Electrochemical Performance of Amorphous and Crystalline Sn2 P 2 O 7 Anodes in Secondary Lithium Batteries

Abstract

In 1994, Fuji Photo Film Co., Ltd., Japan, filed a patent for nonaqueous Li-ion batteries in which tin composite oxides (TCOs) were used as the active anode material. 1 Since then, much attention has been given to the potential of substituting this class of compounds for carbon negative electrodes in Li-ion batteries. Tin oxide composites are attractive because of their high gravimetric and volumetric specific capacities relative to carbon, which enable cells of higher energy densities to be built. 2 It is reported 2 that most tin composite oxides are amorphous and the Sn(II)-O sites are active for lithium insertion. Although some early Li 7 NMR measurements have been rationalised in terms of an intercalation mechanism for charge and discharge reactions, more recent experimental results based on X-ray diffraction (XRD) analyses of the active materials at different stages of charge and discharge are more satisfactorily explained by the alloying mechanism made famous by Dahn and associates. 3,4 The alloying mechanism assumes the formation of a lithia (Li 2 O) matrix mostly during the first charging cycle. This matrix binds the lithium-tin regions together and smoothens the large volume changes associated with alloying and dealloying in reversible charge and discharge reactions.Both pristine and doped tin oxides 2-6 have been investigated as anode materials. All of these materials show reversible capacities higher than 500 mAh/g but large capacity losses in their first cycles. They were synthesized by classical solid state reactions involving two or more components. In this study, we consider amorphous and crystalline Sn 2 P 2 O 7 as intrinsic P-doped tin oxide composites, and investigated their performance as anode materials for Li-ion batteries. We have chosen Sn 2 P 2 O 7 to circumvent the mixing problem inherent in most solid state reactions. We are particularly interested in the effects of crystallinity on the electrochemical performance of Sn 2 P 2 O 7 . ExperimentalMaterials preparation.-Crystalline Sn 2 P 2 O 7 (98%, Aldrich) was used as received. For the preparation of amorphous Sn 2 P 2 O 7 , crystalline Sn 2 P 2 O 7 was pelletized at 2 ϫ 10 6 Pa and fired in flowing nitrogen in a Lindberg/Blue M tube furnace. After 2 h at 900ЊC, the melt was removed from the furnace and immediately quenched in air between two stainless plates at room temperature. The solid thus formed was carefully ground to powder and the above procedure repeated once more using the ground Sn 2 P 2 O 7 powder as the starting material, and eight more hours of heating at 900ЊC.Composition and structure determinations.-Elemental composition was determined by inductively coupled plasma (ICP) spectroscopy on a Perkin Elmer Optima 3000DV, using digestions of the melt-quenched samples in 1:1 (by volume) mixture of HCl/HNO 3 at 60ЊC. The crystal structure of Sn 2 P 2 O 7 was confirmed by XRD, using a Philips PW1710 diffractometer and Cu K␣ X-ray source ( ϭ 1.54 Å). The 2 range was initially set at 10-70Њ, but was subsequently narrowed to 10-42Њ ...

Electrochemical behavior of Ge and GeX2 (X = O, S) glasses: Improved reversibility of the reaction of Li with Ge in a sulfide medium

“…Hence, the reversible anode peaks at ∼0.35 V and cathode peaks at ∼0.15 V in the differential capacity plots for both glasses are related to the lithium insertion and extraction reactions, respectively, associated with alloying and de-alloying of Li-Ge phases. On the other hand, the irreversible sharp cathodic peaks observed on the first cycle curves are associated with the decomposition of the GeX 2 Similar results are also observed in the TCO glasses [28,29].…”

“…This is superior not only to that of GeO 2 glasses (Fig. 5), but also to that previously reported for the TCO glasses [4][5][6]28,29]. Similar to the case of GeO 2 glass, there are no distinctive XRD patterns found during the discharging and charging process of GeS 2 glass.…”

Preparation of lithium ion conducting glasses and glass–ceramics for all-solid-state batteries

“…Sn 0 ) and Li 2 Obased glassy matrix (irreversible process), and the second plateau is due to the formation of Li-Sn alloy domains (Sn 0 ? Li-Sn) (reversible process) [35][36][37].…”

All-solid-state lithium secondary batteries using sulfide-based glass–ceramic electrolytes

“…Tin-oxide-based glasses [19,20] were reported to work as a negative electrode material with high capacity in lithium ion cells. The cell performance of SnO-based glasses exhibited larger reversible capacity than the corresponding crystalline material [21]. We have also developed a series of SnO-based borate, phosphate, and borophosphate glasses [22,23] and found that the capacity of the cells using these active materials depended on the composition of glasses, and was closely related to local structure of the glasses.…”

“…On the basis of the mechanism of electrochemical lithium insertion to SnObased glassy materials [20][21][22], the first plateau on the charge curve of the cell with the 80SnS·20P 2 S 5 electrode in Fig. 4 is probably due to the formation of metallic Sn nanoparticles and Li 2 S P 2 S 5 glassy matrix (irreversible process), and the second plateau is due to the formation of Li Sn alloy domains (reversible process).…”