Enhanced low-temperature performance of slight Mn-substituted LiFePO4/C cathode for lithium ion batteries

Abstract

Low temperature performance of LiFePO 4 /C cathode was remarkably improved by slight Mn-substitution. Electrochemical measurements showed that about 95% of the discharge capacity of LiFe 0.98 Mn 0.02 PO 4 /C cathode at 20°C was obtained at 0°C, compared to 85% of that of LiFePO 4 /C cathode. The LiFe 0.98 Mn 0.02 PO 4 /C sample also presented enhanced rate performance at -20°C with the discharge capacities of 124.4 mA h/g (0.1C), 99.8 mA h/g (1C), 80.7mAh/g (2C) and 70 mA h/g (5C), respectively, while pristine LiFePO 4 /C only delivered capacities of 120.5 mA h/g (0.1C), 90.7 mA h/g (1C), 70.4 mA h/g (2C) and 52.2 mA h/g (5C). Cyclic voltammetry measurements demonstrated an obvious improvement of the lithium insertion-extraction process of the LiFePO 4 /C cathode by slight Mn-substitution. The results of FSEM observation and electrical conductivity measurement indicated that slight Mn-substitution minimized the particle size of LiFe 0.98 Mn 0.02 PO 4 /C and also obviously improved the electrical conductivity of the compound, thus obviously enhances the interface reaction process on the cathode. Lithium ion phosphate has been intensively investigated in recent years as the most promising cathode material for large-scale lithium ion batteries (such as EV and HEV ) due to its low cost, low toxicity, reasonable capacity and good thermal stability [1][2][3][4]. Commercial application of this material has made great progress. It has been successfully used in batteries for laptops, power tools and electric bicycles, etc. However, there are still a number of issues to work out before the batteries are suitable for EV and HEV application, such as high rate capability and low temperature performance. Several effective approaches such as carbon coating on the particle surface [5][6][7][8], minimizing the particle size [9][10][11], and cation substitution [12] have been applied to overcome the high rate problems at room temperature. However, efforts still need to be focused on enhancing low temperature performance of LiFePO 4 cathode. Although many efforts have been made on improving the low *Corresponding author (email: liaoxz@sjtu.edu.cn) temperature performance of lithium ion batteries by developing new low temperature electrolytes [13][14][15], improving the low temperature properties of the electrode materials is also imperative. In our previous work [16], we reported the low temperature performance of LiFePO 4 /C cathode in a quaternary carbonate-based electrolyte. It was found that charge-discharge behavior of LiFePO 4 /C cathode was obviously impeded at low temperature. The increase of chargetransfer resistance and the decrease of lithium ion diffusion capability were the main performance limiting aspects at low temperature. In our present work, we managed to improve the rate capability of LiFePO 4 /C cathode at low temperatures by slight Mn-substitution of Fe-site in LiFePO 4 structure.

Morphology-controllable solvothermal synthesis of nanoscale LiFePO4 in a binary solvent

“…Various synthetic and material modification approaches have been pursued to overcome the ionicand electronictransport limitations of LFP. Among them, conductive agent coating [2-5] and supervalent cation doping [6][7][8] have been widely used for improving the electronic conductivity on the surface and in the bulk of LFP particles, respectively, though the doping effect is still a point of controversy [9,10]. Another common approach to improve the high-rate property of LFP is to use nano-sized particles, which can not only shorten the diffusion length for electrons and Li-ions but can also increase the effective reaction area [11][12][13].…”

Mechanism studies of LiFePO4cathode material: lithiation/delithiation process, electrochemical modification and synthetic reaction

“…It was 60 believed that the dopants replaced metal ions in LiFePO 4 lattice, could enhance the electronic and ionic conductivity. [24] In 2011, Liao's group [155] optimized LiFePO 4 by slight Mn-substitution. The as-obtained LiFe 0.98 Mn 0.02 PO 4 /C delivered 99.8 mAh·g -1 (1C) at -20 o C, which is superior to 90.7 mAh·g -1 for LiFePO 4 /C.…”

Environmental Sustainability Assessment of Typical Cathode Materials of Lithium-Ion Battery Based on Three LCA Approaches

“…Meanwhile, the LiFe 0.98 Mn 0.02 PO 4 /C, as an improved cathode material for LiFePO 4 /C [11], also shows promising development potential. As Zeng [12] confirmed, the electrochemical performance of LiFePO 4 /C was remarkably improved by a slight manganese substitution, creating the general formula LiFe X Mn 1-X PO 4 /C [13]. However, most commercial cathode materials are LiCoO 2 /C, whose actual capacity is 140-155 mAhg −1 , while LiFePO 4 /C or LiFe 0.98 Mn 0.02 PO 4 /C's theoretical capacity is only 170 mAhg −1 , so LIBs urgently need a new cathode model, like FeF 3 (H 2 O) 3 /C [14].…”