Battery cell manufacturing comprises numerous steps requiring co‐optimization, making the development process time consuming and expensive. Lithium‐metal batteries with ionic liquid electrolytes are a promising next‐generation technology for applications demanding high specific energy and safety but currently suffer from limited cycle stability. Optimizing the manufacturing process can improve performance, and early cycle life prediction can accelerate this process, reducing cost and time. However, correlating early‐stage behavior with long‐term stability is challenging. Machine learning (ML) can assist in building these correlations, but feature extraction remains a key hurdle. A set of features manually extracted from the first cycle with high correlation with the battery cycle life is presented here. These features are then used as inputs to a ML model based on linear regression. While the dataset contains batteries that have reached end‐of‐life through two different mechanisms, the model can predict the cycle life with an error of 15.3%. The error decreases to 9.6% when the cells are first sorted by end‐of‐life mechanism. This work highlights the importance of the early charge–discharge behavior of lithium‐metal batteries and how this data can be used to inform on the battery cycle life with a view to greatly reducing experimental workload.

Two high-salt-content ionic liquid electrolytes with distinct cationic chemistries were compared. The one with a phosphonium cation showed superior characteristics, particularly in terms of its enhanced capacity when used in lithium metal batteries.

To realize the advantages of high energy density lithium-metal batteries, their cycle life and safety need to be improved to meet practical and commercial demands. External compression has been shown to improve the performance of lithium-metal batteries through suppressing dendrite growth, densifying the lithium deposit, and improving the lithium deposition morphology. Here, we report the behavior of high-capacity Li||LFP pouch cells in pyrrolidinium-based ionic liquid electrolytes at elevated temperature (50 degrees C) under various levels of compression and discuss the compression-related mechanisms that affect the performance and failure of the cells. Using scanning electron microscopy, we observed more uniform and less dendritic Li deposition at high levels of compression. However, cell pressure evolution data shows significant lithium metal creep above 800 kPa, effectively limiting the maximum applicable compression. Reducing the testing temperature to 25 degrees C and maintaining high compression led to suppressed Li creep and extended the cell cycle life by 40%. The adverse effect of lithium creep on the separator is identified as an important mechanism on the pouch cell cycling behavior and is further discussed herein.

High performance Li vertical bar NMC and Li vertical bar LFP cells using ionic liquid-based electrolytes have previously been demonstrated, whereby the choice of commercial polyolefin separator was found to play a determinative role in the lithium metal anode's cycling performance and stability. Here, the relationship between the separator properties and the lithium metal cycling behavior has been explored by considering the role and importance of electrolyte chemistry and its resultant interactions with the separator and electrode surface. In this study, an ionic liquid electrolyte (ILE) based on the bis(fluorosulfonyl)imide (FSI) anion was chosen, namely N-methyl-N-propylpyrrolidinium FSI (C(3)mpyrFSI) with 3.2 mol.kg(-1) LiFSI. An organic:IL hybrid electrolyte consisting of 20:80 DME:IL (with the same respective LiFSI molalities) was also prepared using the same IL. Five separators were investigated, namely Solupor 7P03A, Solupor 5P03A, Celgard 3501, Celgard 3401, and Celgard 2500, and the combinations of electrolyte-separator were characterized ex situ, both before and and after cycling, in a Li vertical bar Li symmetric coin cell. The interaction between the separator and electrolyte and the subsequent impact on the electrolyte transport properties have been characterized using NMR diffusion and electrochemical impedance spectroscopy measurements (MacMullin number). The evolution of the lithium metal morphology was studied using SEM, revealing the degree to which the deposited lithium grows progressively into the separator during cycling. Identifying the key properties of the electrolyte-separator system (e.g., ion transport) and understanding how they can be modified through choice of separator and electrolyte chemistry to improve the lithium metal anode durability is a critical aspect for the future development of durable, high capacity lithium metal batteries.

Long-term cycling studies of high capacity Li-metalllithium iron phosphate (LFP, 3.5 mAh/cm(2)) cells were carried out using two highly concentrated ionic liquid electrolytes (ILEs). Cells incorporating N-propyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide (C(3)mpyrFSI) or triethylmethyl-phosphonium bis(fluorosulfonyl)imide (P1222FSI), with 50 mol % lithium bis(fluorosulfonyl)imide (LiFSI) electrolytes were shown to operate for over 180 cycles at 50 degrees C at a rate of C/2 (1.75 mA/cm(2)). The choice of separator was identified as a critical factor to enable high areal capacity cycling, with the occurrence of cell failure through a short-circuiting mechanism being particularly sensitive to separator characteristics. Several commercial separators were characterized and tested, and their performance was related to membrane properties such as the MacMullin number, pore size, and contact angle. Celgard 3000 series separators were found to support long-term cycling due to their combination of desirable nanoporosity and wettability. The most compatible cell components were assembled into a pouch cell to further demonstrate the feasibility of ILE incorporation into high-capacity lithium metal batteries for commercial purposes.

The commercialization of high-capacity Si electrodes for lithium batteries has stalled due to the inability to overcome the mechanical degradation and electrolyte consumption that occur as a result of the inherent volume expansion upon charging. Using an ionic liquid (IL) electrolyte, trimethylisobutylphosphonium bis(fluorosulfonyl)imide (P1,1,1,i4FSI) containing a high lithium bis(fluorosulfonyl)imide (LiFSI) salt content of 3.2 mol per kg of IL (50 mol %), inexpensive and high-capacity Si electrodes made from a facile and ball-milling process demonstrated outstanding capacity retention of around 3.5 mAh/cm2 after 300 cycles when cycled at current densities of ∼1500 mA/g (C/2.5) at room temperature. Moreover, high-capacity retention was maintained for 60 cycles at elevated temperatures up to 80 °C, where traditional electrolytes are unable to operate. SEM images suggest that the use of this highly concentrated IL electrolyte promotes the formation of a stable surface layer that accommodates the volume ex...