Transition-metal compounds (oxides, sulfides, hydroxides, etc.) as lithium-ion battery (LIB) anodes usually show extraordinary capacity larger than the theoretical value due to the transformation of LiOH into Li2O/LiH. However, there has rarely been a report relaying the transformation of LiOH into Li2O/LiH as the main reaction for LIBs, due to the strong alkalinity of LiOH leading to battery deterioration. In this work, layered silicate MgAl saponite (MA-SAP) is applied as a −OH donor to generate LiOH as the anode material of LIBs for the first time. The MA-SAP maintains a layered structure during the (dis)charging process and has zero-strain characteristic on the (001) crystal plane. In the discharging process, Mg, Al, and Si in the saponite sheets become electron-rich, while the active hydroxyl groups escape from the sheets and combine with lithium ions to form LiOH in the “caves” on sheets, and the LiOH continues to decompose into Li2O and LiH. Consequently, the MA-SAP delivers a maximum capacity of 536 mA h·g–1 at 200 mA·g–1 with a good high-current discharging ability of 155 mA h·g–1 after 1000 cycles under 1 A·g–1. Considering its extremely low cost and completely nontoxic characteristics, MA-SAP has great application prospects in energy storage. In addition, this work has an enlightening effect on the development of new anodes based on extraordinary mechanisms.

Anode materials with simultaneously large capacity and low working voltage have always been one of the pursuing goals in the development of lithium-ion batteries. In this report, erdite NaFeS2 was synthesized by phase conversion of Fe-saponite for the first time, which displays attractive lithium-storage performance as an anode material. Taking into consideration that NaFeS2 can be regarded as sodium pre-embedded FeS2, a thorough comparison of lithium-storage performance between NaFeS2 and FeS2 was carried out. Theoretical calculation reveals that NaFeS2 has metallic conductivity and thus faster electron transfer than FeS2. The main oxidation and reduction peaks of the NaFeS2/Li battery reduce by 0.4–0.8 V compared with those of FeS2/Li, which are qualitatively supported by density functional theory calculations. Additionally, NaFeS2 delivers higher capacity, longer cycle life (1157 mAh·g–1 after 500 cycles), and better rate performance (618 mAh·g–1 at 5 A·g–1) than FeS2. Significantly decreased (de)­lithiation voltage and increased capacity through changing the electrochemical reaction mechanism are favorable for improving the energy and power density of the batteries. This work develops a facile method of transforming silicate into sulfide and puts forward a strategy to reduce the (de)­lithiation voltage of high-capacity anode materials, which is meaningful for boosting energy/power densities of energy storage devices.

A fluoride-ion battery (FIB) is a novel type of energy storage system that has a higher volumetric energy density and low cost. However, the high working temperature (>150 °C) and unsatisfactory cycling performance of cathode materials are not favorable for their practical application. Herein, fluoride ion-intercalated CoFe layered double hydroxide (LDH) (CoFe-F LDH) was prepared by a facile co-precipitation approach combined with ion-exchange. The CoFe-F LDH shows a reversible capacity of ∼50 mAh g–1 after 100 cycles at room temperature. Although there is still a big gap between FIBs and lithium-ion batteries, the CoFe-F LDH is superior to most cathode materials for FIBs. Another important advantage of CoFe-F LDH FIBs is that they can work at room temperature, which has been rarely achieved in previous reports. The superior performance stems from the unique topochemical transformation property and small volume change (∼0.82%) of LDH in electrochemical cycles. Such a tiny volume change makes LDH a zero-strain cathode material for FIBs. The 2D diffusion pathways and weak interaction between fluoride ions and host layers facilitate the de/intercalation of fluoride ions, accompanied by the chemical state changes of Co2+/Co3+ and Fe2+/Fe3+ couples. First-principles calculations also reveal a low F– diffusion barrier during the cyclic process. These findings expand the application field of LDH materials and propose a novel avenue for the designs of cathode materials toward room-temperature FIBs.

A hierarchical structure is successfully synthesized by coating polypyrrole (PPy) on the surface of carbon/saponite superlattice (denoted as PPy@C/SAP), and applied as low volume‐expansion insertion‐type anode for Li, Na, K storage.The synergistic effect of metal Ni, Fe doping, carbon/silicate superlattice, abundant oxygen vacancies and PPy coating leads to a good electronic conductivity and large current discharging capability. As a Si‐based material, PPy@C/SAP has excellent storage capability for Li (659 mAh g−1 after 1000 cycles at 2 A g−1 and 550 mAh g−1 after 1000 cycles at 5 A g−1), Na (maximum specific capacity of 533 and 327 mAh g−1 after 50 cycles) as well as K (236 mAh g−1 after 100 cycles). XPS, XANES, XRD, FTIR, HRTEM, SEM are used to detect the hybrid mechanism (bulk insertion and surface conversion) with a volume expansion as low as 9%. Insertion reaction driven by valence state change of Ni, Fe, Si (Ni0⇔Ni2+, Fe0⇔Fe3+, Si2+⇔Si4+) in laminates and conversion reactions between LiOH/Li2CO3 and LiH/Li2C2 catalyzed by Ni° contribute to the high performance. In the whole electrochemical process, layered structure is retained while the conversion reactions of LiOH (prodeced by laminates dehydroxylation) and Li2CO3 (electrolyte decomposition) cause the dynamic evolution of solid ectrolyte interphase. This study develops a promising Si‐based anode material for lithium ion batteries, sodium ion batteries and potassium ion batteries, which is significant for designing long cycle life rechargeable batteries.

and TFSI − ) intercalation, DIBs and RDIBs deliver a high working voltage and consequently a considerable energy density. However, they normally possess unsatisfactory power density because of the sluggish dynamics of large anion intercalation or alloying. Capacitive materials based on surface adsorption or shallow redox reactions are capable of providing a much higher power density. [13][14][15][16] Therefore, replacing intercalation or alloy-type electrodes with at least one adsorption-type material is regarded as an effective way to break through the trade-off of power and energy density. [17] Although the intercalation of anions can bring high voltage, it also results in some adverse issues. The reaction in high voltage holds out harsh requirements to the electrolyte, that is, high voltage may lead to decomposition of the electrolyte. As a consequence, it is needed to develop a kind of cathode that can work at a lower voltage. However, in order to ensure high energy density, it is necessary to increase the specific capacity of the cathode materials. As to the anode, the conversion reactions between metallic Li and lithium halides have been demonstrated to show high capacity and good reversibility with low voltage. By using such conversion reactions, several kinds of halide ion batteries have been developed, including chloride ion batteries, in our recent work. [18][19][20][21] If two electrodes based on adsorption and conversion mechanism can be coupled in one DIB, it would be expectable to construct a rechargeable battery with simultaneously high energy density and power density.Herein, mesoporous vanadium-doped anatase (VTO) synthesized by hydrothermal method and lithium metal is used as cathode and anode, along with a non-lithium electrolyte to assemble an RDIB, respectively. The charge storage of the cathode is based on adsorption/desorption of electrolyte cations, whereas a conversion reaction happens on the anode side, which is totally different from the existing (R)DIBs (Figure 1). The VTO/Li RDIB shows a high capacity of 123.8 mAh g −1 at 200 mA g −1 after 500 cycles. More significantly, it provides a high power density of 1532 W kg −1 along with a considerable energy density of 214 Wh kg −1 at 1 A g −1 . The effective coupling of adsorption and conversion reaction mechanism induces an optimization of the power/energy density of DIBs, providing a new design strategy for high-performance energy storage systems.As one kind of promising energy storage device, dual-ion batteries (DIBs) have attracted extensive attention because of their high voltage, environmental friendliness, and low cost. However, they generally suffer from low power density resulting from sluggish kinetic of electrolyte anion intercalation. In this work, a new strategy to break through the trade-off of power density and energy density in DIBs is proposed. A vanadium-doped anatase is synthesized by the hydrothermal method and used as the cathode of DIB (employing Li as the anode). During the charging/discharging process, the organic ca...