Kohei Shimokawa

Lithium (Li) metal anodes (LMAs) hold great promise to increase the energy density of batteries. This is especially true when using an energy‐dense cathode such as Ni‐rich layered transition metal oxides, but unfortunately, these lead to accelerated capacity loss when combined with LMAs. Ni‐rich cathodes suffer from surface reduction, which can be accelerated in contact with certain electrolyte solvents. This in turn leads to transition metal dissolution and shuttling, which poisons the solid electrolyte interphase (SEI) and complicates the anode stabilization. Here, we propose nitrile primary solvent combined with ether co‐solvent, diluent and two borate salts to suppress parasitic reaction. A competition in the ion coordination between solvents surrounded by diluents is achieved. This leads to the anions being preferentially decomposed in the SEI and enhanced reversibility. Using high cathode areal capacity (4.0 mAh cm ^{− 2} ), thin LMAs (N/p = 2.5), lean electrolyte (3 g Ah ^{− 1} ), and high charging voltages (≥4.4 V), we achieve a capacity retention of 80% over 250 cycles. With moderately high loading cathode (3.4 mAh cm ^{− 2} ) but higher upper voltage (4.6 V), the cells retain 87.5% capacity retention over 430 cycles. Finally, we demonstrate Ah‐level anode‐free pouch cells with a 78.7% capacity retention over 100 cycles.

Integrating solar energy conversion and storage into single-unit photobatteries offers compact energy supplies. However, achieving sufficient photovoltage to charge batteries without external bias remains a critical bottleneck for these devices. Here, we demonstrate that the photovoltage in Zn-ion photobatteries can be modulated and enhanced by selecting and structuring the photoactive materials strategically. Randomly dispersed electrode configurations are easy to manufacture but they can suffer from charge recombination. In our experiments, these yielded a negligible photovoltage of ∼0.01 V. In comparison, our proposed layer-by-layer design, integrating a solid-state dye-sensitized solar cell (DSSC) with an optimized spinel Zn–Mn oxide cathode, increased the photovoltage output to ∼1 V under 1-sun illumination. This dramatic performance enhancement is achieved by better control over interfaces and charge transport and establishes a strategy for improving the architecture of future photobatteries.

Lithium (Li) metal offers exceptional energy density but suffers from unstable interphases that lead to dendrite growth and poor reversibility. Because the interphase is established during the earliest stages of operation, controlling its formation is critical for stabilizing Li metal electrodes. Here, we demonstrate that a reflex charging strategy, in which short discharge pulses are introduced during charging, dynamically reprograms the interfacial environment. This approach sustains anion enrichment near the electrode surface and shifts Li ⁺ solvation from solvent‐dominated structures toward anion‐coordinated structures, thereby promoting the formation of an inorganic‐rich interphase. The resulting interphase reduces interfacial resistance and enables dense and uniform Li deposition. Consequently, the reflex charging‐based formation protocol exhibits markedly improved Li deposition/stripping reversibility, and greater resistance to degradation during cycling and calendar aging. In full cells paired with LiFePO ₄ (LFP) cathodes, the system retains 73% capacity after 500 cycles, demonstrating practical performance benefits. These findings establish formation protocol as an effective operation‐driven lever for controlling interfacial chemistry, offering a practical route that complements conventional materials‐based strategies for stabilizing Li metal batteries (LMBs).

Lithium (Li) metal offers exceptional energy density but suffers from unstable interphases that lead to dendrite growth and poor reversibility. Because the interphase is established during the earliest stages of operation, controlling its formation is critical for stabilizing Li metal electrodes. Here, we demonstrate that a reflex charging strategy, in which short discharge pulses are introduced during charging, dynamically reprograms the interfacial environment. This approach sustains anion enrichment near the electrode surface and shifts Li ⁺ solvation from solvent‐dominated structures toward anion‐coordinated structures, thereby promoting the formation of an inorganic‐rich interphase. The resulting interphase reduces interfacial resistance and enables dense and uniform Li deposition. Consequently, the reflex charging‐based formation protocol exhibits markedly improved Li deposition/stripping reversibility, and greater resistance to degradation during cycling and calendar aging. In full cells paired with LiFePO ₄ (LFP) cathodes, the system retains 73% capacity after 500 cycles, demonstrating practical performance benefits. These findings establish formation protocol as an effective operation‐driven lever for controlling interfacial chemistry, offering a practical route that complements conventional materials‐based strategies for stabilizing Li metal batteries (LMBs).

Electrochemical intercalation materials offer selective lithium recovery from saline streams, but conventional electrode architectures impose scale-up constraints. Here we report an electrode-free bioelectrochemical intercalation process in which a dissimilatory metal-reducing bacterium, Shewanella oneidensis MR-1, drives lithium uptake into λ-MnO₂. The system self-assembles into microbe–mineral agglomerates that sustain electrochemical-rate intercalation without external wiring, forming a recoverable lithiated slurry. Over 95% of lithium was recovered from seawater within hours, with less than 1% co-intercalation of competing metal ions. Bottom-up self-agglomeration, in which extracellular and cell-surface cytochromes facilitate efficient electron transfer, enables scale-up. The generality and energetic basis of this mechanism are further supported by reproducing the key behaviour in an orthogonal FePO₄ host with negligible abiotic reactivity. Techno-economic and life-cycle analyses for Li₂CO₃ production suggest that the process reduces brine water loss while maintaining competitive costs. These results establish self-assembled bioelectrochemical intercalation as a route to lithium recovery from saline streams.

Constructing sustainable energy systems requires rechargeable batteries with high safety, long cycle life and low production costs. Rechargeable magnesium batteries (RMBs) have been expected to be a promising candidate owing to low resource constraints compared to the commercial Li-based batteries. However, the development of RMBs have been stagnated after the first report of a prototype system, which consists of a Chevrel phase cathode, Mo₆S₈, and a Cl-based electrolyte.[1] The development of high potential oxide cathodes and non-corrosion Cl-free electrolyte encounters significant difficulties. Specifically, for oxide cathodes, the strong Coulomb interaction between Mg²⁺ and host structures usually inhibits the solid-state diffusion, causing a significant low discharge capacity compared to the theoretical value and rapid capacity loss during cycling.[2] Besides, non-corrosion electrolytes usually passivate Mg metal anodes and/or induce side reactions on oxide cathodes,[3] where remarkably decreases the cell voltage and accelerates the decomposition of electrolytes and active materials. In this presentation, we introduce our efforts to construct room-temperature RMBs with oxide cathodes and Cl-free electrolytes combining both the experimental and computational approaches. To explore suitable host structures for the topotactic Mg²⁺ intercalation, we revealed the phase transformation pathways and evaluated cathode properties of various transition oxide cathodes (e.g. MnO₂ polymorphs) at both elevated temperature (150℃) and room temperature.[3-6] Moreover, to assess the electrolyte compatibility, we discovered the connection between the solvation environment and the reaction behavior on both the oxide cathodes and Mg metal anodes.[3,7] These findings pave the way for room-temperature RMBs using oxide cathodes. [1] D. Aurbach et al, Nature 407, 724 (2000) [2] T. Ichitsubo et al, J. Mater. Chem. A 21, 11764 (2011) [3] X. Ye, H. Li, T. Ichitsubo et al, ACS Mater. Interfaces 14, 56685 (2022) [4] S. Okamoto, T. Ichitsubo et al, Adv. Sci. 2, 1500072 (2015) [5] K. Shimokawa, T. Ichitsubo et al, Adv. Mater. 33, 2007539 (2021) [6] T. Hayakeyama, H. Li, T. Ichitsubo et al, Chem. Mater. 33, 6983 (2021) [7] X. Ye, H. Li, T. Ichitsubo et al, submitted.

Oxide cathode materials are promising candidates for high-energy-density rechargeable magnesium batteries (RMBs) due to their high electrode potential. However, it is still challenging to reversibly insert/extract Mg into/from oxide cathodes since Mg insertion generally induces a partially irreversible phase transformation to a rocksalt structure (rocksalt transformation). This rocksalt transformation generally degrades the cyclability because the densely packed cations in the rocksalt structure impede the Mg migration. We reported that a defect spinel oxide of ZnMnO₃ successfully suppressed the rocksalt transformation within a limited capacity of ~70 mAh g^-1 [1]. However, the excessive Mg insertion resulted in the rocksalt transformation, limiting the available capacity. Elucidating the activation mechanism of the rocksalt oxide cathodes for RMBs is of great importance in circumventing this issue and ultimately utilizing rocksalt oxides themselves as promising cathode materials for RMBs. To tackle this problem, we designed a disordered-rocksalt oxide of Mg_0.35Li_0.3Cr_0.1Mn_0.05Fe_0.05Zn_0.05Mo_0.1O (M7O), in which initially contained Li is extracted in the first charging to yield substantial cation vacancies that facilitate the Mg migration in the structure, eventually activating the reversible Mg insertion/extraction in the subsequent cycles [2]. High configurational entropy derived from many constituent cations also plays a pivotal role. For example, high valence cations of Cr(III) and Mo(IV) do not solely form the rocksalt oxides. However, these elements were successfully incorporated into the structure. Furthermore, the formed vacancies were expected to be stabilized by high configurational entropy during the battery operation. The single-phase oxide of the disordered rocksalt structure was successfully synthesized using the Pechini method. The reversible discharge capacity of ~80 mAh g^-1 was constantly observed at a current density of 10.4 mA g^-1 at 90 °C. Inductively coupled plasma optical emission spectroscopy confirmed the Li extraction in the 1st charging and subsequent reversible Mg insertion/extraction via the cation vacancies formed by the Li extraction, which was further corroborated by X-ray diffraction. X-ray absorption spectroscopy indicated that Mn, Fe, and Mo compensate for the charge upon charging and discharging by changing their valence states, while those of Cr and Zn hardly changed. The ab initio calculations demonstrated that adjacent two cation vacancies significantly decrease the activation energy of the Mg migration in the rocksalt structure from ~2000 to 800 meV. The composition range to ensure that such a fast diffusion path is thoroughly connected in the particle was evaluated using the percolation theory. The present study opens a new frontier of the oxide cathodes for RMBs. [1] K. Shimokawa et al., Advanced Materials 33, 2007539 (2021). https://onlinelibrary.wiley.com/doi/10.1002/adma.202007539 [2] T. Kawaguchi et al., J. Mater. Chem. A (2024). https://pubs.rsc.org/en/content/articlelanding/2024/ta/d3ta07942b Image caption: (Left) Schematic of the reversible Mg insertion/extraction mechanism in the present rocksalt oxide cathode. (Top right) Energy dispersive spectroscopy images of the constituent elements. (Bottom right) Charge/discharge curves of the present cathode material. Figure 1

Oxide cathode materials have promising applications in rechargeable magnesium batteries (RMBs) due to their high redox potential, which allows the exploitation of the low potential of Mg metal anodes and the eventual realization of RMBs with high energy densities. However, the capacity and cyclability of oxide cathodes, such as spinel oxides, are frequently limited by the irreversible formation of rocksalt oxides during discharging because the rocksalt structure with densely packed cations hinders subsequent facile Mg extraction by charging, eventually leading to electrode deterioration. It is, therefore, of great importance to reveal a mechanism that realizes reversible Mg extraction/intercalation in rocksalt oxides to enhance the conventional oxide cathodes and exploit the rocksalt oxides as novel cathode materials for RMBs. Herein, we show an activation mechanism of rocksalt oxides as a cathode material for RMBs by exemplifying Li-extracted defect disordered rocksalt oxide obtained from Mg_0.35Li_0.3Cr_0.1Mn_0.05Fe_0.05Zn_0.05Mo_0.1O, which is capable of reversible Mg insertion/extraction. Extracting the Li cations in the first charging leads to a substantial amount of cation vacancies in the rocksalt structure, facilitating Mg diffusion in subsequent cycles. This vacancy is secured even after fully discharging the material by inserting Mg into the structure because of the lowest possible valence states of the constituent transition metal cations, contributing to the reversible charging/discharging of this material.

Stable photocharging has been demonstrated by applying an appropriate cation for spinel LiMn _1.5 M _0.5 O ₄ . This work paves the way for designing spinel-oxide cathode materials to develop high-performance photo-rechargeable batteries.