Peng Dai

Lithium (Li) metal anodes have become an important component of the next generation of high energy density batteries. However, the Li metal anode still has problems such as Li dendrite growth and unstable solid electrolyte interface layer. Herein, we present a functional electrolyte additive (PANHF) successfully synthesized from acrylonitrile and hexafluorobutyl methacrylate via a polymerization reaction. With extensive analytical characterization, it is found that the PANHF can improve the reversibility and Coulombic efficiency of the Li deposition/dissolution reaction and prevent the growth of Li dendrites by forming a solid electrolyte interphase rich in organic matter on the outer layer and LiF on the inner layer. The results show that the cycling performance of the Li/Li cell was greatly improved in the electrolyte containing 0.5 wt % PANHF. Specifically, the cycling stability of more than 700 cycles was achieved at a current density of 1.0 mA cm^-2. Moreover, the Li/NCM811 cell with 0.5 wt % PANHF has a higher capacity of 137.7 mA h g^-1 at 1.0 C and a capacity retention of 83.41% after 200 cycles. This work highlights the importance of protecting the Li metal anode with functional bipolymer additives for next-generation Li metal batteries.

Development of high-energy-density rechargeable battery systems not only needs advanced qualitative characterizations for mechanism exploration but also requires accurate quantification technology to quantitatively elucidate products and fairly assess numerous modification strategies. Herein, as a reliable quantification technology, titration mass spectroscopy (TMS) is developed to accurately quantify O-related anionic redox reactions (Li-O₂ battery and nickel-cobalt-manganese (NCM)/Li-rich cathodes), parasitic carbonate deposition and decomposition (derived from air-exposure degradation and electrolyte oxidation), and dead Li⁰ formation (Li-metal battery and over-discharged graphite anode). TMS technology can harvest key information on products (e.g., quantification of oxidized lattice oxygen and solid electrolyte interphase (SEI)/cathode electrolyte interphase (CEI) components) and guide corresponding design strategy by enhancing understanding of the mechanism (e.g., clearly distinguish the catalytic target of highly oxidative Ni⁴⁺ on the NCM cathode). Not limited as a rigid quantification tool for widely known products/mechanisms, TMS technology has been demonstrated as a powerful and versatile tool for the investigations of advanced batteries.

Sodium ion batteries (SIBs), as an alternative and promising energy storage system, have attracted considerable attention due to the abundant reserves and low cost of sodium. However, it remains a great challenge to achieve high capacity and rate capability required for practical applications. Herein, hollow octahedral Co₃Se₄ particles encapsulated in reduced graphene oxide (Co₃Se₄@rGO) were designed and synthesized and exhibited excellent electrochemical performances as anodes of SIBs, especially rate capability. Sodiation/desodiation processes and involved mechanisms were investigated by using in situ TEM and in situ XRD. During sodiation, a crystalline Na₂Se layer with numerous amorphous fine Co nanoparticles dispersed on it was observed to appear on the surface of the original Co₃Se₄@rGO particles, and the movable Co-Na₂Se composites further migrated to the rGO network with high electron/ion dual conductivity, resulting in ultrafast sodium storage kinetics and remarkable rate performance of the Co₃Se₄@rGO anode evidenced by delivering a discharge capacity of 229.3 mAh g^-1 at a large current density of 50 A g^-1. Our findings reveal the fundamental mechanism behind the enhanced performance of the Co₃Se₄@rGO anode and offer valuable insights into the rational design of electrode materials for high-performance SIBs.

Development of high-performance cathode materials is one of the key challenges in the practical application of sodium-ion batteries. Among all the cathode materials, layered sodium transition-metal oxides are particularly attractive. However, undesired phase transitions are often reported and have detrimental effects on the structure stability and electrochemical performance. Cu substitution of zinc in the P2-type Na_0.6Mn_0.7Ni_0.15Zn_0.15-xCu_xO₂ (x = 0, 0.075, and 0.15) composites was investigated in this study for mitigating the biphase transition and enhancing the electrochemical performance of sodium-ion batteries. The coupling effect of Zn and Cu enables an excellent capacity retention of 96.4% of the initial discharge capacity after 150 cycles at 0.1 C in the Na/Na_0.6Mn_0.7Ni_0.15Zn_0.075Cu_0.075O₂ cell. The biphase transition that occurred in the high voltage range has been significantly suppressed after the incorporation of Cu in Na_0.6Mn_0.7Ni_0.15Zn_0.15O₂, which was confirmed by in situ X-ray diffraction studies. Moreover, the substitution of the inert element Zn with electrochemically active Cu leads to the suppression of anionic redox and the occurrence of Cu^2+/3+ redox reaction, and the electrolyte decomposition is impeded after the introduction of electrochemically active Cu in the Na_0.6Mn_0.7Ni_0.15Zn_0.15-xCu_xO₂ composite cathode. The enhanced electrochemical performance in the Na_0.6Mn_0.7Ni_0.15Zn_0.075Cu_0.075O₂ electrode can be ascribed to the coexistence of Zn and Cu and alleviated volumetric change as well as suppressed electrode/electrolyte side reaction after Cu substitution.

The Li–O₂ battery should operate effectively/safely in an open O₂ environment for practical applications, but not trapped in sealed/closed atmosphere. However, the typical use of volatile and flammable electrolyte restricts Li–O₂ battery to be able to be running in open O₂ environment. We report herein, for the first time, a highly electrochemical reversible Li–O₂ battery operated in an open O₂ environment, i.e., under the condition of keeping O₂ flowing continuously based on a nonvolatile and nonflammable sulfolane (TMS) solvent. The electrochemical irreversibility of Li₂O₂/O₂ conversion and incompatibility between Li metal anodes and electrolyte have been addressed via dissolving LiNO₃ in concentrated TMS electrolyte. The tuned electrolyte not only enables a stable solid electrolyte interphase (SEI) with conformal inorganic components (including LiF, LiN_xO_y, and Li₂O) that promotes a uniform Li electro-plating/stripping process but also results in a low charge overpotential, a stable discharge terminal plateau, and reversible O₂ generation of the Li–O₂ battery conducted in an open O₂ environment.