Stress accumulation in Ni-rich layered oxide cathodes:Origin,impact,and resolution

LiNi_(x)Co_(y)Mn_(z)O_(2)(NCM,x+y+z=1)is one of the most promising cathode candidates for high energy density lithium-ion batteries(LIBs).Due to the potential in enhancing energy density and cyclic life of LIBs,Ni-rich layered NCM(NCM,x≥0.6)have garnered significant research attention.However,improved specific capacity lead to severer expansion and shrinkage of layered lattice,accelerating the stress generation and accumulation even microcracks formation in NCM materials.The microcracks can promote the electrolyte permeation and decomposition,which can consequently reduce cyclic stabilities.Therefore,it is significant to provide an in-depth insight into the origin and impacts of stress accumulation,and the available modification strategies for the future development of NCM materials.In this review,we will first summarize the origin of stress accumulation in NCM materials.Next,we discuss the impact of stress accumulation.The electrolyte permeation along microcracks can enhance the extent of side reaction at the interface,trigger phase transformation and consequential capacity fading.To cushion the impact of stress accumulation,we will review five main strategies.Finally,concise perspectives to reduce stress accumulation and enhance particle strength in further works will be presented.

Stable and realistic crack pattern generation using a cracking node method

This paper presents a method for simulating surface crack patterns appearing in ceramic glaze, glass, wood and mud. It uses a physically and heuristically combined method to model this type of crack pattern. A stress field is defined heuristically over the triangle mesh of an object. Then, a first-order quasi-static cracking node method （CNM） is used to model deformation. A novel combined stress and energy combined crack criterion is employed to address crack initiation and propagation separately according to physics. Meanwhile, a highest-stress-first rule is applied in crack initiation, and a breadth-first rule is applied in crack propagation. Finally, a local stress relaxation step is employed to evolve the stress field and avoid shattering artifacts. Other related issues are also discussed, such as the elimination of quadra- ture sub-cells, the prevention of parallel cracks and spurious crack procession. Using this method, a variety of crack patterns observed in the real world can be reproduced by changing a set of parameters. Consequently, our method is robust because the computational mesh is independent of dynamic cracks and has no sliver elements. We evaluate the realism of our results by comparing them with photographs of realworld examples. Further, we demonstrate the controllability of our method by varying different parameters.