Electrolyte irreversible capacity loss

Insolubility in the electrolyte medium to eliminate self-discharge. Interactions with the electrolyte may cause irreversible capacity loss and coulombic efficiency values far from 100 %. 

In practice, Li+ insertion into carbon is not fully reversible during the first cycle there is an irreversible capacity loss, while in the subsequent cycles the coulombic efficiency is close to 100 %. The excess charge (irreversible capacity) consumed in the first cycle is generally ascribed to the formation of a passivating film and to corrosion-like reactions of Li Cf,. The magnitude of this irreversible capacity depends on the kind of carbonaceous material and on the electrolyte composition [143, 144]. 

Sano, A. Maruyama, S., Decreasing the initial irreversible capacity loss by addition of cyclic sulfate as electrolyte additives, J. Power Sources 2009,192, 714-718. 

Usually, with smaller particles, high discharge rate capability of anode is improved but the possible trade-off is experienced in the irreversible capacity loss (ICL) during the first charge/discharge cycle. The ICL on the anode s side is mostly related to the reductive surface reaction between electrolyte and anode s surface, otherwise known as solid-electrolyte interphase (SEl) formation. 

Various approaches have been identified to reduce the extent of electrolyte decomposition and irreversible capacity loss at the carbon negative electrode. By adding additives to PC such as CO, N,0, CO, the self-discharge and cycling behavior of the lithiated carbon electrodes has improved. These additives affect the film properties by decreasing the low-frequency impedance, thus permitting a more rapid Li -ion transport. 

Because analysis of the SiNW electrodes showed that the NWs did not pulverize during cycling, irreversible capacity loss due to lost or disconnected material seems unlikely for low cycle numbers, but it may rather be due to side reactions and SEl formation. For high-surface area materials such as NWs, there may be increased reactivity of the electrode with the electrolyte, which may have implications for long-term cycling, depending on which species are being formed. 

SEl surface films form both on the anode and the cathode and this means that a certain amount of electrolyte is permanently consumed. The irreversible process of SEl formation immobilizes a certain amount of lithium ions within the insoluble salt that constitutes the SEl. Since most LiBs are built as cathode-limited, in an attempt to avoid the lithium metal deposition on the carbonaceous anode at the end of charging, the consumption of the limited lithium ion source during the initial cycles leads to some permanent capacity loss of the cell. Thus, cell energy density and the corresponding cost are compromised. The extent of this irreversible capacity loss depends on the anode-electrolyte-cathode combination chosen. 

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