Vilayanur V. Viswanathan∗, Daiwon Choi, Donghai Wang11, Wu Xu, Silas Towne,

Ralph E. Williford, Ji-Guang Zhang, Jun Liu, Zhenguo Yang

3. Experiment

3.1. Electrode synthesis

Nanosized LiFePO4 was synthesized using LiCoOCH3•2H2O(reagent grade, Sigma), FeCO2•2H2O (99%, Aldrich), (NH4)H2PO4(99.999%, Sigma–Aldrich), oleic acid (FCC, FG) and paraffin wax(ASTM D 87, mp. 53–57◦C, Aldrich). (NH4)H2PO4 was ball-milledwith oleic acid for 1 h using high energy planetary ball mill in a stainless steel vial. After paraffin wax was addedand milled for 30 min, iron oxalate was added and milled for 10 min.Finally, Li acetate was added and milled for 10 min. The overallmolar ratio was Li:Fe:P:oleic acid:paraffin = 1:1:1:1:2. The precursor paste was dried in an oven at 110◦C for 30 min byheat-treatment in a mini tube furnace at 500◦C for 8 h under UHP-3%H2/97%Ar gas flow with a temperature ramp rate of 5◦C min−1.After the LiFePO4 was obtained, 10 wt% carbon black was milled ina planetary mill for 4 h (Retsch 100CM) at 400 rpm. TiO2/graphenecomposite (2.5 wt% graphene) was obtained by a self-assemblyapproach following our previous work [18]. Microstructures wereanalyzed by field emission scanning electron microscopy (FESEM) (FEI Nova 600) and high resolution transmission electronmicroscopy (HRTEM).

3.2. Entropy measurement

Entropy data of cathodes, anodes, and complete cells wereobtained by monitoring the change in open circuit voltage as afunction of temperature using ETMS-1000. Several cathode andanode powders were obtained from LICO Technology Corp. Cathodes and anodes were prepared by mixing 85% active material, 10%poly (vinylidene fluoride) (PVDF) binder (Alfa Aesar), and 5% carbonblack (Super P-Li, Timcal) in N-methylpyrrolidone (NMP) (Aldrich),and then cast on Al and Cu foils, respectively. Customer-coatedcathode and anode films obtained from Manufacturer A wereused as received for entropy measurement. To measure entropychanges in cathodes or anodes, they were assembled in a Type-2325coin cell in a vacuum glove box with a 0.75 mm-thick, Li-foilanode (Aldrich) and microporous pp pe separator . The electrolyte used was 1 M LiPF6 in a 1:1 mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) (EM Industries),using a coin cell crimper . Complete cells with various cathodes and anodes also were assembledusing a similar procedure to that described above by replacing Limetal with the appropriate anode.