Accordion-Like Fluorinated Graphite Nanosheets with High Power and Energy Densities for Wide-Temperature, Long Shelf-Life Sodium/Potassium Primary Batteries.

Sodium and potassium are considered to be the most promising anode candidates due to their easy availability, low-cost and similar chemical properties to lithium. Here, novel 3D accordion-like fluorinated graphite nanosheets (FGNSs) are reported as cathodes for sodium primary batteries (SPBs) and potassium primary batteries (PPBs). The FGNSs-x cathode exhibits unprecedented power and energy density due to the impressive 3D structure, high F/C ratio (1.0), and more surface CC bonds (7.14%). The FGNSs-1.0 exhibits very high specific capacities of 831.3 and 834.1 mAh g-1 for SPBs and PPBs, respectively, close to the theoretical capacity. Besides, the maximum energy density of FGNSs-1.0 in SPBs and PPBs are 1960.5 and 2144.6 Wh kg-1 , respectively. The maximum power density for Na/CFx and K/CFx batteries could reach up to 7076.8 and 6227.4 W kg-1 , respectively. The electrochemical performance of FGNSs-1.0 at extreme temperatures (-30 to 100 °C), long storage time (60 days), high mass loading (3.6 mg cm-2 ), and pouch-type cell is also evaluated for the first time. Surprisingly, FGNSs-1.0 has outstanding performance in these projects. Therefore, the new-type Na/CFx and K/CFx primary battery systems developed here have broad application prospects in high-energy applications that require high-power, low-cost, and normal use under extreme conditions.

Large Scale Synthesis of Three-dimensional Hierarchical Porous Framework with High Conductivity and its Application in Lithium Sulfur Battery.

Quick capacity loss due to the polysulfide shuttle effects and poor rate performance caused by low conductivity of sulfur have always been obstacles to the commercial application of lithium sulfur batteries. Herein, an in-situ doped hierarchical porous biochar materials with high electron-ion conductivity and adjustable three-dimensional (3D) macro-meso-micropore is prepared successfully. Due to its unique physical structure, the resulting material has a specific surface area of 2124.9 m2 g-1 and a cumulative pore volume of 1.19 cm3 g-1 . The presence of micropores can effectively physically adsorb polysulfides and mesopores ensure the accessibility of lithium ions and active sites and give the porous carbon material a high specific surface area. The large pores provide channels for the storage of electrolyte and the transmission of ions on the surface of the substrate. The combined effect of these three kinds of pores and the N doping formed in-situ can effectively promote the cycle and rate performance of the battery. Therefore, prepared cathode can still reach a reversible discharge capacity of 616 mAh g-1 at a rate of 5 C. After 400 charge-discharge cycles at 1 C, the reversible capacity is maintained at 510.0 mAh g-1 . This new strategy has provided a new approach to the research and industrial-scale production of adjustable hierarchical porous biochar materials.

Surface-coated AlF3 nanolayers enable polysulfide confinement within biomass-derived nitrogen-doped hierarchical porous carbon microspheres for improved lithium-sulfur batteries.

The electrically insulating and volumetric deformation of sulfur and the shuttle effect of the intermediate lithium polysulfide (LiPSs) have severely hindered the development of lithium-sulfur batteries (LSBs). Herein, a synergistic strategy of hierarchical porous nitrogen-doped carbon microspheres (PNCM) derived from low-cost biomass with surface-coated AlF3 nanolayer as a multifunctional sulfur host (denoted as PNCM@S@AlF3) was developed. The PNCM not only possesses an abundant pore structure, large surface area, and high electrical conductivity but also features an intrinsic N-doped and fluorinated framework, which effectively enhances the physical adsorption and chemical anchoring to LiPSs. In addition, the AlF3 nanolayer protects the open surface of the porous carbon to isolate sulfur species from the electrolyte to reduce irreversible losses while accelerating the redox kinetics of LiPSs through strong polar adsorption and bonding. Hence, the PNCM@S@AlF3 cathode exhibits an initial capacity as high as 1176.2 mAh/g at 0.2C, and the cycling stability and rate capability are superior to that of PNCM@S without AlF3 coating. Impressively, the PNCM@S@AlF3 cathode delivers stable long-term cycling performance at a high rate of 2C, with 95.6% capacity retention after 500 cycles. This work presents a facile, sustainable, and efficient synergistic strategy for developing advanced LSBs.

Ultrafast Li/Fluorinated Graphene Primary Batteries with High Energy Density and Power Density.

Lithium/fluorinated carbon (Li/CFx) primary batteries have essential applications in consumer electronics and medical and high-power military devices. However, their application is limited due to the difficulty in achieving simultaneous high power density and high energy density in the CFx cathode. The tradeoff between conductivity and fluorine content is the decisive factor. Herein, by rational design, 3D porous fluorinated graphene microspheres (FGS-x) with both high conductivity and a high F/C ratio are successfully synthesized for the first time. FGS-x possesses an F/C ratio as high as 1.03, a nanosheet structure with hierarchical pores, abundant C═C bonds, few inactive C-F2 bonds, and electrochemically active C-F bonds. The beneficial features that can increase discharge capacity, shorten the diffusion length for both ions and electrons, enhance the Li+ intercalation kinetics, and accommodate the volume change are demonstrated. The Li/FGS-1.03 coin cell delivers an unprecedented power density of 71,180.9 W/kg at an ultrahigh rate of 50 C (43.25 A/g), coupled with a high energy density of 830.7 Wh/kg. Remarkably, the Li/FGS-1.03 pouch cell exhibits a record cell-level power density of 12,451.2 W/kg at 20 C. The in-depth investigation by the ex situ method on structural evolution at different discharge depths reveals that the excellent performance benefits from the structural stability and the uniform formation of LiF. The FGS-1.03 cathode also has excellent performance in extreme operating temperatures (0 to 100 °C) and high active material mass loading (4.3 mg/cm2). These results indicate that the engineered fluorinated graphene developed here has great potential in applications requiring both high power density and high energy density.

Enhancement Effects of Co Doping on Interfacial Properties of Sn Electrode-Collector: A First-Principles Study.

The Co doping effects on the interfacial strength of Sn electrode-collector interface for lithium-ion batteries are investigated by using first-principles calculations. The results demonstrate that by forming strong chemical bonds with interfacial Sn, Li, and Cu atoms, Co doping in the interface region can enhance interfacial strengths and stabilities during lithiation. With doping, the highest strengths of Sn/Cu (1.74 J m-2) and LiSn/Cu (1.73 J m-2) interfaces are 9.4 and 17.7% higher than those of the corresponding interface systems before doping. Besides, Co doping can reduce interface charge accumulation and offset the decreasing interfacial strength during lithiation. Furthermore, the interfacial strength and electronic stability increase with rising Co content, whereas the increasing formation heat may result in thermodynamic instability. On the basis of the change of formation heat with Co content, an optimal Co doping content has been provided.