• PDF / 668,430 Bytes
• 9 Pages / 584.957 x 782.986 pts Page_size
• 94 Downloads / 281 Views

DOWNLOAD

REPORT

---

hao Zhang School of Material Science and Engineering, Beihang University, HaiDian District, Beijing 100191, People’s Republic of China

Junlong Wang Composites Research Institute, Weinan Normal University, Weinan 714000, People’s Republic of China (Received 28 August 2014; accepted 10 December 2014)

Two novel series of cathode materials LiFe1 xMxPO4/C (x  0.0040; M 5 Mn, Fe, Co, Ni, Cu, and Zn) composites based on metal phthalocyanines (MPc) and metal tetrasulfophthalocyanines (MPcTs) to modify lithium iron phosphate (LiFePO4) for lithium-ion batteries (LIBs) are in situ prepared by solvothermal and calcination techniques. Structures and morphologies of all the composites are characterized by normal methods. To evaluate the electrochemical performance of the composites, the charge/discharge capabilities, rate performance, cycling stabilities, cyclic voltammetry profiles, and electrochemical impedance spectroscopy plots of the LIBs using them as cathode materials are measured carefully. The results indicate that most of the composites deliver highly improved initial discharge capacity and show remarkable reversibility and cycling stabilities. Especially, composites using MPcTs as additives are more efficient for the improvement of specific capacity, rate capability, reversibility, and cycling stability.

I. INTRODUCTION

It is widely accepted that lithium-ion batteries (LIBs) have played important roles in many applications such as portable devices, electric vehicles, hybrid electric vehicles, and intelligent grids in recent years.1,2 Among a variety of cathode materials for LIBs, lithium iron phosphate (LiFePO4) is one of the most promising candidates and draws considerable attention. Olivinestructured LiFePO4 owns many strong advantages as follows: (a) high theoretical specific capacity (170 mA h g 1); (b) stable discharge voltage platform (3.4 V (vs. Li1/Li)); (c) relatively high tap density; (d) highly excellent thermal and cycling stability; (e) nontoxicity, harmless, safety, and environmental friendliness; and (f) abundant raw material resources and low cost.2–4 Nevertheless, its intrinsic weak points (poor electronic conductivity and ionic diffusivity) create obstacles to the application and development of LiFePO4.5,6 To overcome the demerits, strategies have been put forward by researchers, such as conductive carbon coating, metal doping, and changing the Contributing Editor: Xiaobo Chen Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/jmr.2014.396 J. Mater. Res., Vol. 30, No. 5, Mar 14, 2015

http://journals.cambridge.org

Downloaded: 14 Mar 2015

size and morphology of the active particles.7–15 In particular, conductive carbon coating is a relatively effective way to improve the specific capacity and rate capability since the transport lengths of both electrons and ions would be shortened.16 Various sources of carbon, including carbon aerogel, glucose, multiwalled-carbon nanotubes, ascorbic acid, graphene, graphene oxide, and some organic solve