Boosting the Energy Density of Li||CFx Primary Batteries Using a 1,3-Dimethyl-2-imidazolidinone-Based Electrolyte

Electrolyte Engineering Empowers Li||CFx Batteries to Achieve High Energy Density and Low Self-Discharge at Harsh Conditions

Given its exceptional theoretical energy density (over 2000 Wh kg-1), lithium||carbon fluoride (Li||CFx) battery has garnered global attention. N-methylpyrrolidone (NMP)-based electrolyte is regarded as one promising candidate for tremendously enhancing the energy density of Li||CFx battery, provided self-discharge challenges can be resolved. This study successfully achieves a low self-discharge (LSD) and desirable electrochemical performance in Li||CFx batteries at high temperatures by utilizing NMP as the solvent and incorporating additional ingredients, including vinylene carbonate additive, as well as the dual-salt systems formed by LiBF4 with three different Li salts, namely lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, and LiNO3. The experimental results unfold that the proposed methods not only minimize aluminum current collector corrosion, but also effectively passivate the Li metal anode. Among them, LiNO3 exhibits the most pronounced effect that achieves an energy density of ≈2400 Wh kg-1 at a current density of 10 mA g-1 at 30 °C, nearly 0% capacity-fade rate after 300 h of storage at 60 °C, and the capability to maintain a stable open-circuit voltage over 4000 h. This work provides a distinctive perspective on how to realize both high energy density and LSD rates at high temperature of Li||CFx battery.

Revealing the Mechano-Electrochemical Coupling Behavior and Discharge Mechanism of Fluorinated Carbon Cathodes toward High-Power Lithium Primary Batteries

Unclear reaction mechanisms and unsatisfactory power performance hinder the further development of advanced lithium/fluorinated carbon (Li/CFx ) batteries. Herein, the mechano-electrochemical coupling behavior of a CFx cathode is investigated by in situ monitoring strain/stress using digital image correlation (DIC) techniques, electrochemical methods, and theoretical equations. The DIC monitoring results present the distribution and dynamic evolution of the plane strain and indicate strong dependence toward the material structure and discharge rate. The average plane principal strain of fully discharged 2D fluorinated graphene nanosheets (FGNSs) at 0.5 C is 0.50%, which is only 38.5% that of conventional bulk-structure CFx . Furthermore, the superior structural stability of the FGNSs is demonstrated by the microstructure and component characterization before and after discharge. The plane stress evolution is calculated based on theoretical equations, and the contributions of electrochemical and mechanical factors are examined and discussed. Subsequently, a structure-dependent three-region discharge mechanism for CFx electrodes is proposed from a mechanical perspective. Additionally, the surface deformation of Li/FGNSs pouch cells formed during the discharge process is monitored using in situ DIC. This study reveals the discharge mechanism of Li/CFx batteries and facilitates the design of advanced CFx materials.

Surface Engineering of Fluorinated Graphene Nanosheets Enables Ultrafast Lithium/Sodium/Potassium Primary Batteries

Fluorinated carbon (CFx ) is considered as a promising cathode material for lithium/sodium/potassium primary batteries with superior theoretical energy density. However, achieving high energy and power densities simultaneously remains a considerable challenge due to the strong covalency of the C-F bond in the highly fluorinated CFx . Herein, an efficient surface engineering strategy combining surface defluorination and nitrogen doping enables fluorinated graphene nanosheets (DFG-N) to possess controllable conductive nanolayers and reasonably regulated C-F bonds. The DFG-N delivers an unprecedented dual performance for lithium primary batteries with a power density of 77456 W kg-1 and an energy density of 1067 Wh kg-1 at an ultrafast rate of 50 C, which is the highest level reported to date. The DFG-N also achieves a record power density of 15 256 and 17 881 W kg-1 at 10 C for sodium and potassium primary batteries, respectively. The characterization results and density functional theory calculations demonstrate that the excellent performance of DFG-N is attributed to surface engineering strategies that remarkably improve electronic and ionic conductivity without sacrificing the high fluorine content. This work provides a compelling strategy for developing advanced ultrafast primary batteries that combine ultrahigh energy density and power density.

In Situ Construction of a LiF-Enriched Interfacial Modification Layer for Stable All-Solid-State Batteries

All-solid-state batteries (ASSBs), particularly based on sulfide solid-state electrolytes (SSEs), are expected to meet the requirements of high-energy-density energy storage. However, the unstable interface between the ceramic pellets and lithium (Li) metal can induce unconstrained Li-dendrite growth with safety concerns. Herein, we design a carbon fluoride-silver (CF_x-Ag) composite to modify the SSEs. As lithium fluoride (LiF) nanocrystals can be in situ formed through electrochemical reactions, this LiF-enriched modification layer with high surface energy can more effectively suppress Li dendrite penetration and interfacial reactions between the SSEs and anode. Remarkably, the all-solid-state symmetric cells using a lithium-boron alloy (LiB) anode can stably work to above 2,500 h under 0.5 mA cm^-2 and 2 mAh cm^-2 at 60 °C without shorting. A modified LiB||LiNi_0.6Mn_0.2Co_0.2O₂ (NMC622) full cell also demonstrates an improved capacity retention and high Coulombic efficiency (99.9%) over 500 cycles. This work provides an advanced solid-state interface architecture to address Li-dendrite issues of ASSBs.

Advanced Lithium Primary Batteries: Key Materials, Research Progresses and Challenges

In recent years, with the vigorous development and gradual deployment of new energy vehicles, more attention has been paid to the research on lithium-ion batteries (LIBs). Compared with the booming LIBs, lithium primary batteries (LPBs) own superiority in specific energy and self-discharge rate and are usually applied in special fields such as medical implantation, aerospace, and military. Widespread application in special fields also means more stringent requirements for LPBs in terms of energy density, working temperature range and shelf life. Therefore, how to obtain LPBs with high energy density, wide operational temperature range and long storage life is of great importance in future development. In view of the above, this paper reviews the latest research on LPBs in cathode, anode and electrolyte over the years, and puts forward relevant insights for LPBs, along with the intention to explore avenues for the design of LPBs components in the coming decades and promote further development in this field.