Lithium Metal-Copper Vanadium Oxide Battery with a Block Copolymer Electrolyte

Abstract

Lithium (Li) batteries comprising multivalent positive active materials such as copper vanadium oxide have high theoretical capacity. These batteries with a conventional liquid electrolyte exhibit limited cycle life because of copper dissolution into the electrolyte. We report here on the characterization of solid-state Li metal batteries with a positive electrode based on α-Cu 6.9 V 6 O 18.9 (α-CuVO 3 ). We replaced the liquid electrolyte by a nanostructured solid block copolymer electrolyte comprising of a mixture of polystyreneb-poly(ethylene oxide) (SEO) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt. In situ X-ray diffraction was used to follow the Li insertion/de-insertion mechanism into the α-CuVO 3 host material and its reversibility. In situ X-ray scattering revealed that the multistep electrochemical reactions involved are similar in the presence of liquid or solid electrolyte. The capacity fade of the solid-state batteries is less rapid than that of α-CuVO 3 -Li metal batteries with a conventional liquid electrolyte. Hard X-ray microtomography revealed that upon cycling, voids and Cu-rich agglomerates were formed at the interface between the Li metal and the SEO electrolyte. The void volume and the volume occupied by the Cu-rich agglomerates were independent of C-rate and cycle number. There is considerable interest in copper vanadium oxide (CuVO) positive electrodes for rechargeable lithium (Li) batteries. In principle, this material can exhibit high capacity due to multistep electrochemical reactions with Li + ions. In pioneering work, Yamaki and coworkers reported on reversible Li insertion and removal in CuVO compounds.1-3 They showed that a battery comprising a Li metal negative electrode, β-Cu 2 V 2 O 7 positive electrode, and a conventional liquid electrolyte (a mixture of LiClO 4 in propylene carbonate and dimethoxyethane) could be cycled 100 times at 0.5 mA/cm 2 , with an average delivered capacity of 260 mAh/g. The battery failed abruptly due to a short which was attributed to the deposition of Cu metal on the Li electrode. These studies spark considerable interest in CuVO electrodes. [4][5][6][7][8][9][10][11][12][13][14][15][16][17] In a more recent study, Morcrette et al. showed reversible insertion of 6 Li into Cu 2.33 V 4 O 11 through a reversible Cu extrusion-insertion process.18 During the discharge step, the Li + ions enter the host material and the copper ions are pushed to the material edges where they are reduced, forming Cu metal dendrites. During the charge step, Cu metal is oxidized, producing copper ions that re-enter the host material. This original study opened a new class of CuVO materials. 19-21However, for practical applications, battery failure due to dissolution of Cu into the liquid electrolyte and subsequent plating on the Li electrode needs to be addressed.The potential to use poly(ethylene oxide) (PEO) as an electrolyte in Li batteries was demonstrated by Fenton et al. 22 and Armand et al. 23,24 While most of the studies on PEO-based electrolytes emplo...

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