Novel materials for negative electrodes in lithium-ion batteries

Carbonaceous materials are currently utilized as negative electrodes in commercial rechargeable Li-ion batteries. However, their low capacity prompted the search for alternative materials of higher capacity and good cycling stability in order to maximize the battery energy density and cycle life.; Lithium alloys have long been considered as alternative negative electrode materials to substitute for the carbonaceous materials currently used in commercial rechargeable Li-ion batteries. However, they suffer from cracking caused by the large volume changes occurring during lithiation and delithiation.; To better understand the alloys failure mechanism, various elements were tested and those that can alloy with lithium electrochemically were identified. Silicon showed extremely high capacity but poor cycle life. To investigate to which extent multiphase materials may improve cycle life, several binary metal-silicides were explored in search for improved cycling stability. Mg ₂Si was the only compound of high capacity but it exhibited poor cycle life.; Both addition of a matrix and decrease in particle size have been demonstrated to improve cycle life. Each effect has been investigated separately. Using tin-based powders of different size oxidized to various extent, we showed an increase in oxygen content, a particle size decrease and the formation of converted Sn-Sb compounds improved cycling stability; The effect of the matrix nature on the electrochemical properties was explored using Zn-based conversion materials. Upon reaction with lithium, ZnO and ZnS electrodes generated LiZn and a Li₂O and Li₂S matrix, respectively. The reversible process was identified as the Li-Zn alloying reaction, as obtained in pure metallic Zn electrodes. ZnO and ZnS failure mechanisms were also similar to metallic Zn. However, ZnS showed improved cycle life; LiZnN has been isolated by way of an electrochemical conversion reaction of Zn₃N₂ with lithium. We showed Zn₃N ₂ reversibly reacts with lithium electrochemically. Zn₃N ₂ converted into LiZn and a matrix of βLi₃N. Upon oxidation, LiZn transformed into metallic Zn, while βLi₃N contributed to the transformation into LiZnN. This process was reversible on subsequent cycles. This was the first identification of a reversible Li₃N conversion mechanism. The formation of LiZnN as the new end member of the electrochemical reaction of Zn₃N₂ with lithium was identified as the cause of the irreversible loss observed during the first cycle. We showed LiZnN, obtained for long mechanomillings, used as starting materials exhibited no irreversible capacity loss in the first cycle and also improved cycling stability; Germanium and copper nitride were found to reversibly react electrochemically with lithium and exhibit good cycling stability. Cu₃N showed complex electrochemistry that involved several processes in parallel. One facet of the reaction with lithium consisted of a reversible metal nitride conversion into a nanocomposite of metallic Cu plus Li₃N similar to what we obs erved with LiZnN. While Ge₃N₄ structural characterization revealed no change upon cycling possibly suggesting an intercalation process may occur upon reaction with Li. The presence of a non-trivial decrease in x-ray diffraction intensity during the first cathodic scan still leaves open the possibility of other reaction mechanism...