Investigation of Copper-Cobalt-Oxides as Model Systems for Composite Interactions in Conversion-Type Electrodes for Lithium-Ion Batteries

Abstract

Different Cu-Co-O mixtures (CCO) with cation ratios from 5:1 to 1:5 were investigated as conversion type electrodes in half cells against lithium counter electrodes. To achieve a nearly homogeneous distribution of the elements on the nanometre scale, the self-combustion method was employed. The electrochemical redox behavior of the single oxides and CCO were characterized with cyclic voltammetry and galvanostatic cycling. These investigations showed different element specific electrochemical characteristics. Copper oxide was more stable with respect to cycling stability, while cobalt oxide had a higher specific capacity. The combination of both elements in ternary CCO leads to an improvement of the specific capacity and the cycling stability compared to the binary metal oxides of only copper and cobalt, respectively. This stabilization effect qualifies CCO as a promising model system to elucidate the underlying mechanisms in such composites with complex interactions between the different metals during conversion and in successive cycling.Lithium ion batteries (LIB), firstly commercialized by Sony Corporation in 1991, 1 are actually the favorite power sources in portable electronic devices like mobile phones or notebooks. 2 Currently applied electrode materials mainly react according to the intercalation mechanism. 3 In this case lithium ions are inserted into stable host structures and are extracted without structure decomposition. Therefore, the possible attainable capacity is limited by the changes, the crystal structure of the host is able to withstand. 4 To overcome this disadvantage 3d transition metal oxides, which follow a displacement or conversion-type mechanism, have recently gained the interest of the scientific community. The advantage over e.g. intercalation materials is the proposed independency from a stable crystal host structure as long as Li can react with a redox active partner. Furthermore, theoretical specific capacities larger than 600 mAh/g can be achieved, since more than one Faraday charge per mole is transferred during the electrochemical reaction. The principle of a conversion reaction with an irreversible structure change can be deduced from equation 1:This electrode type was spotlighted by the works of Tarascon et al. [5][6][7][8] The starting material is converted into an amorphous mixture of metallic clusters embedded in a Li 2 O-matrix. 4 A wide range of possible materials including 3d transition metal oxides, 5,7-11 sulfides 12,13 or hydrides 14 can be used as conversion-type electrodes. The above mentioned advantages are accompanied by limitations like the rather low cycling stability and the large potential difference between charge and discharge. 4 This constraints have to be circumvented before commercial applications might become viable. To improve the cycling stability ternary compounds like CuFe 2 O 4 , 15 NiFe 2 O 4 , 16,17 CoFe 2 O 4 , 16,18 FeCo 2 O 4 19 and CuCo 2 O 4 20were synthesized or assisting compounds like SnO 2 21 were added. The interaction of two or more elem...

An integrated experimental and modeling study of the effect of solid electrolyte interphase formation and Cu dissolution on CuCo 2 O 4 ‐based Li‐ion batteries

“…Considerable effort has been devoted to using conversion materials as prospective anodes in lithium-ion (Li-ion) batteries, due to their high capacity with optimized composition and morphology. [1][2][3] Due to its relatively good capacity, compared to graphite, CuCo 2 O 4 (CCO) is a potential candidate for anode material in Li-ion batteries. 4,5 However, several degradation issues need to be solved to unlock the potential of this material for prolonged battery life.…”

Atomic Layer Deposition of SnO2-Based Composite Anodes for Thin-Film Lithium-Ion Batteries

“…The formed metals during the charging process do not alloy and dealloy with lithium anymore, instead, accompanying the reduction and oxidation. The metallic nanonetwork embedded in a Li 2 O matrix formed after the reaction can improve the overall conductivity of the electrode (Wadewitz et al, 2013;Bruck et al, 2016;Lu et al, 2018). This essential merit can effectively elucidate the pulverization problem caused by volume changes and allow capacity improvement owing to their multiple redox reaction.…”

Atomic resolution observation of conversion-type anode RuO2during the first electrochemical lithiation

“…Despite the effect of the solid electrolyte interphase (SEI), the problems are suggested to be significant volume changes leading to induced mechanical stresses large enough to fracture, which eventually make the system becoming electrically disconnected and possibly inactive. [15][16][17] Meanwhile, the Coulomb efficiency of the first cycle is of critical importance to most anode materials and determines the cycling behavior afterwards. 18,19 Therefore, it is crucial to uncover what exactly happens in the first lithiation.…”