A full-solid-state sulfide battery complementary strain NCM811 / LCO composite positive electrode and a preparation method thereof

Abstract

This invention relates to the field of all-solid-state sulfide battery technology, specifically to an all-solid-state sulfide battery complementary strain NCM811 / LCO composite cathode and its preparation method. The active material of the composite cathode includes high-nickel ternary cathode material NCM811 and lithium cobalt oxide (LCO), which are mixed by ball milling to form the composite cathode active material. Complementary strain is achieved by utilizing opposite mechanical deformation laws. The all-solid-state sulfide battery complementary strain NCM811 / LCO composite cathode of this invention utilizes the opposite mechanical deformation laws of NCM811 and LCO during charge and discharge to achieve complementary strain, reducing the overall deformation amplitude of the composite cathode, suppressing particle cracking and interface debonding, slowing impedance growth, and significantly improving cycle stability and rate performance. Preparation only requires ball milling mixing, without complex coating, making the process simple, low-cost, and suitable for mass production.

Description

Technical Field

[0001] This invention relates to the field of all-solid-state sulfide battery technology, specifically to an all-solid-state sulfide battery complementary strain NCM811 / LCO composite cathode and its preparation method. Background Technology

[0002] All-solid-state sulfide batteries are considered an important direction for the development of next-generation rechargeable batteries due to their advantages such as high safety and high energy density. However, unlike liquid electrolyte systems, the electrode and electrolyte in an all-solid-state system have a solid-solid contact and lack self-wetting and self-healing capabilities. Therefore, the volumetric stress changes in the electrode material during charging and discharging have a significant impact on battery performance.

[0003] High-nickel ternary cathode material NCM811 possesses high discharge specific capacity and high energy density, making it an important candidate material for achieving high energy density in all-solid-state sulfide batteries. However, NCM811 exhibits significant asymmetric mechanical deformation during charge and discharge: it contracts during charging and expands during discharging. This leads to stress concentration within the composite cathode, causing particle cracking, interface debonding, increased interfacial porosity, disruption of ion / electron transport channels, and a continuous increase in interfacial impedance, ultimately resulting in capacity decay and a decrease in rate performance.

[0004] While existing technologies employ methods such as coating, doping, and structural design to mitigate volume changes, most of these processes are complex, costly, and fail to fundamentally address the asymmetric deformation problem of NCM811. Therefore, there is an urgent need for a composite cathode with a simple structure that is easy to scale up for application. Summary of the Invention

[0005] To address the problems of the existing technologies, this invention provides a complementary strain NCM811 / LCO composite cathode for all-solid-state sulfide batteries and its preparation method. The method utilizes the opposite mechanical deformation laws of NCM811 and LCO during charge and discharge to achieve complementary strain, reducing the overall deformation amplitude of the composite cathode, suppressing particle cracking and interface debonding, mitigating impedance growth, and significantly improving cycle stability and rate performance. The preparation only requires ball milling and mixing, without complex coating, making the process simple, low-cost, and suitable for large-scale production.

[0006] The technical solution of the present invention to solve the above problems is as follows: A complementary strain NCM811 / LCO composite cathode for all-solid-state sulfide batteries is disclosed. The active material of the composite cathode includes high-nickel ternary cathode material NCM811 and lithium cobalt oxide (LCO). During charging and discharging, NCM811 exhibits contraction during charging and expansion during discharging. During charging and discharging, LCO exhibits expansion during charging and contraction during discharging. The two are mixed by ball milling to form the composite cathode active material, achieving complementary strain by utilizing opposite mechanical deformation laws.

[0007] Preferably, the mass ratio of the high-nickel ternary cathode material NCM811 to lithium cobalt oxide LCO is 50-80:20-50.

[0008] Preferably, the composite positive electrode further includes a sulfide solid electrolyte and a conductive agent, and the mass ratio of the composite positive electrode active material to the sulfide solid electrolyte and the conductive agent is 5.5-6.5:3.8-4.2:0.08-0.12.

[0009] Preferably, the sulfide solid electrolyte is Li6PS5Cl.

[0010] Preferably, the conductive agent is selected from at least one of conductive carbon black Super P, acetylene black, and carbon nanotubes.

[0011] The above-mentioned method for preparing the complementary strain NCM811 / LCO composite cathode for all-solid-state sulfide batteries includes the following steps: (1) Mix NCM811 powder and LCO powder in a mass ratio and ball mill at 150-350 rpm for 1-5 hours to obtain composite positive electrode active material; (2) The composite positive electrode active material is mixed with sulfide solid electrolyte and conductive agent to obtain composite positive electrode powder; (3) The composite cathode powder is cold-pressed to obtain the composite cathode layer.

[0012] Preferably, in step (1), the milling medium is zirconia balls, the ball-to-material mass ratio is 5-15:1, the milling time is 2-4 hours, and the milling speed is 200-300 rpm.

[0013] Preferably, the cold pressing pressure in step (3) is 300 MPa.

[0014] The present invention has the following beneficial effects: In the all-solid-state sulfide battery complementary strain NCM811 / LCO composite cathode of this invention, the high-nickel ternary cathode material NCM811 and lithium cobalt oxide (LCO) both belong to the layered oxide structure, but their cell parameter changes during charge and discharge processes show opposite trends. During the lithium stripping process of NCM811 during charging, due to the Ni... 3+ / Ni 4+ The ionic radius changes and the electrostatic repulsion between oxygen layers weakens, resulting in significant contraction along the c-axis; however, during lithium insertion in discharge, the c-axis expands. Conversely, during lithium extraction in LCO, Co... 3+ Oxidized to Co 4+ Although the ionic radius decreases, due to Li +After desorption, the enhanced electrostatic repulsion between oxygen layers and the changes in electronic structure result in overall cell expansion; during lithium intercalation during discharge, this manifests as contraction. When the two are combined in a certain ratio, at the electrode scale, the contraction / expansion of NCM811 and the expansion / contraction of LCO form a mechanical complementarity, significantly reducing the overall thickness variation and stress fluctuations of the composite cathode. This strain cancellation effect brings the following beneficial effects: (1) Reduce the concentration of shear stress and tensile stress between particles and at the particle / electrolyte interface, thereby reducing particle cracking and pulverization. (2) Maintain the effective contact area of ​​the solid-solid interface, suppress the generation of interface pores, and slow down the growth of interface impedance. (3) Reduce dependence on high stacking pressure and improve the cycle stability and rate performance of the battery; (4) By adjusting the LCO addition ratio, an adjustable range can be provided for different sulfide electrolyte systems and different stacking pressure conditions.

[0015] Compared with the prior art, the all-solid-state sulfide battery complementary strain NCM811 / LCO composite cathode of the present invention also has the following beneficial effects: (1) Solving the interface failure problem from the source: Unlike traditional passive protection strategies such as interface coating and surface modification, this invention reduces the overall deformation of the positive electrode during cycling from the source through complementary strain design, and actively prevents interface failure. (2) Significantly improved cycle stability: Examples show that after 50 cycles at 0.5C, the composite cathode with NCM811:LCO=6:4 exhibits significantly better particle integrity than pure NCM811, and the interface contact remains good. (3) Optimized impedance characteristics: DRT analysis shows that the charge transfer impedance fluctuation of the composite cathode during the charging process is significantly reduced and the interface stability is greatly improved; (4) Balancing capacity and efficiency: By optimizing the ratio, the first-cycle coulombic efficiency is significantly improved while maintaining a high discharge specific capacity; (5) The preparation method of the present invention is simple and low in cost: the complementary effect can be achieved by ball milling and mixing alone, without the need for complex coating process or high-cost nanostructure design, and has good prospects for industrial promotion. Attached Figure Description

[0016] Figure 1 The graph shows a comparison of the discharge specific capacity and coulombic efficiency of Examples 1-4 and Comparative Examples 1-2 in the first charge-discharge cycle of an all-solid-state sulfide battery. Figure 2 This is a comparison chart of the rate performance of Examples 1-4 and Comparative Examples 1-2 in all-solid-state sulfide batteries; Figure 3This is a comparison chart of the long-cycle performance of Examples 1-4 and Comparative Examples 1-2 in all-solid-state sulfide batteries; Figure 4 Comparison of FIB cross-section scanning electron microscope images of the positive electrode of Comparative Example 1 and Example 3 after 50 cycles of an all-solid-state sulfide battery; Figure 5 This is a comparison of the DRT (relaxation time distribution) spectra of Example 1 and Example 3 during the first charge-discharge cycle of an all-solid-state sulfide battery. Detailed Implementation

[0017] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0018] Example 1: Complementary strain composite cathode: A complementary strain NCM811 / LCO composite cathode for all-solid-state sulfide batteries is prepared as follows: (1) Weigh 8.0 g of NCM811 powder and 2.0 g of LCO powder, place them in a zirconia ball mill jar, add zirconia grinding balls (ball-to-material mass ratio 10:1), and ball mill and mix them at 250 rpm for 3 h under argon atmosphere protection to obtain composite cathode powder; (2) Place 6.0 g of the NL-8:2 composite cathode powder obtained in step (1), 3.9 g of Li6PS5Cl sulfide solid electrolyte, and 0.1 g of conductive carbon black Super P in a mortar and grind manually for 30 min until uniformly mixed to obtain composite cathode powder; (3) Weigh 80 mg of the composite cathode powder obtained in step (2), place it in a stainless steel mold with a diameter of 10 mm, and cold press it under a pressure of 300 MPa to obtain a composite cathode layer with a thickness of about 150 μm.

[0019] Example 2: A complementary strain NCM811 / LCO composite cathode for all-solid-state sulfide batteries differs from Example 1 in that: in step (1), the mass ratio of NCM811 to LCO is 7:3, that is, 7.0 g of NCM811 powder and 3.0 g of LCO powder are weighed; the remaining steps and parameters are the same as in Example 1.

[0020] Example 3: A complementary strain NCM811 / LCO composite cathode for all-solid-state sulfide batteries differs from Example 1 in that: in step (1), the mass ratio of NCM811 to LCO is 6:4, that is, 6.0 g of NCM811 powder and 4.0 g of LCO powder are weighed; the remaining steps and parameters are the same as in Example 1.

[0021] Example 4: A complementary strain NCM811 / LCO composite cathode for all-solid-state sulfide batteries differs from Example 1 in that: in step (1), the mass ratio of NCM811 to LCO is 5:5, that is, 5.0 g of NCM811 powder and 5.0 g of LCO powder are weighed; the remaining steps and parameters are the same as in Example 1.

[0022] Comparative Example 1: A pure NCM811 positive electrode differs from Example 1 in that: in step (1), only 10.0 g of NCM811 powder is used as the positive electrode active material, and LCO is not added; the remaining steps and parameters are the same as in Example 1.

[0023] Comparative Example 2: A pure LCO positive electrode differs from Example 1 in that only 10.0 g of LCO powder is used as the positive electrode active material in step (1); the remaining steps and parameters are the same as in Example 1.

[0024] Performance testing and results analysis: The composite cathodes prepared in Examples 1-4 and Comparative Examples 1-2 were assembled with a Li6PS5Cl solid electrolyte layer and an In-Li alloy anode to form an all-solid-state sulfide battery, and their electrochemical performance was tested.

[0025] 1. First-cycle charge / discharge performance: Test conditions: room temperature, 0.1C rate, voltage range 2.0-3.7V.

[0026] Test results are as follows Figure 1 As shown, the results indicate that pure NCM811 (Comparative Example 1) exhibits the highest first-cycle discharge specific capacity (approximately 185 mAh / g), but the lowest coulombic efficiency (approximately 78%). This is due to the significant volume deformation of NCM811 during charge and discharge, leading to contact failure with the sulfide electrolyte, increased impedance, and partial capacity loss. With increasing LCO addition ratio, the first-cycle discharge specific capacity gradually decreases, but the coulombic efficiency significantly improves: Example 1 (8:2) has a coulombic efficiency of approximately 82%, Example 2 (7:3) approximately 86%, Example 3 (6:4) approximately 91%, and Example 4 (5:5) approximately 93%. Pure LCO (Comparative Example 2) has the highest coulombic efficiency (approximately 95%), but the lowest discharge specific capacity (approximately 140 mAh / g).

[0027] Considering the balance between discharge specific capacity and coulombic efficiency, Example 3 (6:4) performed best, maintaining a high discharge specific capacity of about 165 mAh / g while achieving a coulombic efficiency of about 91%.

[0028] 2. Ratio performance: Test conditions: room temperature, stepwise magnification tests at 0.1C, 0.2C, 0.5C, 1C, 2C, and 0.1C.

[0029] Test results are as follows Figure 2 As shown, the results indicate that Examples 2 (7:3) and 3 (6:4) exhibit excellent rate performance, especially at 0.5C and 1C rates, where the capacity retention is significantly higher than that of Comparative Example 1 (pure NCM811). Example 3 maintains a discharge specific capacity of approximately 120 mAh / g at 2C, while pure NCM811 only reaches approximately 95 mAh / g at 2C. This is because complementary mechanical deformation reduces electrode thickness variation, weakens overall stress fluctuations, and maintains good interfacial contact and ion transport channels. Example 4 (5:5) shows poor rate performance. Although excessive LCO improves interfacial stability, it severely limits the high-rate performance of NCM811, with the material's inherent electrochemical kinetics becoming the dominant factor.

[0030] 3. Long-term cycling performance: Test conditions: room temperature, 0.5C charge / discharge, voltage range 2.0-3.7V, 100 cycles.

[0031] Test results are as follows Figure 3 As shown, the results indicate that Examples 2 (7:3) and 3 (6:4) exhibit excellent long-term cycling stability at 0.5C. Example 3 showed a capacity retention of approximately 87% after 100 cycles, significantly higher than Comparative Example 1 (pure NCM811, approximately 68%). The superior performance of Example 3 is attributed to the optimal NCM811 to LCO ratio: effectively reducing shear and tensile stress concentration between particles and at the particle / electrolyte interface in terms of electrode mechanics, improving the contact retention ability of the solid-solid interface, and suppressing interfacial porosity formation; while maintaining the excellent electrochemical performance of the NCM811 material itself. Example 1 (8:2) showed limited strain compensation due to insufficient LCO content, resulting in only a slight improvement in cycling stability.

[0032] 4. Positive electrode morphology analysis after cycling: The cathodes of Example 3 and Comparative Example 1 were subjected to FIB (Focused Ion Beam) scanning electron microscopy analysis after 50 cycles at 0.5C.

[0033] Test results are as follows Figure 4As shown, the results indicate that after cycling, the positive electrode of Comparative Example 1 (pure NCM811) exhibits a large number of microcracks on the surface and inside of the positive electrode particles, and some particles break and pulverize. At the same time, there is obvious gap-like detachment between the positive electrode particles and the sulfide electrolyte, and the interfacial contact is severely deteriorated. This is the main reason for the rapid decline in its cycling performance.

[0034] In contrast, the composite cathode of Example 3 (NCM811:LCO=6:4) maintained high integrity and a significant reduction in the number of cracks after 50 cycles; the cathode particles maintained close contact with the sulfide electrolyte, and no obvious interfacial debonding or pore formation was observed. This directly demonstrates the effectiveness of complementary strain design in maintaining solid-solid interface stability.

[0035] 5. Impedance characteristic analysis: The DRT (relaxation time distribution) of Example 3 and Comparative Example 1 during the first charge and discharge cycle was analyzed, with a focus on the change of positive electrode charge transfer impedance (Rct) with voltage.

[0036] Test results are as follows Figure 5 As shown, the results indicate that Comparative Example 1 (pure NCM811) exhibits significant fluctuations in positive electrode charge transfer impedance during charging (2.05 V-3.7 V), with a notable peak in the 3.0-3.5 V range. This is because the NCM811 particles continuously shrink during charging, leading to increased porosity at the interface between the positive electrode active material and the electrolyte, reduced effective contact area, and increased interfacial impedance. Simultaneously, changes in lithium-ion concentration also affect the impedance distribution; the combined effect of these two factors results in substantial impedance fluctuations at different voltages.

[0037] In Example 3 (6:4 composite cathode), the charge transfer impedance of the cathode changed smoothly during the first charge cycle, with almost no significant fluctuations, only a slight increase around 3.2 V. This indicates that the overall deformation of the composite cathode was effectively suppressed during charging, maintaining good contact with the electrolyte. The impedance change mainly reflects the effect of changes in lithium-ion concentration, rather than interfacial contact failure. This is one of the key reasons why the battery exhibits excellent electrochemical performance.

[0038] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0039] Although embodiments of this application have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of this application, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A complementary strain NCM811 / LCO composite cathode for all-solid-state sulfide batteries, characterized in that, The active material of the composite cathode includes high-nickel ternary cathode material NCM811 and lithium cobalt oxide (LCO). The two are mixed by ball milling to form the composite cathode active material, and complementary strain is achieved by using opposite mechanical deformation laws.

2. The all-solid-state sulfide battery complementary strain NCM811 / LCO composite cathode according to claim 1, characterized in that, The mass ratio of the high-nickel ternary cathode material NCM811 to lithium cobalt oxide LCO is 50-80:20-50.

3. The all-solid-state sulfide battery complementary strain NCM811 / LCO composite cathode according to claim 1, characterized in that, The composite positive electrode also includes a sulfide solid electrolyte and a conductive agent, and the mass ratio of the composite positive electrode active material to the sulfide solid electrolyte and conductive agent is 5.5-6.5:3.8-4.2:0.08-0.

12.

4. The all-solid-state sulfide battery complementary strain NCM811 / LCO composite cathode according to claim 3, characterized in that, The sulfide solid electrolyte is Li6PS5Cl.

5. The all-solid-state sulfide battery complementary strain NCM811 / LCO composite cathode according to claim 3, characterized in that, The conductive agent is selected from at least one of conductive carbon black Super P, acetylene black, and carbon nanotubes.

6. The method for preparing the all-solid-state sulfide battery complementary strain NCM811 / LCO composite cathode as described in any one of claims 1-5, characterized in that, Includes the following steps: (1) Mix NCM811 powder and LCO powder in a mass ratio and ball mill at 150-350 rpm for 1-5 hours to obtain composite positive electrode active material; (2) The composite positive electrode active material is mixed with sulfide solid electrolyte and conductive agent to obtain composite positive electrode powder; (3) The composite cathode powder is cold-pressed to obtain the composite cathode layer.

7. The method for preparing the all-solid-state sulfide battery complementary strain NCM811 / LCO composite cathode according to claim 6, characterized in that, In step (1), the milling medium is zirconia balls, the ball-to-material mass ratio is 5-15:1, the milling time is 2-4 hours, and the milling speed is 200-300 rpm.

8. The method for preparing the all-solid-state sulfide battery complementary strain NCM811 / LCO composite cathode according to claim 6, characterized in that, The cold pressing pressure in step (3) is 300 MPa.

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