Many investigations of anode materials for lithium-ion secondary batteries have been carried out in order to obtain batteries of higher capacity and energy density. Recently, SnO-based glasses, which were prepared by the usual melt quenching technique, have been proposed as a new anode for lithium-ion secondary batteries by Idota et al. 1 It has been reported that the capacity per unit weight was higher than 600 mAh g Ϫ1 and the capacity per unit volume was higher than 2200 mAh cm Ϫ3 , values which are almost double those for carbon materials used as anodes of commercial lithium-ion batteries at present. Thus SnO-based glasses have attracted much interest as high-capacity anode materials for lithium-ion secondary batteries. Courtney and Dahn have pointed out some factors which are responsible for high charge-discharge capacity retention and have drawn conclusions about the electrode reaction mechanism for the glasses in the SnO-B 2 O 3 -P 2 O 5 system. 2 Recently, they have prepared glasses of various compositions in the SnO-B 2 O 3 -P 2 O 5 system and demonstrated the relationship between the aggregation of tin in the glasses caused by the reversible reaction with lithium and the charge-discharge performance of the glasses as an anode. 3 Crystalline compounds including Sn, such as SnO, SnO 2 , and SnSO 4 , have also been found to work as electrode materials. [2][3][4][5][6] On the other hand, much attention has been paid to mechanical milling (MM) using a high-energy ball mill as one of the new preparation techniques of inorganic materials. The MM technique was originally developed as a method to synthesize metallic alloys. 7 In addition, MM is known as a method to form an amorphous phase. 8 Recently, milling has also been used for synthesis of crystalline and amorphous materials in the field of solid-state ionics. Several kinds of solid electrolytes have been synthesized by high-energy ballmilling at room temperature. [9][10][11] If SnO-based amorphous materials can be synthesized by MM, several advantages would be expected; the process is very simple, and the whole process can be performed at room temperature. Furthermore, the samples prepared by MM are directly used as electrode materials for batteries without pulverizing procedures because they are obtained as fine powders. Such fine powders will improve the contacts at interfaces between the electrolytes and electrodes. The samples prepared by MM are thus expected to show excellent properties as an electrode. In addition, new materials which could not be synthesized by the usual melt quenching method are also expected to be obtained.In the present study we have synthesized amorphous materials in the system SnO-B 2 O 3 -P 2 O 5 by MM of starting oxides at room temperature and investigated the properties as electrode materials. The nominal composition of the samples was selected to be SnB 0.5 P 0.5 O 3 , which exhibited high capacity in the case of SnO-B 2 O 3 -P 2 O 5 glasses prepared by melt quenching. 2 In addition, we have tried to synthesize amorphous ma...
The local structure of electrochemically lithium-inserted SnO-B 2 O 3 glasses was investigated by several spectroscopic techniques to clarify a lithium insertion mechanism into the glasses. 50SnO•50B 2 O 3 ͑mol %͒ glass showed two plateaus around 1.5 and 0.5 V ͑vs. Li ϩ /Li͒ on the lithium insertion process and exhibited a high capacity of 1240 mAh g Ϫ1 in the case of using a conventional liquid electrolyte. On the first plateau ͑1.5 V vs. Li ϩ /Li͒, metallic Sn with small domains was formed and the coordination environment at boron in the glass network was not changed. On the second plateau ͑0.5 V vs. Li ϩ /Li͒, the borate glass network was rearranged by a transformation from tetrahedral BO 4 to trianglar BO 3 boron units, which provides an additional free space compensating an increase in volume followed by a formation of Li-Sn alloy domains. Hence, the larger the fraction of tetrahedral BO 4 unit is in the SnO-B 2 O 3 glasses, the higher the charge-discharge capacities are. The SnO-B 2 O 3 glasses are applicable to all-solid-state lithium rechargeable batteries as anode materials with high capacity.Tin oxide-based glasses and crystals have been studied extensively as anode materials for lithium secondary batteries since the first report by Idota et al. [1][2][3][4][5][6][7][8][9] These anode materials show high specific capacities twice that of carbon materials, which are commercially used as anode materials for lithium-ion secondary batteries.Recently, we reported that the binary system SnO-B 2 O 3 has a wide glass-forming region with 0 р SnO ͑mol %͒ р 75, and these glasses work as an anode material with high capacity using a conventional cell with liquid electrolytes. 10 Charge-discharge capacities depend on the glass composition and are maximized at the composition of 50 mol % SnO. 11 B NMR measurements have revealed that four-coordinated boron in the glass network is maximized at the composition of 50 mol % SnO, 11 suggesting that there is a close relationship between electrochemical capacity and local glass structure.To clarify the origin of the relationship, an investigation of structural changes during electrochemical lithium insertion to the SnO-B 2 O 3 binary glasses is important. Structural studies on electrochemical reaction of lithium with SnO-based glasses by several spectroscopic techniques have been reported for multi-oxide systems such as SnO-B 2 O 3 -P 2 O 5 -Al 2 O 3 . 5,6,8 Those studies for the simple binary system SnO-B 2 O 3 , however, have not been examined in detail.Nowadays, developing all-solid-state lithium rechargeable batteries with high reliability and high safety is desirable to replace the current lithium-ion batteries using liquid electrolytes, which have inherently irresolvable problems of leakage and inflammability. Allsolid-state electrochemical cells consisting of Li-In alloy or In ͑an-ode͒, a superionic oxysulfide glass ͑solid electrolyte͒, and LiCoO 2 ͑cathode͒ have been reported to work as lithium secondary batteries and exhibit excellent cycling properties. 12-15 SnO-ba...
Glasses in the systems of Li2O-SnO-B2O3 and Li2O-SnO-BPO4 were prepared by a melt quenching method [
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