In-situ stress evolution in LixCoO2 cathode during electrochemical cycling
Naba Karan (Brown University), Insun Yoon (Brown University), Siva Nadimpalli (Brown University), Daniel Abraham (Argonne National Laboratory), Allan Bower (Brown University), Pradeep Guduru (Brown University)
Lithium ion batteries: When Chemistry meets Mechanics
Wed 9:00 - 10:30
Salomon 003
There is increasing evidence that electrochemical cycling induced evolution of mechanical stress in the electrode materials actively contributes towards the degradation of lithium-ion battery performance. Mechanical degradation in anode materials due to large volume changes has been demonstrated recently for materials such as silicon, graphite and tin. On the other hand, crystal structure stability as a function of lithium concentration in cathode materials, for example in LixCoO2, is traditionally believed to be the limiting factor for performance degradation of Li ion batteries. The issue of electrochemical cycling induced mechanical structural damage of active cathode materials has not been explored in sufficient detail, although there have been reports of nano-scale crack formation. In the current work, we present stress evolution in LiCoO2 thin film cathodes by monitoring the change in the elastic substrate curvature during electrochemical cycling. LiCoO2 thin films were prepared using solution deposition technique and were structurally characterized using XRD and Raman spectroscopy, which showed predominant presence of well crystalline HT-LiCoO2 phase. In addition, SEM studies revealed the presence of dense microstructural features in the as prepared films. During Li-extraction from LixCoO2, there was almost linear increase in compressive stress up to ~50% Li removal, which is consistent with its lattice parameter evolution during Li removal from in-situ XRD studies, and a maximum compressive stress of ~0.3-0.4 GPa was observed for x~0.5. Upon lithiation there was almost reversible stress evolution in LixCoO2. Similar behavior was also observed for subsequent cycles as well, while limiting the upper charging cut-off voltage to 4.3V. The effect of stress evolution in LiCoO2 during cycling as a function of charging cut-off voltage will be presented and discussed in the light of its crystal structural changes.