In a solid-state battery (SSB) system, undesirable electrode−electrolyte interfacial reactions lead to a significant performance degradation. Herein, we performed a systematic study on the chemical stabilities between Li 1.4 Al 0.4 Ti 1.6 (PO 4 ) 3 (LATP) solid electrolyte and various cathode materials at their adhesion temperatures of 500−900 °C. Quantitative analysis of X-ray diffraction (XRD) data using Rietveld refinement revealed that Li-concentration disparity between LATP and oxide cathode materials (e.g., layered and spinel phases) is the root cause of phase degradation at high temperatures. For example, Li migration from oxide cathodes to LATP produces multiple secondary phases including LiMPO 4 olivine. In contrast, the LiFePO 4 cathode severely reacted with LATP at low temperature (T < 500 °C) and produced an Fe-rich NASICON phase (e.g., Li 3 M 2 (PO 4 ) 3 ). The onset temperature of the phase decomposition varies with chemical compositions and crystal phases of cathodes. Increasing the cathode/electrolyte adhesion temperature offers a trade-off between the specific capacity and cycle life, as exemplified by the LiCoO 2 (LCO) + LATP composite cathodes. The results in this study offer a fundamental understanding of the LATP/cathode reaction mechanism, which will serve as guidance for designing interfaces and controlling the fabrication processes of SSB cells.

Understanding mechanochemical behaviors of binders facilitates the development of advanced binder materials to accelerate the adoption of Si-based anode materials. We demonstrated an approach to characterizing in-operando mechanical behaviors of binders while wetting in electrolyte solvents at nanoscale using atomic force microscopy (AFM). To reproduce Si–binder interfaces in anodes, we designed a model system and measured force spectroscopy between Si microcantilevers and binder films made with two representative materials: sodium (Na) alginate and poly­(vinylidene fluoride) (PVdF). Na-alginate has orders-of-magnitude higher adhesive forces with Si than PVdF after being immersed in dimethyl carbonate (DMC), which can be explained by (i) strong hydrogen bonds between Si surface’s oxidation layer and hydroxyl/carboxyl groups in Na-alginate and/or (ii) ion-dipole interactions between these two components. Na-alginate demonstrates a Young’s modulus ∼56 times greater than that of PVdF after several hours of immersion in DMC and reaching their steady-state conditions. The results correlate well with cycle life of Si anodes in battery cells considering that Na-alginate’s retention of mechanical strength and higher adhesive forces can help withstand the large volume expansions of Si.

Chemical composition – moisture sensitivity relationship of LiNixMnyCo1-x-yO2 (NMC) cathode materials was investigated by exploring crystal structures, surface properties and electrochemical performance behaviors of various commercial NMC powders: LiNi1/3Mn1/3Co1/3O2 (NMC111), LiNi0.5Mn0.3Co0.2O2 (NMC532), LiNi0.6Mn0.2Co0.2O2 (NMC622), and LiNi0.8Mn0.1Co0.1O2 (NMC811). The NMC powders were stored in different moisture conditions: moisture-free, humidified air, or immersed in water. Rietveld refinement analysis of X-ray diffraction (XRD) data and scanning electron microscopy (SEM) were used to characterize the crystal structure changes and the evolution of particle surfaces morphologies. The effect of moisture contamination on the electrochemical properties of NMC cathodes were studied by galvanostatic cycling and electrochemical impedance spectroscopy (EIS). The moisture contamination resulted in either structural disorder or unwanted surficial deposition products, which increased a charge-transfer impedance and consequent performance degradation of battery cells. The results showed that NMC's moisture vulnerability increased with Ni content (x) despite protective coatings on commercial particles, which stressed the necessity of alternative surface passivation strategies of Ni-rich NMC for broad applications such as electric vehicles (EVs) and electrified aircraft propulsion (EAP).

Positive roles of triethyl borate (TEB) electrolyte additive on high-voltage lithium-ion batteries were investigated in LiNi0.5Mn1.5O4(LNMO)/graphite full-cells. A capacity fading of the LNMO/graphite full-cells originates from the Mn dissolution of LNMO cathodes and a degradation of graphite SEI, which unwantedly consumes active Li+. Because the Li+ loss cannot be measured in a half-cell configuration (i.e., LNMO/Li), we designed a systematic experiment to understand the effect of TEB on the electrode–electrolyte interphases in the full-cells: cathode–electrolyte interphase (CEI) of LiNi0.5Mn1.5O4 (LNMO) and solid–electrolyte interphase (SEI) of graphite, respectively. Among various TEB contents (0–4 wt %) investigated, 1 wt % TEB offered combined advantages of high specific capacity and low full-cell impedance during extended cycling. The TEB contributed to the production of a CEI layer and suppressed Mn dissolution on LNMO cathode during long-term cycling. A combinatorial study of TEB-treated graphite and TEB-treated LNMO electrodes, however, suggested that an early-stage performance improvement shown by the full-cells was mostly contributed by an improved SEI stability on graphite anodes and a reduced Li+ loss, as evidenced by X-ray photoelectron spectroscopy data. Although literature data mostly focused on the impacts of TEB on CEI in half-cell configurations, our full-cell analyses revealed an additional benefit of TEB in significant improving stability of graphite SEI. Our results suggest that TEB can contribute to CEI and SEI simultaneously, which can offer promising performance improvements in various types of high-voltage LIBs.

Garnet-structured Li6.75La3Zr1.75Ta0.25O12 (LLZTO) is one of the most promising electrolyte materials for solid-state Li batteries (SS-LiB). The design and fabrication of a good cathode/electrolyte interface is an important criterion for the SS-LiB. In this work, we performed a systematic study on the impact of cathode crystal structure and chemical compositions on their chemical stabilities against the LLZTO at elevated temperatures, which are required for their adhesion during cell fabrication processes. X-ray Diffraction (XRD) and Rietveld refinement analyses revealed the chemical stabilities of various cathode materials in contact with the LLZTO. While layered LiCoO2 cathode showed good stability in contact with LLZTO to 900 oC, LiNiO2 or Ni-rich LiNixMnyCo1-x-yO2 (NMC) cathodes suffered from the formation of La4NiLiO8 due to La-diffusion from LLZTO. Mn-rich LiMn2O4 spinel and layered LiNi1/3Mn1/3Co1/3O2 cathodes suffered from the formation of La2Zr2O7 due to Li-diffusion and production of Li2MnO3. As a result, LiNi0.6Mn0.2Co0.2O2, having an ideal balance of Ni/Mn/Co composition, or Li2MnO3 containing cathodes such as Li1.2Ni0.15Mn0.55Co0.1O2 were found to having excellent phase stability as the cathodes for LLZTO-based SS-LiBs.