Developing a light weight lithium ion battery – an effective material and electrode design for high performance conversion anodes

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The process of lithium storage by conversion reaction is a subject of intense research in the field of lithium ion batteries as it opens up the possibility of storing more than one mole of lithium per formula unit, leading to very high storage capacities. For instance, lithium storage by conversion reaction in hematite (α-Fe2O3) results in high theoretical capacity of 1005 mAh g−1. Despite numerous attempts, the first cycle reversibility and cyclability achieved in this material have been disappointingly low. To overcome these limitations, we report here an effective “active material-electrode design” incorporating the following features: (i) well-connected active material particles; (ii) adequate active material surface area; (iii) strong particle-current collector adhesion and (iv) superior degree of electrode drying. Incorporating these features in α-Fe2O3 electrodes enhances its overall electrochemical performance. For the first time, a high first cycle reversibility of 90% is reported for lithium storage via conversion reaction in α-Fe2O3. The long term cyclability over 800 cycles demonstrated here is one of highest reported values for this material. Even at high current densities of 5.025 A g−1 (12 mins of charge/discharge), this tailored α-Fe2O3 delivers capacities (446 mAh g−1) in excess of graphite (372 mAh g−1). Most importantly, this anode material shows feasible operation in a full cell containing olivine LiMn0.8Fe0.2PO4 cathode. It is believed that this simple design approach could also be extended to other material systems such as phosphides, sulphides, nitrides and fluorides that store lithium via conversion mechanism.