This study describes a high-energy and durable aqueous battery system with metastable and nanosized Mo-based oxides used as high-capacity negative electrodes. A wider electrochemical window is achieved with concentrated aqueous electrolytes through which highly reversible Li storage without the decomposition of water molecules is achieved for the Mo-based oxides. A full cell with an Mn-based oxide shows good capacity retention over 2,000 cycles. X-ray absorption spectroscopy reveals that the solid-state redox reaction of Mo ions reversibly proceeds in aqueous electrolytes for the metastable Mo oxide. This study opens a way to develop high-energy, durable, and safe batteries on the basis of metastable and nanosized oxides with aqueous electrolyte solutions.
The development of inherently safe energy devices is a key challenge, and aqueous Li-ion batteries draw large attention for this purpose. Due to the narrow electrochemical stable potential window of aqueous electrolytes, the energy density and the selection of negative electrode materials are significantly limited. For achieving durable and high-energy aqueous Li-ion batteries, the development of negative electrode materials exhibiting a large capacity and low potential without triggering decomposition of water is crucial. Herein, a type of a negative electrode material (i.e., LixNb2/7Mo3/7O2) is proposed for high-energy aqueous Li-ion batteries. LixNb2/7Mo3/7O2 delivers a large capacity of ∼170 mA ⋅ h ⋅ g−1 with a low operating potential range of 1.9 to 2.8 versus Li/Li+ in 21 m lithium bis(trifluoromethanesulfonyl)amide (LiTFSA) aqueous electrolyte. A full cell consisting of Li1.05Mn1.95O4/Li9/7Nb2/7Mo3/7O2 presents high energy density of 107 W ⋅ h ⋅ kg−1 as the maximum value in 21 m LiTFSA aqueous electrolyte, and 73% in capacity retention is achieved after 2,000 cycles. Furthermore, hard X-ray photoelectron spectroscopy study reveals that a protective surface layer is formed at the surface of the negative electrode, by which the high-energy and durable aqueous batteries are realized with LixNb2/7Mo3/7O2. This work combines a high capacity with a safe negative electrode material through delivering the Mo-based oxide with unique nanosized and metastable characters.
The demand for better rechargeable batteries is continuously increasing due to the penetration of electric vehicles (EVs) into the automotive market and the installation of stationary energy storage systems (ESSs) for renewable energy provision. For energy storage applications, Li-ion batteries (LIBs) are the best option thanks to their high energy density and efficiency (1). For instance, LIBs already power most of the state-of-the-art portable devices, and current EVs are equipped with 50 kWh of battery power to drive over 300 km on a single charge. Moreover, grid-scale ESSs should be operated at the megawatt-hour to gigawatt-hour level (2, 3). However, flammable organic electrolytes…