Synergistic effects of transition metal substitution in conversion electrodes for lithium-ion batteries

Abstract

Different solid solutions in the Fe x Co 1Àx C 2 O 4 $2H 2 O system have been prepared in the form of nanoribbons by a reverse micelles method. The orthorhombic crystallographic structure differs from the monoclinic massive products FeC 2 O 4 $2H 2 O and CoC 2 O 4 $2H 2 O. The dehydration process is studied by thermal analysis to prepare the anhydrous solid solution oxysalts, in which the nanoribbonshaped particles are preserved and a porous system is developed. Anhydrous mixed oxalates are used for the first time as high-capacity lithium storage materials with improved rate performance, and display synergistic effects as compared with the end members. Fe 0.75 Co 0.25 C 2 O 4 displays a reversible capacity ca. 600 mA h g À1 at 5C rate with a very good capacity retention after 75 cycles by a hybrid mechanism. The solids display faradaic capacities due to a novel conversion reaction that produces nanodispersed transition metals, which is responsible for the high energy density, and a capacitive response that leads to high power densities in Li-ion batteries. The low temperature synthesis of these materials makes them an inexpensive option for this purpose.

Nickel oxalate dihydrate nanorods attached to reduced graphene oxide sheets as a high-capacity anode for rechargeable lithium batteries

“…This reaction is similar to conversion reactions, but the reaction products are metal and lithium oxalate instead of Li 2 O, which is more noticeable in the case of conversion reactions for metal oxides. 45 Using X-ray absorption and Fourier transform infrared studies, Aragon et al 25 also observed this similarity in the formation of Li 2 C 2 O 4 when lithiated (reduced). Upon charging (oxidation), the relative intensity of the XRD pattern gradually increased and was completely recovered to its state before discharge (Figure 3a).…”

“…24 Tirado's group also suggested a possible mechanism during the first lithiation: MC 2 O 4 +2Li + +2e − → M+Li 2 C 2 O 4 . [25][26][27] By contrast, it is not clear whether the presence of oxalate ions can be solely ascribed to the formation of Li 2 C 2 O 4 because the oxalate ions were present in both unreacted MC 2 O 4 (M: Co) and Li 2 C 2 O 4 . 25 Interestingly, thermal decomposition of metal oxalates as precursors usually leads to the production of metal oxides.…”

“…[25][26][27] By contrast, it is not clear whether the presence of oxalate ions can be solely ascribed to the formation of Li 2 C 2 O 4 because the oxalate ions were present in both unreacted MC 2 O 4 (M: Co) and Li 2 C 2 O 4 . 25 Interestingly, thermal decomposition of metal oxalates as precursors usually leads to the production of metal oxides. However, metal oxalates seem to show better lithium storage abilities than metal oxides, although the reason is not clear.…”

“…Although the capacity of graphite is limited, its electrochemical properties are still superior to other electrode materials in terms of capacity retention and rate capability. Recently, new conversion-type materials were introduced by Tirado's group [24][25][26][27] ; these materials showed intriguing electrochemical performance using metal oxalates MC 2 O 4 (M: Mn, Fe, Co, Ni, Cu, Zn), delivering 700-900 mAh g − 1 in several early cycles. Among these metal oxalates, NiC 2 O 4 delivered the highest capacity.…”

“…However, metal oxalates seem to show better lithium storage abilities than metal oxides, although the reason is not clear. [24][25][26][27][28][29] Enhancement of electrical conductivity is another important concern for electrode materials. Coating using carbonaceous substances has been widely accepted as an effective strategy to achieve better conduction properties and to thereby improve electrochemical properties, such as cycling performance and rate capability.…”