Opportunities for near zero volt storage of lithium ion batteries
There are inherent safety risks associated with inactive lithium ion batteries leading to greater restrictions and regulations on shipping and inactive storage. Maintaining all cells of a lithium ion battery at near zero voltage with an applied fixed load is one promising approach which can lessen (and potentially eliminate) the risk of a lithium ion battery entering thermal runaway when in an inactive state. However, in a conventional lithium ion cell, a near zero cell voltage can be damaging if the anode electrochemical potential increases to greater than the potential where dissolution of the copper current collector occurs (i.e. ∼3.1 V vs. Li/Li+ at room temperature). Past approaches to yield lithium ion cells that are tolerant to a near zero volt state of charge will be reviewed and their anticipated tradeoffs discussed. Additionally, the present work introduces a novel method to prevent the anode potential from increasing to greater than ∼3.1 V vs. Li/Li+ during near zero volt storage by modifying the amount of reversible lithium in a conventional cell using a pre-lithiated anode. Specifically, LiCoO2/MCMB pouch cells fabricated with a pre-lithiated anode maintained 99% of their original capacity after three, 3 day and three, 7 day storage periods at near zero volts under fixed load. A LiCoO2/MCMB pouch cell fabricated with a pre-lithiated anode also maintained its original discharge performance after three, 3 day storage periods under fixed load at 45 °C. Thus, modifying the amount of reversible lithium in a cell with anode pre-lithiation is a promising concept to achieve lithium ion cells with high tolerance to near zero volt storage without modification to typical cell construction parameters or use of unconventional materials.