CoFBAT investigates the use of a mixed niobium/titanium oxide, namely TiNb2O7 (TNO), that retains the safety advantages of the LTO but provides an almost doubled capacity (>280mAh/g).
Lithium and titanium are elements used widely in anodes for batteries, based on high charge and power to weight ratio. Lithium price is between 12 and 2 $/kg depending on source whereas Titanium oxide is cheap, below 2$/kg Niobium additions have been studied in Lithium iron phosphate cells to increase conductivity (Li4Ti5O12 (LTO) is often used for applications that required long cycling life and high safety. Its electrochemical activity is indeed based on the Ti4+/Ti3+ couple that is centered around 1.55V vs. Li+/Li, thus preventing SEI and Li dendrites formation that occurs below 0.8V. LTO, however, only provide 170mAh/g what strongly limits the energy density of the system.
Two partners are involved in TNO processing CEA in material optimisation in terms of doping and Torrecid for industrial up scale.
As a result of CoFBAT, it has been developed a novel doped titanium niobate that achieves a discharge capacity of 250 mAh/gr. The graph shows the initial performance of material produced in laboratory and initial small up-scaling processes by CEA that were used as starting point for up scaling.
Torrecid has scaled up the TNO compositions developed within the CoFBAT project, adjusting the production parameters. The industrial process is shown below, dosification of raw materials, milling for homogenisation, sintering in multiphase thermal steps and final grinding and sieving. Initial laboratory conditions defined by CEA were adjusted to industrial conditions by Torrecid.
Within the processing of powders, different parameters have been optimised since they influence the final morphology and electrochemical behavior. Industrial process requires raw material dosification, milling and homogenisation, thermal treatment, grinding and sieving.
Work focused on matching the quality of CEA powder by tailoring the processing parameters into Industrial feasible process. For instance, starting laboratory conditions like 4 hours used in milling were modified into Industrial conditions, starting from conventional 10 minutes milling to an optimized 90 minutes process.
The flow chart is shown below. Along the process influence of parameters on morphology, XRD pattern and electrochemical behavior were assessed.
Industrial processing required the optimisation of TiO2 to Nb2O5 ratio. Along the project, different ratios were tested characterising the XRD, electrochemical performance.
COFBAT has developed TNO optimising the doping to improve the ICL as can be seen on the figure.
Image shows the change in microstructure of powder processed by dry (S) versus wet (H), that influences the electrochemical behavior.
At the end of the Industrial upscaling Torrecid came up with a powder matching the quality of CEA as can be seen on the graph.
XRD pattern of final doped TNO developed.