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.

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.

Effect of Drought Stress During Flowering Stage on Starch Accumulation and Starch Synthesis Enzymes in Sorghum Grains

Starch content is a key factor affecting sorghum grain quality. The research of sorghum grain starch accumulation and the related synthesis enzyme activities has great signiifcance for understanding the mechanisms of starch metabolisms. The differences between a high and a low starch content sorghum hybrids （Tieza 17 and Liaoza 11, respectively） in grain starch accumulation and the related synthesis enzyme activities were assessed following imposition of water stress during lfowering stage. The total starch, amylase and amylopectin accumulation all decreased at the mid-late stage of grain iflling under drought stress during lfowering stage. The maximum and mean accumulation rates also decreased. During grain iflling, soluble starch synthase （SSS）, granule-bound starch synthase （GBSS）, starch branching enzyme （SBE）, and starch debranching enzymes （DBE） activities were all affected, though differently. Drought stress reduced starch accumulation in a larger extent for Tieza 17 than Liaoza 11. Drought stress during lfowing stage reduced starch synthesis enzyme activities, thus reducing starch accumulation in grains, and the differences between starch components were also demonstrated under drought stress.

Response of Nitrate Metabolism in Seedlings of Oilseed Rape(Brassica napus L.) to Low Oxygen Stress

In order to understand the response of nitrate metabolism in seedlings of oilseed rape （Brassica napus L.） to low oxygen stress （LOS）, two cultivars were studied at different light, LOS time and exogenous nitrate concentrations under hydroponic stress. Results show that N-uptake and dry matter of rape seedlings were decreased after LOS stress while nitrate accumulation （NA） under LOS was induced by darkness. Nitrate accumulation peaked at 3 d while root activity （RA, deifned as dehydrogenase activity） decreased with prolonged waterlogging exposure. Exogenous nitrate signiifcantly elevated NA and RA. Tungstate （TS） and LOS inhibited nitrate reductase （NR） activity while NR transcription and activity were enhanced by exogenous nitrate. Low oxygen stress stimulated the activity of superoxide dismutase （SOD） and peroxidase （POD） slightly, but inhibited that of catalase （CAT）. B. napus L. Zhongshuang 10 （ZS10）, a LOS tolerant cultivar, displayed smaller decrease upon dry matter under LOS, higher NA in darkness and lower NA in light than B. napus L. Ganlan CC （GAC）, a LOS sensitive variety. ZS10 had lower NA and higher RA after waterlogging and exogenous nitrate treatment, and higher NR activity under TS inhibition than GAC, but the activity of antioxidant enzymes did not change under LOS. The results indicate that nitrate metabolism involved tolerance of rape seedlings to LOS, with lower accumulation and higher reduction of nitrate being related to higher LOS tolerance of rape seedlings exposed to waterlogging.