk of flammable solvents, but also effectively suppresses the shuttle effect of polysulfides, reduces parasitic side reactions, self-discharge and active material loss, thereby having high energy density and safety.

[0003] Unlike the liquid system, the sulfur redox process of ASSLSBs is no longer through soluble polysulfide intermediates, but is completely limited to solid-solid conversion; the reaction of S→Li2S must rely on the simultaneous transmission of Li + and electrons in the limited permeable network, and the reaction area is limited to a narrow three-phase boundary. Under the conditions of thick electrodes and high sulfur loading, insufficient ion flux, uninterrupted electronic skeleton or excessive pore tortuosity will all lead to limited sulfur participation in the reaction and form "dead sulfur", thereby reducing the capacity utilization and rate capability.

[0004] The performance of ASSLSBs is constrained by both transport and kinetics: on the one hand, poor contact and interface side reactions between solid-state electrolytes (such as sulfide-based Li6PS5Cl, oxide-based LLZO, etc.) and sulfur / conductive phases can lead to an increase in interfacial charge transfer impedance; on the other hand, the intrinsic kinetics of Li2S nucleation / decomposition is slow, which makes the polarization rapidly amplified at medium and high rates. In actual tests, the overpotential is mainly dominated by the interfacial charge transfer, followed by concentration polarization and ohmic polarization, which reflects the necessity of accelerating the solid-phase sulfur reduction.

[0005] Existing improvement strategies mostly introduce catalysts or conductive additives to improve electron / ion conduction and promote sulfur species conversion, such as transition metal compounds, carbon materials, MXene, etc., as in patent documents CN117855392A, CN118825232A, CN119029141B. Although these solutions improve the interface or conductive network to some extent, they generally use independent particle phase dispersion, which can dilute the effective reaction interface and disrupt the permeability continuity; under the conditions of thick electrodes and high sulfur loading, the catalytic gain is significantly attenuated with the diffusion distance and discontinuous channels, making it difficult to balance high specific energy and long cycle.

[0006] In addition, the composite cathode may also face the following problems during preparation and service: ion channel blockage caused by compaction densification, microcracks and contact degradation caused by chemical / mechanical incompatibility between the binder / electrolyte and sulfur or the conductive phase, and the cumulative effect of volume change in the electrode during long-term cycling. These factors further exacerbate the interface impedance and solid-phase conversion delay.

[0007] In summary, there is an urgent need for a new type of efficient additive with electronic conductivity, lithium ion conductivity and catalytic activity for the solid-state lithium-sulfur battery cathode, which can build a continuous electron-ion-reaction channel inside the composite electrode, taking into account high sulfur loading, low impedance and long cycle stability, and adapting to existing sulfide / oxide solid-state electrolyte systems. SUMMARY

[0008] In view of the deficiencies of the prior art, the present application provides a composite cathode for a solid-state lithium-sulfur battery and a preparation method thereof.

[0009] One of the technical problems to be solved by the present application is that in a solid-state lithium-sulfur battery, the solid-solid conversion kinetics of the sulfur cathode is slow, the interface charge transfer impedance is high, and the ion and electron transport paths are insufficient, resulting in low active sulfur utilization, poor rate performance, and insufficient cycle stability.

[0010] The second technical problem to be solved by the present application is that existing additives only have electronic conductivity or catalytic function, but lack effective lithium ion conductivity, cannot build a continuous electron-ion-reaction three-channel, and are difficult to meet the practical application requirements of high loading and long cycle.

[0011] The present application effectively solves the problems of discontinuous electron and lithium ion conduction path, high interface charge transfer impedance, and slow solid-solid conversion kinetics in existing composite cathodes by introducing rare earth perovskite oxides (LaNiO3, LaCoO3, LaFeO3) into the solid-state lithium-sulfur battery cathode.

[0012] The present application achieves the object of the present application by the following technical solutions:

[0013] A composite cathode for a solid-state lithium-sulfur battery, the composite cathode comprising: a sulfur-loaded composite S@C, a solid-state electrolyte, and a cathode additive, the cathode additive being a perovskite-type rare earth oxide with a general formula of LaBO3, wherein B is selected from one or more than two mixtures of Ni, Co, and Fe.

[0014] According to the present application, the perovskite-type rare earth oxide is specifically selected from one of the following:

[0015] LaNiO3 (LNO), LaCoO3 (LCO), and LaFeO3 (LFO).

[0016] According to the application, preferably, the additive amount of the composite positive electrode perovskite-type rare earth oxide is 3-15% of the total mass of the positive electrode.

[0017] According to the application, preferably, the perovskite-type rare earth oxide is prepared by the following method:

[0018] (1) mixing and stirring the transition metal salt solution and the rare earth salt solution for 10-60 min to obtain a mixed solution;

[0019] (2) slowly adding an aqueous precipitant solution into the mixed solution and stirring for 3-8 h to generate a precipitate;

[0020] (3) filtering the obtained precipitate and repeatedly washing with deionized water until the filtrate is close to neutral to obtain a wet precipitate;

[0021] (4) drying the wet precipitate to obtain a precursor powder;

[0022] (5) uniformly grinding the precursor powder and calcining at 600-800℃ under air atmosphere for 3-8 h to obtain the perovskite-type rare earth oxide.

[0023] According to the application, preferably, in step (1), the concentration of the transition metal salt solution is 0.05-1 mol·L -1 , and the transition metal salt is nickel nitrate hexahydrate, cobalt nitrate hexahydrate or iron nitrate nine hydrate.

[0024] According to the application, preferably, in step (1), the concentration of the rare earth salt solution is 0.05-1 mol·L -1 , and the rare earth salt is lanthanum nitrate hexahydrate.

[0025] According to the application, preferably, in step (1), the molar ratio of the transition metal salt in the transition metal salt solution to the rare earth salt in the rare earth salt solution is (1-2):(1-2).

[0026] According to the application, preferably, in step (2), the concentration of the aqueous precipitant solution is 0.02-0.2 g / mL, the precipitant is sodium carbonate, sodium hydroxide or potassium hydroxide, and the aqueous precipitant solution is added into the mixed solution until complete precipitation.

[0027] According to the application, preferably, in step (2), the molar ratio of the precipitant in the aqueous precipitant solution to the metal ions in the mixed solution is 2-4:1.

[0028] According to the application, preferably, in step (4), the drying is performed at 80-120℃ for 8-15 h.

[0029] According to the application, preferably, in step (5), the calcination temperature is 700℃ and the calcination time is 5 h.

[0030] The rare earth perovskite oxide of the application has mixed ionic-electronic conductor (MIEC) characteristics, can provide certain lithium ion conduction capacity while maintaining high electronic conductivity, and catalyzes the S8 ↔ Li2S conversion process through oxygen vacancies and its surface active sites.

[0031] According to the application, preferably, the sulfur-loaded composite S@C is selected from S@Ketjen Black, S@CNT, S@BP2000 or S@SuperP.

[0032] The S@Ketjen Black, S@CNT, S@BP2000 or S@SuperP are prepared according to the prior art.

[0033] According to the application, preferably, the solid-state electrolyte is Li6PS5Cl, Li 10 GeP2S 12 or Li3PS4.

[0034] The preparation method of the composite cathode for the solid-state lithium-sulfur battery comprises the following steps:

[0035] 1) Mix elemental sulfur and a conductive agent in a mass ratio of sulfur: conductive agent = 7:3, seal in an inert atmosphere, heat at 150-160 ℃ for 10-15 h, so that sulfur penetrates into the pores of carbon black; then heat to 210-230 ℃ for 3-5 h to obtain a sulfur-loaded composite S@C;

[0036] 2) Mix the sulfur-loaded composite S@C, the solid-state electrolyte and the perovskite rare earth oxide in a mass ratio of (30-50):(30-50):(1-10) to obtain a mixed powder;

[0037] 3) Ball mill the mixed powder to obtain a uniform cathode composite powder.

[0038] According to the application, preferably, in step 1), the conductive agent is selected from Ketjen Black or Super p, and the inert atmosphere is argon.

[0039] According to the application, preferably, in step 3), the ball milling speed is 200-600 rpm, and the time is 6-24 h.

[0040] The application has the following technical features and advantages:

[0041] By introducing rare earth perovskite oxides (LaNiO3, LaCoO3, LaFeO3) into the positive electrode of a solid-state lithium-sulfur battery, the problems of discontinuous electron and lithium ion conduction paths, high interface charge transfer impedance, and slow solid-solid conversion kinetics in the existing composite positive electrode are effectively solved. First, the rare earth perovskite itself has both electronic conductivity and certain lithium ion conductivity, which can form a continuous electron-ion-reaction three-channel inside the electrode, thereby improving the utilization rate of sulfur active material; second, the oxygen vacancies on the surface of the perovskite and the transition metal B-site active centers can catalyze the solid-phase bidirectional conversion process of S8-Li2S, reduce the interface impedance, and improve the rate performance; third, the rare earth perovskite can be uniformly mixed with the sulfur-carbon composite and the solid-state electrolyte, ensuring the structural stability of the composite positive electrode. Through the above synergistic effect, the composite positive electrode shows a specific capacity increase of 15-30% under high sulfur loading conditions, a capacity retention rate of not less than 95% after 500 cycles, and a discharge capacity of more than 1000 mAh·g -1 at 0.2-2 C rate, which is significantly better than the comparative example without adding rare earth perovskite. BRIEF DESCRIPTION OF DRAWINGS

[0042] Figure 1 X-ray diffraction pattern of LaNiO3 prepared in Example 1.

[0043] Figure 2 X-ray diffraction pattern of LaCoO3 prepared in Example 2.

[0044] Figure 3 X-ray diffraction pattern of LaFeO3 prepared in Example 3.

[0045] Figure 4 Transmission electron microscope image of LaNiO3 prepared in Example 1.

[0046] Figure 5 Transmission electron microscope image of LaCoO3 prepared in Example 2.

[0047] Figure 6 Transmission electron microscope image of LaFeO3 prepared in Example 3.

[0048] Figure 7 Charge-discharge measurement result graph of a full solid-state lithium-sulfur battery made of a composite sulfur positive electrode doped with 10% LaNiO3 of Experimental Example 1.

[0049] Figure 8 Charge-discharge measurement result graph of a full solid-state lithium-sulfur battery made of a composite sulfur positive electrode doped with 10% SuperP of the comparative sample of Experimental Example 1.

[0050] Figure 9A rate measurement result graph of a full solid-state lithium-sulfur battery made of the 10% LaNiO3-doped composite sulfur positive electrode of Experimental Example 2.

[0051] Figure 10 A rate measurement result graph of a full solid-state lithium-sulfur battery made of the 10% SuperP-doped composite sulfur positive electrode of Experimental Example 2. DETAILED DESCRIPTION

[0052] The application will be described in detail below with specific examples. The following examples are only for the convenience of those skilled in the art to understand the technical solutions of the application, implement or use the application, and do not limit the protection scope of the application.

[0053] In the examples, S@C and Li6PS5Cl are commercially available products. Example 1

[0054] Preparation of LaNiO3 additive

[0055] (1) 4.33 g of lanthanum nitrate hexahydrate (La(NO3)3·6H2O, 10 mmol) was weighed and dissolved in 50 mL of deionized water to obtain solution A;

[0056] (2) 2.91 g of nickel nitrate hexahydrate (Ni(NO3)2·6H2O, 10 mmol) was weighed and dissolved in 50 mL of deionized water to obtain solution B;

[0057] (3) Solution A and solution B were mixed and stirred for 30 min to obtain a mixed solution;

[0058] (4) 4.14 g of potassium carbonate (K2CO3, 30 mmol) was weighed and dissolved in 50 mL of deionized water to obtain solution C.

[0059] (5) Under stirring, solution C was slowly added to the mixed solution, and stirring was continued for 6 h to obtain a precipitate.

[0060] (6) The precipitate was filtered, washed with deionized water, dried at 100°C for 12 h, ground, and calcined at 700°C in air for 5 h to obtain the LaNiO3 additive.

[0061] The X-ray diffraction pattern of the LaNiO3 additive prepared in this example is shown in Figure 1 , and the transmission electron microscope is shown in Figure 4 X-ray powder diffraction (XRD) shows that the diffraction peaks of the sample are consistent with the standard card PDF#97-006-7716, and no obvious impurity phase peak is observed, indicating that the pure phase perovskite LaNiO3 is successfully prepared.

[0062] Transmission electron microscopy observed that the sample was nanoparticles, the average particle size of about 100 nm. Example 2

[0063] Preparation of LaCoO3additive

[0064] (1) 4.33 g of lanthanum nitrate hexahydrate (10 mmol) was weighed and dissolved in 50 mL of deionized water to obtain solution A.

[0065] (2) 2.91 g of cobalt nitrate hexahydrate (Co(NO3)2·6H2O, 10 mmol) was weighed and dissolved in 50 mL of deionized water to obtain solution B.

[0066] (3) Solution A and solution B were mixed and stirred for 30 min to obtain a mixed solution;

[0067] (4) 4.14 g of potassium carbonate (30 mmol) was weighed and dissolved in 50 mL of deionized water to obtain solution C;

[0068] (5) Solution C was slowly added to the mixed solution, and stirred for 6 h. The obtained precipitate was washed, dried at 100°C for 12 h, ground, and calcined at 700°C for 5 h to obtain LaCoO3powder.

[0069] The X-ray diffraction pattern of the LaCoO3additive prepared in this example is shown in Figure 2 , and the transmission electron microscopy is shown in Figure 5 . X-ray powder diffraction (XRD) showed that the diffraction peaks of the sample were consistent with the standard card PDF#97-009-9369, and no obvious impurity phase peak was observed, indicating that pure phase perovskite LaCoO3was successfully prepared.

[0070] Transmission electron microscopy observed that the sample was nanoparticles, the average particle size of about 100 nm. Example 3

[0071] Preparation of LaFeO3additive

[0072] (1) 4.33 g of lanthanum nitrate hexahydrate (10 mmol) was weighed and dissolved in 50 mL of deionized water to obtain solution A.

[0073] (2) 4.04 g of iron nitrate nonahydrate (Fe(NO3)3·9H2O, 10 mmol) was weighed and dissolved in 50 mL of deionized water to obtain solution B.

[0074] (3) Solution A and solution B were mixed and stirred for 30 min to obtain a mixed solution;

[0075] (4) 4.14 g of potassium carbonate (30 mmol) was weighed into 50 mL of deionized water to obtain solution C.

[0076] (5) Solution C was slowly added into the mixture under stirring, and stirring was continued for 6 h to obtain a precipitate.

[0077] (6) The obtained precipitate was washed, dried at 100°C for 12 h, ground, and calcined at 600°C for 5 h to obtain LaFe03 powder.

[0078] The X-ray diffraction pattern of the LaFe03 additive prepared in this example is shown in Figure 3 , and the transmission electron microscope is shown in Figure 6 . X-ray powder diffraction (XRD) showed that the diffraction peaks of the sample were consistent with the standard card PDF #97-002-8255, and no obvious impurity phase peak was observed, indicating that pure phase perovskite LaFe03 was successfully prepared.

[0079] Transmission electron microscope observation showed that the sample was a nanoparticle with an average particle size of about 100 nm. Example 4

[0080] Preparation of sulfur-carbon composite S@C

[0081] (1) 0.70 g of elemental sulfur and 0.30 g of Ketjen Black were weighed into a quartz tube and sealed under an argon atmosphere;

[0082] (2) Heating at 155°C for 12 h, and then heating at 220°C for 4 h to obtain a sulfur-loaded composite S@Ketjen Black. Example 5

[0083] Preparation of positive electrode composite

[0084] In a glove box, 0.40 g of the sulfur-loaded composite S@Ketjen Black prepared in Example 4, 0.50 g of solid-state electrolyte Li6PS5Cl, and 0.10 g of the LaNi03 powder prepared in Example 1 were weighed.

[0085] The above components were added into a sealed ball mill tank, and ball milling was carried out at 500 rpm for 12 h to obtain a uniformly mixed positive electrode composite powder. The powder was tabletted according to the existing method to obtain an electrode sheet. Comparative Example 1

[0086] Preparation of positive electrode composite (without adding rare earth perovskite additive)

[0087] In a glove box, 0.40 g of the sulfur-loaded composite S@Ketjen Black prepared in Example 4, 0.50 g of the solid electrolyte Li6PS5Cl and 0.10 g of Super P were weighed, and ball-milling and tabletting were performed under the same conditions as in Example 5 to obtain a comparative electrode plate.

[0088] Experimental Example 1: Cycle performance test

[0089] The composite cathode prepared in Example 5 was assembled into a full solid-state lithium-sulfur battery together with a metal indium / lithium alloy anode and a solid electrolyte Li6PS5Cl, and the composite cathode of Comparative Example 1 was assembled into a full solid-state lithium-sulfur battery together with a metal indium / lithium alloy anode and a solid electrolyte Li6PS5Cl to set up a control group.

[0090] The battery was subjected to constant current charge-discharge cycling at 25°C in a voltage range of 0.5-2.4 V at a current density of 0.5 C (1 C = 1675 mA·g -1 Sulfur calculation).

[0091] The test results of different batteries are shown in Figure 7 , 8 The test results show that, as shown in Figure 7 , the specific capacity of the full solid-state lithium-sulfur battery assembled with the cathode composite of the application is about 1117 mAh·g -1 in the first discharge, and the capacity retention rate is about 98% after 500 cycles. Compared with Comparative Example 1, Figure 8 , the capacity retention rate is increased by about 45%.

[0092] Experimental Example 2: Rate performance test

[0093] The composite cathode prepared in Example 5 was assembled into a full solid-state lithium-sulfur battery together with a metal indium / lithium alloy anode and a solid electrolyte Li6PS5Cl, and the composite cathode of Comparative Example 1 was assembled into a full solid-state lithium-sulfur battery together with a metal indium / lithium alloy anode and a solid electrolyte Li6PS5Cl to set up a control group; the rate performance was tested at 25°C.

[0094] The battery was discharged at different rates of 0.2 C, 0.4 C, 0.6 C, 0.8 C, 1.0 C, 1.5 C and 2.0 C in a voltage range of 0.5-2.4 V.

[0095] The test results of different batteries are shown in Figure 9 , 10 The test results show that the discharge specific capacity is about 1250 mAh·g⁻¹ at 0.2 C, 1145 mAh·g -1 at 1 C, and 1041 mAh·g -1When the rate is restored to 0.2C, the capacity is almost completely restored, indicating that the battery has good rate reversibility.

[0096] The anode composite prepared in Example 5 and the anode composite prepared in Comparative Example 1 were subjected to electrochemical performance test, and the results showed that the composite anode of Example 5 exhibited higher initial specific discharge capacity and more excellent cycle retention rate under the condition of 0.5C. It can be seen that the introduction of rare earth perovskite additive can effectively improve the reaction kinetics of the solid-state lithium-sulfur battery anode, reduce the interface impedance, and thus improve the specific capacity and cycle stability of the battery.

[0097] In summary, by introducing rare earth perovskite oxide into the sulfur-carbon composite-solid-state electrolyte system, a continuous electron-ion-reaction channel is established, and the problems of solid-solid conversion kinetics limitation and high interface impedance are solved. The method is simple and has strong applicability, and the obtained composite anode has high specific capacity and long cycle stability, which provides a new technical approach for the practical application of solid-state lithium-sulfur batteries.

Claims

1. A composite cathode for solid-state lithium-sulfur batteries, the composite cathode comprising: The composition includes a sulfur-loaded composite S@C, a solid electrolyte, and a positive electrode additive, wherein the positive electrode additive is a perovskite-type rare earth oxide. Perovskite-type rare earth oxides are specifically selected from one of the following: The addition amount of LaNiO3, LaCoO3, and LaFeO3, composite cathode perovskite rare earth oxides, is 3-15% of the total cathode mass. The sulfur-loaded complex S@C is selected from S@KetjenBlack, S@CNT, S@BP2000, or S@SuperP, and the solid electrolyte is Li6PS5Cl or Li10GeP2S. 12 Or Li3PS4; Perovskite-type rare earth oxides are prepared by the following method: (1) Mix the transition metal salt solution and the rare earth salt solution and stir for 10-60 min to obtain a mixed solution; (2) Slowly add the aqueous solution of the precipitant to the mixture and stir for 3-8 hours to generate a precipitate; (3) The obtained precipitate was filtered and washed repeatedly with deionized water until the filtrate was nearly neutral to obtain a wet precipitate; (4) Dry the wet precipitate to obtain the precursor powder; (5) After grinding the precursor powder evenly, calcine it at 600-800℃ for 3-8 hours in air atmosphere to obtain perovskite-type rare earth oxides.

2. The composite positive electrode according to claim 1, characterized in that, Step (1): The concentration of the transition metal salt solution is 0.05 to 1 mol·L-1, and the transition metal salt is nickel nitrate hexahydrate, cobalt nitrate hexahydrate, or iron nitrate nonahydrate.

3. The composite positive electrode according to claim 1, characterized in that, Step (1): The concentration of the rare earth salt solution is 0.05-1 mol·L-1. The rare earth salt is lanthanum nitrate hexahydrate. The molar ratio of the transition metal salt in the transition metal salt solution to the rare earth salt in the rare earth salt solution is (1-2):(1-2).

4. The composite positive electrode according to claim 1, characterized in that, Step (2): The concentration of the precipitant aqueous solution is 0.02-0.2 g / mL. The precipitant is sodium carbonate, sodium hydroxide or potassium hydroxide. The precipitant aqueous solution is added to the mixture until complete precipitation. The molar ratio of the precipitant to the metal ions in the mixture is 2-4:

1.

5. The composite positive electrode according to claim 1, characterized in that, In step (4), the drying is carried out at 80-120℃ for 8-15 hours. In step (5), the calcination temperature is 700℃ and the calcination time is 5 hours.

6. The method for preparing the composite cathode for solid-state lithium-sulfur batteries according to claim 1, comprising the following steps: 1) Mix elemental sulfur and conductive agent at a mass ratio of sulfur:conductive agent = 7:3, seal in an inert atmosphere, and heat at 150-160℃ for 10-15h to allow sulfur to penetrate into the pores of carbon black; then raise the temperature to 210-230℃ and hold for 3-5h to obtain sulfur-loaded composite S@C. 2) The sulfur-loaded composite S@C, the solid electrolyte, and the perovskite-type rare earth oxides are mixed in a mass ratio of (30-50):(30-50):(1-10) to obtain a mixed powder; 3) The mixed powder is ball-milled to obtain a uniform positive electrode composite powder.

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