Interface compatibility between sulfide solid electrolytes and Ni-rich oxide cathode materials: factors, modification, perspectives

Surface to bulk design empowering Ni-rich layered oxide cathode in sulfide-based All-Solid-State batteries

Enabling stable and high areal capacity solid state battery with Ni-rich cathode via failure mechanism study

As the electric vehicles (EVs) market is growing rapidly, lithium ion batteries (LIBs) have received great attention as a suitable power source owing to its high-energy density and excellent power characteristic. To extend a driving mileage of the EVs, it is crucial to further improve the energy density of LIBs. Since the specific capacity and operating voltage of cathode materials are important factors for determining the energy density of LIBs, many researches focus on the development of advanced cathode materials with high specific capacity and high operating voltage. Among various cathode materials, layered cathode materials (e.g., LiMO2, M = transition metal) have been one of the most popular cathode materials in LIBs. The electrochemical properties of these cathode materials are tunable by the choice of transition metals in the host structure; i) Mn secures structural stability, ii) Co increases power characteristic, and iii) Ni contributes to a specific capacity of the materials. In order to increase the achievable specific capacity, researchers have designed the layered cathode materials with a high Ni content (>80%) and they offer a high reversible capacity more than 190 mA h g-1. Unfortunately, Ni-rich layered cathode materials suffer from poor thermal and structural stabilities arising from the high Ni content in the structure. To overcome these limitations, therefore, structural modifications on the Ni-rich cathode materials is highly required to suppress undesirable side reactions and formations of impurities (e.g., NiO). Herein, we prepare Mn surface-doped NCM811 (Mn-NCM811) with a core-shell structure via a simple wet-coating process using lithium ethoxide and Mn acetate precursors. Various structural and electrochemical investigations support that Mn-rich shell can effectively improve the structural and thermal stabilities of Ni-rich core, leading to the significant improvement in electrochemical performance of Ni-rich layered cathode materials even at a high operating temperature of 60 °C. From the results, we emphasize the importance of material design and this study will provide practical guidelines for development of Ni-rich layered cathode materials for LIBs.

All-solid-state batteries (ASSBs) using sulfide solid electrolytes with high room-temperature ionic conductivity are expected as promising next-generation batteries, which might solve the safety issues and enable the utilization of lithium metal as the anode to further increase the energy density of cells. Most researchers in the academic community currently focus on developing novel sulfide solid electrolytes, clarifying the interface issues between sulfide electrolytes and solid electrodes and mechanism of lithium dendrite growth in ASSB. However, there is a lacking in the technical route analysis about the commercialization of ASSBs based on sulfide solid electrolytes. This review mainly introduces the specific preparation methods of various parts in sulfide-based ASSBs, including the preparation methods of sulfide solid electrolyte particles, sulfide-based composite electrolyte membranes, composite cathodes and anodes, and analyzes the advantages and disadvantages of these methods. In addition, several schemes of ASSB assembly are also introduced. Finally, a perspective of large-scale production of sulfide-based ASSBs is provided, which is expected to accelerate the commercialization of sulfide-based ASSBs.

One of the more promising cathode materials for high-energy high-voltage lithium ion batteries (LIBs) are Ni-rich layered cathode materials such as LiNixMnyCozO2 (where x + y + z = 1). Although these cathode materials are attractive from a high capacity standpoint, they commonly suffer from poor structural stability at highly delithiated (charged) states leading to poor electrochemical performance.1-3 To help aid these issues, surface coatings are becoming a widely adopted method to improve the cycling performance of high-voltage cathode materials. More widely investigated coating materials include oxide coatings (Al2O3, TiO2, etc.)4 while comparatively fewer studies have investigated organic monomer or polymer coatings (PEDOT, polyimide, etc.).5 In this work, the surface of LiNi0.5Mn0.3Co0.2O2 cathode materials were coated with organosilane reagents to investigate their effect on cell electrochemical performance. The impact of the weight percentage of organosilane used and the functionality of the organosilane used will be presented. Characterization of the organosilane coating using XRD, XPS and FTIR confirm the presence of a Si-containing coating. Cycling performance for half cells (Li/ LiNi0.5Mn0.3Co0.2O2) using the organosilane coated cathodes will be shown. In conclusion, a new type of organic coating was utilized on Ni-rich cathode materials and this research explores a new type of coating for high voltage cathodes. 1) Son, I. H.; Park, J. H.; Kwon, S.; Mun, J. and Choi, J. W. Chem. Mat. 2015, 27, 7370-7379. 2) Bak, S.-M.; Hu, E.; Zhou, Y.; Yu, X.; Senanayake, S. D.; Cho, S.-J.; Kim, K.-B.; Chung, K. Y.; Yang, X.-Q. and Nam, K.-W. ACS Appl. Mater. Interfaces 2014, 6, 22594-22601. 3) Lin, F.; Markus, I. M.; Doeff, M. M.; Xin, H. L. Sci. Rep., 2014, 4, 5694. 4) Xu, S.; Jacobs, R. M.; Nguyen, H. M.; Hao, S.; Mahanthappa, M.; Wolverton, C.; Morgan, D. J. Mater. Chem. A, 2015, 3, 17248. 5) Zhang, J.; Lu, Q.; Fang, J.; Wang, J.; Yang, J. and NuLi, Y. ACS Appl. Mater. Interfaces 2014, 6, 17965-17973.

Sulfide-based all-solid-state batteries (ASSBs) have ushered in a new era of energy storage technology, offering the tantalizing prospect of unprecedented energy density and safety. However, the poor electrode-electrolyte interface between Li anodes and sulfide solid electrolytes has hindered its practical application. In this review, the primary focus lies in the current fundamental understanding, challenges, and optimization strategies regarding the interface chemistries between sulfide solid electrolytes and Li anode. First, an in-depth discussion is conducted and provides a detailed summary of the interfacial challenges that exist between the Li anode and sulfide solid electrolytes. Among these challenges, poor interfacial compatibility and stability stand out as the two crucial issues. Subsequently, effective approaches are systematically explored to surmount these issues. These encompass the component optimization and structural design of the bulk anode, doping and coating strategies of the sulfide solid electrolytes, and interface design between the Li anode and sulfide solid electrolytes. Finally, the insights are present into the limitations of current studies, perspectives, and recommendations for the further development of sulfide-based solid-state batteries, aiming to offer a comprehensive and enlightening overview for interface engineering, which is of great significance for the integration of applicable all-solid-state Li metal batteries (ASSLMBs).

All-solid-state batteries (ASSBs) working at room and mild temperature have demonstrated inspiring performances over recent years. However, the kinetic attributes of the interface applicable to the subzero temperatures are still unidentified, restricting the low-temperature interface design and operation. Herein, a host of cathode interfaces are constructed and investigated to unlock the critical interface features required for cryogenic temperatures. The unstable interface between LiNi0.90Co0.05Mn0.05O2 (Ni90) and Li6PS5Cl (LPSC) sulfide solid electrolyte (SE) results in unfavorable cathode-electrolyte interphase (CEI) and sluggish lithium-ion transport across the CEI. After inserting a Li2ZrO3 (LZO) coating layer, the activation energy of the Ni90@LZO/sulfide SE interface can be reduced from 60.19 kJ mol-1 to 41.39 kJ mol-1 owing to the suppressed interfacial reactions. Through replacing the LPSC SE and LZO coating layer by the Li3InCl6 (LIC) halide SE, both a highly stable interface and low activation energy (25.79 kJ mol-1) can be achieved, thus realizing an improved capacity retention (26.9%) at -30 °C for the Ni90/LIC/LPSC/Li-In ASSB. Moreover, theoretical evaluation clarifies that cathode/SE interfaces with high ionic conductivity and low energy barrier are favorable to the Li+ conduction through the interphase and the Li+ transfer across the cathode/interphase interface. These critical understandings may provide guidance for low-temperature interface design in ASSBs.

Due to the high capacity and the high discharge potential, Ni-rich layered cathode materials are considered as a class of promising cathode material and attracting considerable attention. Because of the Li+/Ni2+ cation mixing, Li residues, overcharging, crystal orientation of the secondary particles, poor cycling stability and rate capability are usually received in lithium ion batteries. In this presentation, we introduce a layered NMC811 with Ni-gradients by using metal-organic framework (MOF) as precursor ( Cell Reports Physical Science , 3 (2022), 100767). The self-healing phase by forming a cation mixing layer on the surface of particles effectively improved the structural stability by suppressing the phase transition and internal cracks upon cycling. In the half-cell battery, an initial capacity of 203.5 mAh/g at 0.1 C and a capacity retention of 88.5% after 300 cycles at 1/3 C were obtained. The battery still showed a CE of 99.47% at 1/3 C after 300 cycles at 55 ℃. In addition, the full-cell battery showed a capacity retention of >86.7% with a CE of >99.86% at 1/3 C after 300 cycles. Moreover, a pouch cell delivered an initial capacity of 297.62 mAh and a CE of 99.48%, which contributed to an energy density of 216.41 Wh/kg. The capacity retention was still as high as 84.1% after 500 cycles at 1.0 C. Keywords: Li-ion batteries; Ni-rich cathode materials; MOF; Concentration gradient

Dually-functionalized Ni-rich layered oxides for high-capacity lithium-ion batteries

Stabilizing the interface between high-Ni oxide cathode and Li6PS5Cl for all-solid-state batteries via dual-compatible halides

Analyzing the effect of Li/Ni intermixing on Ni-rich layered cathode structures using atomistic simulation of the Li–Ni–Mn–Co–O quinary system

Outstanding interfacial issues exist between oxide cathodes and sulfide electrolytes in all‐solid‐state lithium batteries (ASSLBs), while high‐capacity Li‐rich sulfide cathodes are gaining attention for application. Herein, a sulfide cathode active material Li2TiS3 (LTS) that is chemically compatible with sulfide solid electrolytes, is used in high‐performance Li6PS5Cl‐based ASSLBs at room temperature. The batteries demonstrate a maximum discharge capacity of 423.2 mAh g−1 (910 Wh kg−1 based on Li2TiS3) with 95% capacity retention after 100 cycles at 0.1 C (0.33 mA cm−2). Traces of elemental sulfur on the surface of LTS are mainly responsible for the excessive Li‐intercalation and the capacity exceedance. The Li6PS5Cl is also found to offer a nonnegligible capacity (at least 27% of excess capacity) by comparing the Li6PS5Cl‐based and Li3YCl6‐based cells using Li2TiS3 as cathode active material. During long cycling, the amorphization and degradation of Li2TiS3 and Li6PS5Cl cause capacity decay. The electrochemical kinetics of Li6PS5Cl‐based cells are evaluated as a reference to further exploit the potential of Li2TiS3 material for practical applications in ASSLBs. Overall, this superior Li‐rich sulfide material is an attractive alternative to oxide cathodes for the development of high‐performance ASSLBs.

An Ostwald ripening-based route is proposed to prepare Ni-rich layered cathodes with Co-rich surface for lithium-ion batteries (LIBs). Commercially available Ni0.8Co0.1Mn0.1(OH)2 and spray pyrolysis derived porous Co3O4 are used as mixed precursors. During the lithiation reaction process under high-temperature, the porous Co3O4 microspheres scatter primary particles and spontaneously redeposit on the surface of Ni-rich spheres according to Ostwald ripening mechanism, forming the Ni-rich materials with Co-rich outer layers. When evaluated as cathode for LIBs, the resultant material shows ability to inhibit the cation disorder, relieves the phase transition from H2 to H3 and diminishes side reactions between the electrolyte and Ni-rich cathode material. As a result, the obtained material with Co-rich outer layers exhibits much more improved cycle and rate performance than the material without Co-rich outer layers. Particularly, NCM-Co-1 (molar ratio of Ni0.8Co0.1Mn0.1(OH)2/Co3O4 is 60:1) delivers a reversible capacity of 159.2 mA h g−1 with 90.5% capacity retention after 200 cycles at 1 C. This strategy provides a general and efficient way to produce gradient substances and to address the surface problems of Ni-rich cathode materials.

Resynthesis of Ni-rich lithium nickel manganese cobalt oxide cathode materials from the industrial leachate of spent Li-ion batteries: The effect of PF6− species from electrolyte

Superionic sulfide solid electrolytes (SEs) are of considerable interest for application in solid‐state batteries, but suffer from limited stability. When in combination with state‐of‐the‐art cathode active materials (CAMs), severe degradation at the CAM/SE interface occurs during electrochemical cycling. To improve upon the interfacial stability, inert coatings can be applied to the CAM particles, with the goal of preventing direct contact to the SE. In this study, different methods of depositing coatings, including hexagonal boron nitride, tungsten sulfide and exfoliated ((CH3(CH2)3)4N)4Nb6O17, in the form of nanosheets onto the free surface of a Ni‐rich LiNixCoyMnzO2 (NCM) CAM are examined and compared with one another. While dry coating is shown to produce relatively uniform coatings (good surface coverage), the secondary particle morphology of the NCM makes ball milling as a mechanical deposition method less attractive. In contrast, deposition from dispersions in organic solvents yields protective coatings with a lower degree of surface coverage. The different materials are electrochemically tested in liquid‐ and solid‐electrolyte‐based lithium‐ion batteries. A stabilizing effect from nanosheet coating is only observed for the cells with lithium thiophosphate SE.