| With the development of modern science and technology, high-energy lithium-ion batteries(LIBs) have played a crucial role in the development of consumer electronics, electric vehicles, and grid-scale stationary energy storage. As expected, there has been a growing demand for LIBs withimproved electrochemical performance with regard to higher energy density, longer cycle life and greater safety. Because of their effects on practical applications and safety issues, the energy density(per weight or volume) and cycle life, the major focus of recent battery research, are the most important factors considered for next-generation high-performance LIBs. Currently, graphite is a commonly used anode material in commercial LIBs. However, as the voltage of lithium intercalation into carbon materials closes to lithium metal, some Li-ions may deposit on the surface of the anode leading to lithium dendrite and hence safety concerns. On the other hand, SEI(Solid Electrolyte Interface) Film is essential to form for carbon electrode on the first discharge and charge cycle. What’s more, the SEI film formation may increase the impedance of electrode/electrolyte interface, and doesn’t facilitate the reversible insertion and extraction of Li-ions. Compared with other anode candidates, graphite also lacks a capacity advantage(vs. crystal/amorphous silicon), the rate capability(vs. Li4Ti5O12 spinel), and some other favorable characteristics. Therefore great effort is being devoted to balancing the major requirements of the qualified anode for LIBs.According to various reports, metal-oxide anodes demonstrate attractive prospects after effective modification. Tin dioxide(SnO2), particularly, has been widely investigated for its lithium(Li) storage mechanism of an initial phase conversion reaction followed by a Li-Sn alloying reaction to deliver a theoretical specific capacity of 1494 mAh g-1(SnO2 + 4 Li+ + 4 e- → 2Li2 O + Sn; Sn + 4.4 Li+ + 4.4 e- ? Li4.4Sn). Although the specific capacity is around four times larger than that of a graphite anode, SnO2 electrodes suffer from poor cyclability, with obvious capacity loss after repeated cycling. This capacity loss is mainly caused by the severe particle pulverizations that is triggered by a more than 250% volume change(expansion and shrinkage) upon lithiation/delithiation. Upon long cycles, the pulverization of SnO2 particles is directly associated with a decay in capacity, as uncontrolled volume variations lead to cracking of the electrode, which in turn causes a loss of direct contact with current collector and the electronic conductivity network. This volume change also induces additional growth of SEI layers on the naked SnO2 surface, thereby introducing a corresponding mechanical instability. Moreover, the poor cyclability inevitably results in serious capacity fading upon cycling, especially at high current densities. Thus it is essential to improve the cyclability of SnO2 electrodes by suppressing particle pulverization and volume change, and further enhancing the electronic conductivity network to ensure superior electrochemical performances for use in LIBs.A method to improve the electrochemical performance of SnO2 electrode is to accommodate a large volume change and enhanced electronic conductivity, hence making the Li+ insertion/extraction more sufficiently. For this purpose, the element doped into the SnO2 lattice seems to be an effective way. Recently, cobalt(Co) has been successfully doped into the SnO2 lattice and it has been found that the doped samples exhibit a volume buffering effect(i.e., they accommodate a large volume change) and enhanced electronic conductivity. On the other hand, it iswell established that nitrogen(N)-doped SnO2 exhibitsdesirable enhanced electrical and optical properties, which could be attributed to greatly increased electronic conductivity.Therefore, synergetic doping of Co and N into anSnO2 sample should take advantage of the enhanced volume tolerance as well as good electronic conductivity, which would endow the SnO2 electrode with better Li storage and transport behaviors. However, the electrochemical features of them have been reported rarely.In this paper, we prepared through Cu-N/SnO2、Ni-N/SnO2、Co-N/SnO2和 Fe-N/SnO2 composites through different precursors,a hydrothermal method and further thermally treated underN2 atmosphere, and did a series of work of the study of materials, specific as follows.1. Cu-N/SnO2 composite was synthesized by a simple hydrothermal and further thermally treated underN2 atmosphere which used Cu(NO3)2·3H2O as copper source. A series of characterization of physical properties and electrochemical properties have proved that compared with the pure SnO2 and Cu/SnO2 composite has greatly improved the cycle of material properties and improve the mass specific capacity.2. Ni-N/SnO2 composite was synthesized by a simple hydrothermal and further thermally treated underN2 atmosphere which used NiCl2·6H2O as copper source. A series of characterization of physical properties and electrochemical properties have proved that compared with the pure SnO2 and Ni/Sn O2 composite has greatly improved the cycle of material properties and improve the mass specific capacity.3. Co-N/SnO2 composite was synthesized by a simple hydrothermal and further thermally treated underN2 atmosphere which used Co(NO3)2·6H2O as copper source. A series of characterization of physical properties and electrochemical properties have proved that compared with the pure SnO2 and Co/SnO2 composite has greatly improved the cycle of material properties and improve the mass specific capacity.4. Fe-N/SnO2 composite was synthesized by a simple hydrothermal and further thermally treated underN2 atmosphere which used Fe(NO3)3·9H2O as copper source. A series of characterization of physical properties and electrochemical properties have proved that compared with the pure SnO2 and Fe/SnO2 composite has greatly improved the cycle of material properties and improve the mass specific capacity. |
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