Charge–discharge properties of LiMn₂O₄-group positive electrode active materials for lithium-ion batteries using high-throughput experimental screening and machine learning models

To improve the charge – discharge properties of an LiMn2O4 positive electrode active material for a lithium-ion battery, the effect of additive elements was investigated using high-throughput experiments and materials informatics techniques. First, the material libraries of LiMn1.4NixAyBzO4±δ (A, B = Mo, Ir, Bi, Eu, Zn, Y, Ce, and Ru, x + y + z = 0.6, x, y, z = 0, 0.2, 0.4, 0.6) were synthesized by the ink-jet technique, and the properties were estimated using X-ray diffraction and X-ray absorption near-edge structure (XANES) spectroscopy at SPring-8. Appropriate additives were searched for by machine learning models using composition-based explanatory and experimentally obtained objective variables without completing the lithium-ion battery cell. Next, LiMn2O4 specimens containing the additives were synthesized by the solid-state reaction method, and then the charge – discharge properties were verified using the sandwich-type electrochemical cell. Based on the results, LiMn1.6Ni0.2Ir0.1Mo0.1O4±δ, LiMn1.6Ni0.2Pd0.1W0.1O4±δ, LiMn1.6Ni0.2Ir0.1W0.1O4±δ, LiMn1.6Ni0.3W0.1O4±δ, and LiMn1.6Ni0.2Ru0.1W0.1O4±δ had approximately 10% larger current capacity and approximately 0.1 V higher average charge – discharge potential than LiMn2O4 without additives. The charge compensation of lithiation and delithiation could be caused by the valence change of Mn (Mn4+ ⇌ Mn3+) and Ni ions (Ni3+ ⇌ Ni2+), which was estimated by XANES spectroscopy. The appropriate additives for LiMn2O4-based materials (cathode material for LIBs) were searched for using high-throughput experiments and machine learning without the laborious fabrication of electrochemical cells</p

Water in Ionic Liquid for Electrochemical Li Cycling

A solution of water in ionic liquid was tested as a practical electrolyte for Li–air batteries. Li metal deposition and stripping were repeatedly performed with an acceptable polarization voltage (<±250 mV) even under 1 vol % of water in the ionic liquid electrolyte. Such an advantageous performance was explained by XPS surface analysis on a Li metal after cycling and the thermodynamic state of water in ionic liquid as a bulk electrolyte. Remarkably, the chemical species (LiF and LiOH) forming at the Li/electrolyte interface did not evolve through the addition of water, suggesting that water did not exist as free water that intensively reacts with Li metal. Furthermore, free water was not thermally observed in the ionic liquid electrolyte, indicating that water may be bound to the electrolyte. The water in an ionic liquid will become a new avenue to design the water-tolerant electrolyte against Li metal

Intrinsic Barrier to Electrochemically Decompose Li₂CO₃ and LiOH

It is widely acknowledged that Li₂CO₃ and LiOH as side-products in the operation of a Li–air cell should be completely removed in the cycling to avoid cumulative negative effect on the cycling performance. However, the understanding of their electrochemical decomposition is limited. We report a mechanistic analysis of the intrinsic barrier to electrochemically decompose Li₂CO₃ and LiOH. Our first-principles study reveals that the decomposition is rate-limited by the electrochemical extraction of Li⁺, whereas the chemical release of anions is barrierless once the applied voltage overcomes the energy penalty to generate a Li-deficient surface. The voltage necessary for the decomposition of Li₂CO₃ is predicted to be in the range of 4.38–4.61 V, whereas for LiOH it is in the range of 4.67–5.02 V. The maximum charge efficiency to decompose Li₂CO₃ and LiOH in the operation of a Li–air cell is estimated to be 66% and 61%, respectively. The high intrinsic barrier originates from the energy cost of oxidizing redox-inert anions for the charge neutrality when lithium is extracted. Therefore, one strategy for lowering the barrier is incorporating redox-active species as a charge mediator to compensate the electron loss during the decomposition

Investigation of the Relationship between Solvation Structure and Battery Performance in Highly Concentrated Aqueous Nitroxy Radical Catholyte

A new battery catholyte material composed of equimolar 4-methoxy-2,2,6,6-tetramethylpiperidine 1-oxyl (MT) and lithium bis­(trifluoromethanesulfonyl) imide (LT) and its highly concentrated mixtures with water were studied using experiments and molecular dynamics simulations. It was found that the dynamic properties of the mixture are significantly improved by adding even a small amount of water. Detailed analysis on the solvation structure in the mixtures reveals that water molecules can break the strong interaction between MT and LT, and thus the ions can move more freely. As a result, the ionic conductivity of the catholyte mixtures increases with increasing water molar ratio in the water concentration range covered in the current work. The performance of the catholyte mixture systems was also tested in battery cells. The best utility efficiency of the capacity was found for the mixture of water:MT:LT ratio at 5.3:1:1. Water molar ratios of 5 to 6 were also found to be the lowest concentration at which MT and LT are fully saturated by water. These results provide insightful understanding of the performance of these battery catholytes

Catalytic Cycle Employing a TEMPO–Anion Complex to Obtain a Secondary Mg–O₂ Battery

Nonaqueous Mg–O₂ batteries are suitable only as primary cells because MgO precipitates formed during discharging are not decomposed electrochemically at ambient temperatures. To address this problem, the present study examined the ability of the 2,2,6,6-tetramethylpiperidine-oxyl (TEMPO)–anion complex to catalyze the decomposition of MgO. It was determined that this complex was capable of chemically decomposing MgO at 60 °C. A catalytic cycle for the realization of a rechargeable Mg–O₂ electrode was designed by combining the decomposition of MgO via the TEMPO–anion complex and the TEMPO–redox couple. This work also demonstrates that a nonaqueous Mg–O₂ battery incorporating acrylate polymer having TEMPO side units in the cathode shows evidence of being rechargeable