Nov_Dec_AMP_Digital

A D V A N C E D M A T E R I A L S & P R O C E S S E S | N O V E M B E R / D E C E M B E R 2 0 1 7 1 8 complex materials processing involved in the synthesis of high quality C-LFP, not yet reflecting the potential low cost of iron and phosphorous. Consequent- ly, as shown by a recent cost analysis of five common cathode materials (LCO, NMC, NCA, LMO, and LFP), they have nearly the same effective energy cost of approximately $55-61/kWh [7] for the cathode material only. At the battery level, the cost must drop by a factor of 3 to 5 to be less than $150/kWh at 1000 cycles to achieve market acceptance. LIBs for automotive applications are now predominantly used in luxury gasoline-powered vehicles for applica- tions such as SLI and idle stop (Porsche and McLaren offer as standard or as an option). Also, they are used in mild hy- brid (Mercedes S400) and full hybrid cars (BMW ActiveHybrid 3/5, Hyund- ai Sonata, Ford C-Max). The market is now introducing or anticipating the ar- rival of several new electric vehicles in- cluding the Tesla 3 (successor of Tesla X), Chevrolet Bolt, and also a few mod- els from other manufacturers including Ford, Hyundai, Toyota, and Volkswa- gen that could potentially use LIBs. This would complement the existing offer- ing of EVs (Tesla, Nissan Leaf), PHEVs (Chevrolet Volt) and HEVs already in production. Automobile manufactur- ers are introducing these EVs to meet more stringent regulations in Califor- nia, which demands that 15% of new vehicles must have “zero” emissions by 2025 as well as plans to ban gasoline and diesel-powered cars by 2050 [8] . C-LFP CATHODE MATERIAL PRODUCTION METHODS Both solid state and hydrother- mal processes synthesize C-LFP at the industrial scale. However, they require multiple, time-consuming steps and/ or costly precursors (Fig. 4). The hydro- thermal process is suitable for power applications because the particles are finer [5] . As electrochemical performance of C-LFP depends on the synthesis method, current research is dedicated to optimizing existing processes and developing new manufacturing tech- nologies [4] . The specific capacity of good quality, commercially produced C-LFP exceeds 150 mAh/g at 0.1 C and has mass fraction between 2-3% car- bon and average primary particle size between 0.5 to 1 µm [9] . The “C” value is a rate of battery discharge/charge where 0.1 C represents a complete discharge/ charge in 10 hours. Melting lithium-, iron-, and phos- phorus-bearing precursors in near stoi- chiometric ratios and casting the LFP that forms around 1000°C requires few- er processing steps and shorter reac- tion time. Moreover, the melt synthesis can consist of less expensive, commod- ity chemicals, ores, battery recycling, or a mixture of such reactants [4,5,10] . Fur- ther, the molten synthesis can operate with coarser reactant particles com- pared to solid state processes. One drawback of this technology is that the synthesized LFP is coarse: The capaci- ty of large particles is lower than that of small particles and their capacity loss with extended charge-discharge cycles is greater [4] . So, comminution steps are required to reduce the synthesized LFP down to submicron particles. Despite this drawback, melt-casting synthe- sis has the potential to produce a good cathode material with low-cost raw Fig. 3 — Price of metals used for common cathode materials in lithium-ion batteries (on a theo- retical kAh basis): LFP = LiFePO 4 ; LMO = LiMn 2 O 4 ; NCA = Li(Ni0.8Co0.15Al0.05)O 2 ; NMC = Li(Ni0.33Mn0.33Co0.33)O 2 ; LCO = LiCoO 2 . Fig. 4 — Types of LFP synthesis methods and their operating conditions (pressure vs. temperature) [14] .