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1. Solid-state silicon anode with extremely high initial coulombic efficiency

   https://doi.org/10.1039/D2EE04057C  

   Huang, Yonglin; Shao, Bowen; Wang, Yan; Han, Fudong (April 2023, Energy & Environmental Science)

   Silicon is considered an important anode material for solid-state batteries (SSBs) because of its unique properties in addressing key challenges associated with Li metal anodes such as dendrite formation and morphological instability. Despite many exciting results from previous reports on solid-state Si anodes, the initial Coulombic efficiency (ICE), a critical parameter that characterizes the electrochemical reversibility for the first cycle and directly influences the energy density of the battery, has not been well considered. Here we study the electrochemical stability between Si and three representative solid electrolytes (SEs), including a typical sulfide (75Li 2 S-25P 2 S 5 , LPS), an iodide-substituted sulfide (70(0.75Li 2 S-0.25P 2 S 5 )-60LiI, LPSI), and a hydride-based SE (3LiBH 4 -LiI, LBHI), to improve the ICE of solid-state Si anodes. Combining first-principles computations, electrochemical measurements, ex situ XPS characterizations, and mechanical measurements, we report that LBHI demonstrates superior electrochemical and chemical stability with Si anodes compared with sulfide-based SEs, enabling a high-performance solid-state Si anode with a record high ICE of 96.2% among all Si anodes reported to date. The excellent stability of LBHI with Si anode was also demonstrated in solid-state full cells with nickel-rich layered oxide cathodes. The research provides novel insights into developing high-performance Si anodes for practical applications. 

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2. Multifunctional Li(Ni0.5Co0.2Mn0.3) O2-Si batteries with self-actuation and self-sensing

   Jun Ma, Cody Gonzalez (January 2020, Journal of intelligent material systems and structures)

   Among anode materials for Li-ion batteries, Si is known for high theoretical capacity, low cost, large volume change, relatively fast capacity fade and significant stress-potential coupling. This article shows that a Li(Ni0.5Co0.2Mn0.3)O2-Si battery can store energy, actuate with Si volume change and sense with stress-potential coupling. Experiments are conducted in an electrolyte-filled chamber with a glass window with Li(Ni0:5Co0:2Mn0:3)O2 cathodes and Si composite anodes. The Si anodes are single-side coated on Cu current collector with Si nanoparticles, polyacrylic acid binder and conductive carbon black in a porous composite structure. During charging, the battery stores energy, Li inserts in the cantilevered Si anodes and the cantilevers bend laterally. Discharging the battery releases the stored energy and straightens the Si cantilevers. Imposing deformation on the Si cantilevers at a fixed state of charge causes bending stress in the composite coating and a change in the open circuit potential. Testing at 1Hz confirms that the Si composite responds to dynamic stress variations and with almost no phase lag, indicating the bandwidth of the stress-potential coupling in Si composite anodes is at least 1Hz. 

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3. Universal Cathode Design Strategies to Engineer Cathode Electrolyte Interfaces for High Performance All-Solid-State Batteries

   Zhang, Yuxuan; Song, Han Wook; Lee, Sunghwan (May 2022, Materials Research Society)

   Metal-ion batteries (e.g., lithium and sodium ion batteries) are the promising power sources for portable electronics, electric vehicles, and smart grids. Recent metal-ion batteries with organic liquid electrolytes still suffer from safety issues regarding inflammability and insufficient lifetime.1 As the next generation energy storage devices, all-solid-state batteries (ASSBs) have promising potentials for the improved safety, higher energy density, and longer cycle life than conventional Li-ion batteries.2 The nonflammable solid electrolytes (SEs), where only Li ions are mobile, could prevent battery combustion and explosion since the side reactions that cause safety issues as well as degradation of the battery performance are largely suppressed. However, their practical application is hampered by the high resistance arising at the solid–solid electrode–electrolyte interface (including cathode-electrolyte interface and anode-electrolyte interface).3 Several methods have been introduced to optimize the contact capability as well as the electrochemical/chemical stability between the metal anodes (i.e.: Li and Na) and the SEs, which exhibited decent results in decreasing the charge transfer resistance and broadening the range of the stable energy window (i.e., lowing the chemical potential of metal anode below the highest occupied molecular orbital of the SEs).4 Nevertheless, mitigation for the cathode in ASSB is tardily developed because: (1) the porous structure of the cathode is hard to be infiltrated by SEs;5 (2) SEs would be oxidized and decomposed by the high valence state elements at the surface of the cathode at high state of charge.5 Herein, we demonstrate a universal cathode design strategy to achieve superior contact capability and high electrochemical/chemical stability with SEs. Stereolithography is adopted as a manufacturing technique to realize a hierarchical three-dimensional (HTD) electrode architecture with micro-size channels, which is expected to provide larger contact areas with SEs. Then, the manufactured cathode is sintered at 700 °C in a reducing atmosphere (e.g.: H2) to accomplish the carbonization of the resin, delivering sufficiently high electronic conductivity for the cathode. To avoid the direct exposure of the cathode active materials to the SEs, oxidative chemical vapor deposition technique (oCVD) is leveraged to build conformal and highly conducting poly(3,4-ethylenedioxythiophene) (PEDOT) on the surface of the HTD cathode.6 To demonstrate our design strategy, both NCM811 and Na3V2(PO4)3 is selected as active materials in the HTD cathode, then each cathode is paired with organic (polyacrylonitrile-based) and inorganic (sulfur-based) SEs assembled into two batteries (total four batteries). SEM and TEM reveal the micro-size HTD structure with built-in channels. Featured by the HTD architecture, the intrinsic kinetic and thermodynamic conditions will be enhanced by larger surface contact areas, more active sites, improved infusion and electrolyte ion accessibility, and larger volume expansion capability. Disclosed by X-ray computed tomography, the interface between cathode and SEs in the four modified samples demonstrates higher homogeneity at the interface between the cathode and SEs than that of all other pristine samples. Atomic force microscopy is employed to measure the potential image of the cross-sectional interface by the peak force tapping mode. The average potential of modified samples is lower than that of pristine samples, which confirms a weakened space charge layer by the enhanced contact capability. In addition, through Electron Energy Loss Spectroscopy coupled with Scanning Transmission Electron Microscopy, the preserved interface between HTD cathode and SE is identified; however, the decomposing of the pristine cathode is clearly observed. In addition, Finite element method simulations validate that the diffusion dynamics of lithium ions is favored by HTD structure. Such a demonstrated universal strategy provides a new guideline to engineer cathode electrolyte interface by reconstructing electrode structures that can be applicable to all solid-state batteries in a wide range of chemical conditions. 

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4. Electrodeposited thin-film Cu _x Sb anodes for Li-ion batteries: enhancement of cycle life via tuning of film composition and engineering of the film-substrate interface

   https://doi.org/10.1039/c8ta01798k  

   Schulze, Maxwell C.; Schulze, Roland K.; Prieto, Amy L. (January 2018, Journal of Materials Chemistry A)

   Electrodeposited Cu–Sb thin films on Cu and Ni substrates are investigated as alloy anodes for Li-ion batteries to elucidate the effects of both the film composition and substrate interactions on anode cycling stability and lifetime. Thin films of composition Cu x Sb (0 < x < 2) exhibit the longest cycle lifetimes nearest x = 1. Additionally, the Cu–Sb films exhibit shorter cycle lifetimes when electrodeposited onto Cu substrates when compared to equivalent films on Ni substrates. Ex situ characterization and differential capacity analysis of the anodes reveal that significant interdiffusion occurs during cycling between pure Sb films and Cu substrates. The great extent of interdiffusion results in mechanical weakening of the film–substrate interface that exacerbates film delamination and decreases cycle lifetimes of Cu–Sb films on Cu substrates regardless of the film's composition. The results presented here demonstrate that the composition of the anode alone is not the most important predictor of long term cycle stability; the composition coupled with the identity of the substrate is key. These interactions are critical to understand in the design of high capacity, large volume change materials fabricated without the need for additional binders. 

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5. A niobium oxide with a shear structure and planar defects for high-power lithium ion batteries

   https://doi.org/10.1039/D1EE02664J  

   Li, Tongtong; Nam, Gyutae; Liu, Kuanting; Wang, Jeng-Han; Zhao, Bote; Ding, Yong; Soule, Luke; Avdeev, Maxim; Luo, Zheyu; Zhang, Weilin; et al (January 2022, Energy & Environmental Science)

   The development of anode materials with high-rate capability is critical to high-power lithium batteries. T-Nb 2 O 5 has been widely reported to exhibit pseudocapacitive behavior and fast lithium storage capability. However, the other polymorphs of Nb 2 O 5 prepared at higher temperatures have the potential to achieve even higher specific capacity and tap density than T-Nb 2 O 5 , offering higher volumetric power and energy density. Here, micrometer-sized H-Nb 2 O 5 with rich Wadsley planar defects (denoted as d-H-Nb 2 O 5 ) is designed for fast lithium storage. The performance of H-Nb 2 O 5 with local rearrangements of [NbO 6 ] octahedra blocks surpasses that of T-Nb 2 O 5 in terms of specific capacity, rate capability, and stability. A wide range variation in the valence of niobium ions upon lithiation was observed for defective H-Nb 2 O 5 via operando X-ray absorption spectroscopy. Operando extended X-ray absorption fine structure and ex situ Raman spectroscopy analyses reveal a large and reversible distortion of the structure in the two-phase region. Computation and ex situ X-ray diffraction analysis reveal that the shear structure expands along major lithium diffusion pathways and contracts in the direction perpendicular to the shear plane. Planar defects relieve strain through perpendicular arrangements of blocks, minimizing volume change and enhancing structural stability. In addition, strong Li adsorption on planar defects enlarges intercalation capacity. Different from nanostructure engineering, our strategy to modify the planar defects in the bulk phase can effectively improve the intrinsic properties. The findings in this work offer new insights into the design of fast Li-ion storage materials in micrometer sizes through defect engineering, and the strategy is applicable to the material discovery for other energy-related applications. 

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