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.

Dynamic stress accumulation model of granite residual soil under cyclic loading based on small-size creep tests

The creep behaviors of granite residual soil with pre-stress of 100 kPa was investigated by a series of small size creep tests. Three different types of strain curves were obtained at different stress levels. Based on creep characteristics of the granite residual soil under different stress levels, a creep model of the granite residual soil was established by rheological theory, and related parameters of the model were determined according to the experimental data at the same time. Further on, based on the established creep model, a theoretical model of dynamic stress accumulation in the granite residual soil under cyclic loading was deduced. It is found that there is a threshold of dynamic stress accumulation in this theoretical model. The dynamic stress accumulation laws of the granite residual soil are different under different cyclic loading stress. Finally, with the dynamic stress accumulation laws in the small-size samples of granite residual soil under different cycle loading studied and the experimental results comparing with the theoretical results, it verifies the validity of the theoretical model.

In situ stress measurement and analysis of the stress accumulation levels in coal mines in the northern Ordos Basin,China

For non-directional drilling cores,selection of samples and the test methods for in situ stress measurements to evaluate the Kaiser effect(KE)were proposed,and the magnitude and direction of the principal stresses were derived from first principles.Based on this approach,the KE for 423 samples in the Burtai and Baode coal mines in the northern Ordos Basin(NOB),China,have been investigated.The results show that the maximum horizontal principal stress(σ_(H)),the minimum horizontal principal stress(σ_(h))and the vertical stress(σ_(v))varied with depth and location,and the values increase with increasing depth.Generally,the horizontal stresses play a leading role.For the main stress regimes in the NOB,σ_(H)>σ_(h)>σ_(v)(Burtai Mine,<172 m;Baode Mine,<170 m)andσ_(H)>σ_(v)>σ_(h)(Burtai Mine,170-800 m;Baode Mine,170-400 m),and theσ_(v)>σ_(H)>σ_(h)stress regimes are mainly distributed in moderately deep to deep coal mines.For rock masses with a depth of 350 m,k((σ_(H)+σ_(h))/2σ_(v))tends to 1,indicating that a deep critical state will gradually emerge.The test results are compared with those for the overcoring(OC)method,the anelastic strain recovery(ASR)method and micro-hydraulic fracturing(HF).The relative errors forσ_(H),σ_(h)andσ_(v)were 14.90%,19.67%,15.47%(Burtai Mine)and 10.74%,22.76%,19.97%(Baode Mine),respectively,and the errors are all within an acceptable range,thus verifying the reliability of the KE method.The dominant orientation for theσ_(H)(Burtai mine,NE-NNE;Baode Mine,NEE)is obtained via paleomagnetic technology,and the data are consistent with those(NE-NEE)of the earthquake focal mechanism solutions for the area.Based on the Byerlee-Anderson theory,a discussion is given on the levels of stress accumulation in the rock mass of the mines.For dry rocks or hydrostatic pressure rocks,the friction coefficients of the faults are low for both locations,and the values are less than the lower limit(0.6)of the strike-slip faults slip,indicating that the stress fractures at a low level around the study areas are lower than the friction limit stress.The stress accumulation levels in the Baode Mine are slightly larger than those in the Burtai Mine.

Influence of complicated faults on the differentiation and accumulation of in-situ stress in deep rock mass

High geostress will become a normality in the deep because in-situ stress rises linearly with depth.The geological structure grows immensely intricate as depth increases.Faults,small fractures,and joint fissures are widely developed.The objective of this paper is to identify geostress anomalies at a variety of locations near faults and to demonstrate their accumulation mechanism.Hydrofracturing tests were conducted in seven deep boreholes.We conducted a test at a drilling depth of over one thousand meters to reveal and quantify the influence of faults on in-situ stresses at the hanging wall,footwall,between faults,end of faults,junction of faults,and far-field of faults.The effect of fault sites and characteristics on the direction and magnitude of stresses has been investigated and compared to test boreholes.The accumulation heterogeneity of stresses near faults was illustrated by a three-dimensional numerical simulation,which is utilized to explain the effect of faults on the accumulation and differentiation of in-situ stress.Due to regional tectonics and faulting,the magnitude,direction,and stress regime are all extremely different.The concentration degree of geostress and direction change will vary with the location of faults near faults,but the magnitude and direction of in-situ stress conform to regional tectonic stress at a distance from the faults.The focal mechanism solution has been verified using historical seismic ground motion vectors.The results demonstrate that the degree of stress differentiation varies according to the fault attribute and its position.Changes in stress differentiation and its ratio from strong to weak occur between faults,intersection,footwall,end of faults,and hanging wall;along with the sequence of orientation is the footwall,between faults,the end of faults,intersection,and hanging wall.This work sheds new light on the fault-induced stress accumulation and orientation shift mechanisms across the entire cycle.

Effects of the February 12,2014 M_S 7.3 Yutian Earthquake on Seismicity of the Northeastern Edge of Qinghai-Tibetan Block

First of all,using the GPS velocity field from campaign GPS measurements implemented by CMONC( C hina Crustal Movement Observation) a nd TEONC( C hina Tectonic Environment Observation Networks) u p to 2013, w e analyzed the background of regional crustal horizontal movement and deformation before the M S7. 3 Yutian,Xinjiang earthquake on February 12,2014. Then,by comparing this to the vertical movement from leveling measurements,we studied the crustal movement deformation and the state of strain accumulation on the northeastern edge of Qinghai-Tibetan block.Finally,we investigated the possible effects on the earthquake activity of the northeastern edge of Tibet from the M S7. 3 Yutian earthquake. The result indicates that,the M S7. 3Yutian earthquake occurred against the background of strong tectonic movement and intensive intracontinental crustal differential movement on the edges of tectonic blocks in western China,and also that it happened in the period of the strong tectonic stress field in Qinghai-Tibetan block and its edges. The sinistral strike-slip and stress transfer of the Yutian M S7. 3 earthquake may accelerate the rupture of fault segments with high strain accumulation at the northeastern edge of Qinghai-Tibetan block( especially in Qilian Mountain fault zone,and border area of Gansu,Qinghai and Sichuan provinces on the south of western Qinling).