Understanding the failure mechanism towards developing high-voltage single-crystal Ni-rich Co-free cathodes

Benefited from its high process feasibility and controllable costs,binary-metal layered structured LiNi_(0.8)Mn_(0.2)O_(2)(NM)can effectively alleviate the cobalt supply crisis under the surge of global electric vehicles(EVs)sales,which is considered as the most promising nextgeneration cathode material for lithium-ion batteries(LIBs).However,the lack of deep understanding on the failure mechanism of NM has seriously hindered its application,especially under the harsh condition of high-voltage without sacrifices of reversible capacity.Herein,singlecrystal LiNi_(0.8)Mn_(0.2)O_(2) is selected and compared with traditional LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2)(NCM),mainly focusing on the failure mechanism of Cofree cathode and illuminating the significant effect of Co element on the Li/Ni antisite defect and dynamic characteristic.Specifically,the presence of high Li/Ni antisite defect in NM cathode easily results in the extremely dramatic H2/H3 phase transition,which exacerbates the distortion of the lattice,mechanical strain changes and exhibits poor electrochemical performance,especially under the high cutoff voltage.Furthermore,the reaction kinetic of NM is impaired due to the absence of Co element,especially at the single-crystal architecture.Whereas,the negative influence of Li/Ni antisite defect is controllable at low current densities,owing to the attenuated polarization.Notably,Co-free NM can exhibit better safety performance than that of NCM cathode.These findings are beneficial for understanding the fundamental reaction mechanism of single-crystal Ni-rich Co-free cathode materials,providing new insights and great encouragements to design and develop the next generation of LIBs with low-cost and high-safety performances.

Cooperative structure of Li/Ni mixing and stacking faults for achieving high-capacity Co-free Li-rich oxides

Co-free Li-rich layered oxides(LLOs)are emerging as promising cathode materials for Li-ion batteries due to their low cost and high capacity.However,they commonly face severe structural instability and poor electrochemical activity,leading to diminished capacity and voltage performance.Herein,we introduce a Co-free LLO,Li_(1.167)Ni_(0.222)Mn_(0.611)O_(2)(Cf-L1),which features a cooperative structure of Li/Ni mixing and stacking faults.This structure regulates the crystal and electronic structures,resulting in a higher discharge capacity of 300.6 mA h g^(-1)and enhanced rate capability compared to the typical Co-free LLO,Li_(1.2)Ni_(0.2)Mn_(0.6)O_(2)(Cf-Ls).Density functional theory(DFT)indicates that Li/Ni mixing in LLOs leads to increased Li-O-Li configurations and higher anionic redox activities,while stacking faults further optimize the electronic interactions of transition metal(TM)3d and non-bonding O 2p orbitals.Moreover,stacking faults accommodate lattice strain,improving electrochemical reversibility during charge/discharge cycles,as demonstrated by the in situ XRD of Cf-L1 showing less lattice evolution than Cf-Ls.This study offers a structured approach to developing Co-free LLOs with enhanced capacity,voltage,rate capability,and cyclability,significantly impacting the advancement of the next-generation Li-ion batteries.

Modulation of lattice oxygen boosts the electrochemical activity and stability of Co-free Li-rich cathodes

Co-free Li-rich layered oxide cathodes have drawn much attention owing to their low cost and high energy density.Nevertheless,anion oxidation of oxygen leads to oxygen peroxidation during the first charging process,which leads to co-migration of transition metal ions and oxygen vacancies,causing structural instability.In this work,we propose a pre-activation strategy driven by chemical impregnation to modulate the chemical state of surface lattice oxygen,thus regulating the structural and electrochemical properties of the cathodes.In-situ X-ray diffraction confirms that materials based on activated oxygen configuration have higher structural stability.More importantly,this novel efficient strategy endows the cathodes having a lower surface charge transfer barrier and higher Li+transfer kinetics characteristic and ameliorates its inherent issues.The optimized cathode exhibits excellent electrochemical performance:after 300 cycles,high capacity(from 238 m Ah g^(-1)to 193 m Ah g^(-1)at 1 C)and low voltage attenuation(168 mV)are obtained.Overall,this modulated surface lattice oxygen strategy improves the electrochemical activity and structural stability,providing an innovative idea to obtain high-capacity Co-free Li-rich cathodes for next-generation Li-ion batteries.

Effect of B and Fe substitution on structure of AB_3-type Co-free hydrogen storage alloy

A series of hydrogen storage Co-free AB3-type alloys were directly synthesized with vacuum mid-frequency melting method,within which Ni of La0.7Mg0.3Ni3 alloy was substituted by Fe,B and(FeB) alloy,respectively.Alloys were characterized by XRD,EDS and SEM to investigate the effects of B and Fe substitution for Ni on material structure.The content of LaMg2Ni9 phase within La0.7Mg0.3Ni3 alloy reaches 37.9% and that of La0.7Mg0.3Ni2.9(FeB)0.1 alloys reduces to 23.58%.Among all samples,ground particles with different shapes correspond to different phases.The major substitution occurs in LaMg2Ni9 phase.Electrochemical tests indicate that substituted alloys have different electrochemical performance,which is affected by phase structures of alloy.The discharge capacity of La0.7Mg0.3Ni3 alloy reaches 337.3 mA·h/g,but La0.7Mg0.3Ni2.9(FeB)0.1 alloy gets better high rate discharge(HRD) performance at the discharge rate of 500 mA/g with a high HRD value of 73.19%.

Design of high-performance and sustainable Co-free Ni-rich cathodes for next-generation lithium-ion batteries

Great attention has been given to high-performance and inexpensive lithiumion batteries(LIBs)in response to the ever-increasing demand for the explosive growth of electric vehicles(EVs).High-performance and low-cost Co-freeNi-rich layered cathodes are considered one of the most favorable candidates for nextgeneration LIBs because the current supply chain of EVs relies heavily on scarce and expensive Co.Herein,we review the recent research progress on Co-free Nirich layered cathodes,emphasizing on analyzing the necessity of replacing Co and the popular improvment methods.The current advancements in the design strategies of Co-free Ni-rich layered cathodes are summarized in detail.Despite considerable improvements achieved so far,the main technical challenges contributing to the deterioration of Co-free Ni-rich cathodes such as detrimental phase transitions,crack formation,and severe interfacial side reactions,are difficult to resolve by a single technique.The cooperation of multiple modification strategies is expected to accelerate the industrialization of Co-free Ni-rich layered cathodes,and the corresponding synergistic mechanisms urgently need to be studied.More effects will be aroused to explore high-performance Co-free Ni-rich layered cathodes to promote the sustainable development of LIBs.

A double-layer covered architecture with spinel phase induced by LiPP for Co-free Li-rich cathode with high-rate performance and long lifespan

Co-free Li-rich Mn-based layered oxides are promising candidates for next-generation lithium-ion batteries(LIBs)due to their high specific capacity,high voltage,low cost.However,their commercialization is hindered by limited cycle life and poor rate performance.Herein,an in-situ simple and low-cost strategy with a nanoscale double-layer architecture of lithium polyphosphate(LiPP)and spinel phase covered on top of the bulk layered phase,is developed for Li_(1.2)Mn_(0.6)Ni_(0.2)O_(2)(LMNO)using Li^(+)-conductor LiPP(denoted as LMNO@S-LiPP).With such a double-layer covered architecture,the half-cell of LMNO@S-LiPP delivers an extremely high capacity of 202.5 mAh·g^(−1)at 1 A·g^(−1)and retains 85.3%of the initial capacity after 300 cycles,so far,the best highrate electrochemical performance of all the previously reported LMNOs.The energy density of the full-cell assembled with commercial graphite reaches 620.9 Wh·kg^(−1)(based on total weight of active materials in cathode and anode).Mechanism studies indicate that the superior electrochemical performance of LMNO@S-LiPP is originated from such a nanoscale double-layer covered architecture,which accelerates Li-ion diffusion,restrains oxygen release,inhibits interfacial side reactions,suppresses structural degradation during cycling.Moreover,this strategy is applicable for other high-energy-density cathodes,such as LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2),Li_(1.2)Ni_(0.13)Co_(0.13)Mn_(0.54)O_(2),LiCoO_(2).Hence,this work presents a simple,cost-effective,scalable strategy for the development of high-performance cathode materials.

Co-free/Co-poor high-Ni cathode for high energy,stable and low-cost lithium-ion batteries

Advanced cathode materials have been considered as the key to significantly improve the energy density of lithium-ion batteries(LIBs).High-Ni layer-structured cathodes,especially with Ni atomic content above 0.9(LiN1_(x)M_(1-x)O_(2),x≥0.9),exhibit high capacity to be commercially available in electric vehicles(EVs).However,the intrinsic structure instability of high-Ni materials and the negative impacts severely restrict their further applic ation.In addition,Co has various effective efforts to stabilize the layered structure.Nevertheless,due to the high cost of Co,it is required to be replaced.Therefore,modification methods on increasing the stability of high-Ni cathode with the reduction of Co content have been widely investigated.In this review,we summarized various effective research progresses and several potential modification strategies of Cofree/Co-poor layered c athodes with Ni content over 0.9.The challenges and development opportunities of high-Ni,Cofree/Co-poor cathodes are further overviewed to meet the future commercial energy demands.

Dual-site lattice co-doping strategy regulated crystal-structure and microstructure for enhanced cycling stability of Co-free Ni-rich layered cathode

Affected by cobalt(Co)supply bottlenecks and high costs,Co-free Ni-rich layered cathodes are considered the most promising option for economical and sustainable development of lithium-ion batteries(LIBs).Low-cost LiNi_(x)Al_(1-x)O_(2)(x≥0.9)cathode are rarely reported due to their chemo-mechanical instabilities and poor cycle life.Herein,we employ a strategy of Mg/W Li/Ni dualsite co-doping LiNi_(0.9)Al_(0.1)O_(2)(named as LNA90)cathodes to enhance cycling stability by modifying the crystal structure and forming a center radially aligned microstructure.The Mg/W co-doped LiNi_(0.9)Al_(0.1)O_(2)cathode(named as LNAMW)exhibits high capacity retention of 94.9%at 1 C and 3.0-4.5 V after 100 cycles with 22.0%increase over the pristine cathode LNA90 and maintains the intact particle morphology.Meanwhile,the cycling performance of LNAMW cathode exceeds that of most reported Ni-rich cathodes(Ni mol%>80%).Our work offers a straightforward,efficient,and scalable strategy for the future design of Cofree Ni-rich cathodes to facilitate the development of economical lithium-ion batteries.

Composition optimization and electrochemical characteristics of Co-free Fe-containing AB_5-type hydrogen storage alloys through uniform design

In order to reduce the cost of ABs-type hydrogen storage alloys, effects of substitution of Ce for La （A side） and Fe, Mn, Al for Ni （B side） on structural and electrochemical properties of （LaCe）;（NiFeMnAl）s alloys were studied systematically. To make component uniform and operation easy, uniform design （UD） method was introduced into the study of composition optimization of Co-free Fe-containing ABs-type alloys for the first time. X-ray diffraction （XRD） results showed that the designed alloys were of single CaCus-type structure phase. The replacement of Fe had a severe effect on electrochemical capacity, and the substitution of Fe and A1 had a synergetic action among the unit cell volume, cycling stability and high rate discharge property. Interestingly, it was found that the hydrogen storage alloys with excessively high plateau pressure showed a tilted line in Nyquist plot instead of the semicircle, and the current decayed rapidly to near zero at the beginning of the step in constant potential step （CPS）, indicating that electrochemical impedance spectra （EIS） and CPS cannot accurately measure the electrochemical kinetics process of the hydrogen storage alloys with excessively high plateau pressure.

Unveiling the impact of residual Li conversion and cation ordering on electrochemical performance of Co-free Ni-rich cathodes

The residual Li and Li^(+)/Ni_(2)+cation mixing play essential roles in the electrochemical properties of Ni-rich cathodes.However,a general relationship between the residual Li conversion,cation mixing,and their effects on the Li^(+)kinetics and structural stability has yet to be established,due to the presence of cobalt in the cathode.Here,we explore the synergistic impact of the residual Li conversion and cation ordering on a Co-free Ni-rich cathode(i.e.,LiNi0.95Mn0.05O_(2)).It discloses that the rate capability is mainly affected by residual Li contents and operating voltage.Specifically,residual Li can be electrochemically converted to cathode electrolyte interphase(CEI)below 4.3 V,thus inducing high interphase resistance,and decomposes to produce CO_(2)-dominated gas at 4.5 V,causing temporary enhancement of Li^(+)diffusivity but severe surface degradation during cycling.Moreover,the cycling performance of Co-free Ni-rich cathode is not only determined by Li^(+)/Ni_(2)+cation-ordered superlattice,which enhances the structural stability as it functions as the pillar to impede lattice collapse at a highly charged state,but also by the robust CEI layers which protect the bulk from electrolyte attack under 4.3 V.These findings promote an in-depth understanding of residual Li conversion and Li^(+)/Ni_(2)+cation ordering on Co-free Ni-rich cathode.

Crack-free single-crystalline Co-free Ni-rich LiNi_(0.95)Mn_(0.05)O_(2) layered cathode

The rapid growth in global electric vehicles(EVs)sales has promoted the development of Co-free,Ni-rich layered cathodes for state-of-the-art high energy-density,inexpensive lithium-ion batteries(LIBs).However,progress in their commercial use has been seriously hampered by exasperating performance deterioration and safety concerns.Herein,a robust single-crystalline,Co-free,Ni-rich LiNi_(0.95)Mn_(0.05)O_(2)(SC-NM95)cathode is successfully designed using a molten salt-assisted method,and it exhibits better structural stability and cycling durability than those of polycrystalline LiNi_(0.95)Mn_(0.05)O_(2) (PC-NM95).Notably,the SC-NM95 cathode achieves a high discharge capacity of 218.2 mAh g^(-1),together with a high energy density of 837.3 Wh kg^(-1) at 0.1 C,mainly due to abundant Ni^(2+)/Ni^(3+) redox.It also presents an outstanding capacity retention(84.4%)after 200 cycles at 1 C,because its integrated single-crystalline structure effectively inhibits particle microcracking and surface phase transformation.In contrast,the PC-NM95 cathode suffers from rapid capacity fading owing to the nucleation and propagation of intergranular microcracking during cycling,facilitating aggravated parasitic reactions and rocksalt phase accumulation.This work provides a fundamental strategy for designing high-performance singlecrystalline,Co-free,Ni-rich cathode materials and also represents an important breakthrough in developing high-safe,low-cost,and high-energy LIBs.

Superb strength and ductility balance of a Co-free medium-entropy alloy with dual heterogeneous structures

In present work,we successfully fabricated a novel Co-free non-equiatomic Ni_(46)Cr_(23)Fe_(23)Al_(4)Ti_(4)mediumentropy alloy with dual heterogeneous structures,i.e.three-levels grain structures and heterogeneous L1;precipitates.Experimental results revealed the dual heterogeneous structures lead to remarkable strength-ductility synergy properties in this Co-free medium-entropy alloy,showing high yield strength and ultimate tensile strength of~1203 MPa and~1633 MPa,respectively,remaining an excellent ductility of~28.7%.Further analyses about strengthening and deformation mechanisms indicated precipitation hardening and hetero-deformation induced hardening contribute the majority strength enhancement,meanwhile deformation-induced hierarchical stacking-faults networks,high density Lomer-Cottrell locks and microstructure features of heterogeneous grains and precipitates substantially facilitate the high work-hardening capacity and excellent tensile ductility.This work not only offers fundamental understanding of the strength and deformation mechanisms of the dual heterogeneous structural material,but also provides useful strength design strategy for low-price high performance high/medium-entropy alloys.

南海水合物及伴生游离气储层封堵改造与水平井降压合采模拟研究

中国南海赋存有丰富的水合物资源,且储层周围或下部往往伴生有大量的游离气。迄今为止,南海已发现的大多数水合物储层泥质含量高,渗透率低,降压开采压降难以有效传递,产能束缚严重,例如神狐海域水合物储层两次试采产能均未达到商业开发标准。因此,将水合物气和伴生游离气联合开采逐渐提上日程。在扩大水合物和伴生气储层泄流面积的同时,进一步寻求高效的增产手段是突破开采产能低的关键。储层封堵改造作为一种提高压降传递的有效手段,能够促进水合物分解和伴生气采收,具有良好的应用前景。故而,本文基于中国南海第一次水合物试采站位地质资料,构建了三维非均质开采模型,重点评估了水平井结合储层封堵改造条件下的两气合采产能,并进一步系统研究了封堵层半径、厚度、渗透率比值以及水平井长度对两气合采产能的影响,分析了合采过程中水合物分解气对总产能的最大贡献率(w)。模拟结果表明,水平井辅以储层封堵能有效提高产能,其中水平井长度、封堵层半径和渗透率比值对合采产能影响依次减弱,水平井长度与封堵层直径两个因素之间存在交互影响。此外,伴生气是两气合采过程中的主要气源,储层封堵后井位布设于游离气层较布设于三相层可进一步提高产能。上述研究认识对于提产增效,推动水合物产业化具有重要的工程指导意义。

核桃壳与联苯共热解过程自由基反应模拟

以核桃壳(WS)为原料,联苯(E230)为含苯环类化合物的模型化合物,采用密度泛函理论(DFT)进行模拟计算,以揭示生物质和含苯环类化合物共热解过程酚类化合物生成机制。基于DFT计算结果,发现在E230热裂解反应中,C—C键的键解离能最小且具有最高活性,表明其具有最高的反应潜力;E230裂解产生的苯自由基与WS(以木质素为例)热解产生的OH·,CH_(3)·及OCH_(3)·等小分子自由基结合,生成苯酚、对甲基苯酚和4-甲基儿茶酚等。

蓝色离子型陶瓷墨水的制备及其发色机理的探究

采用EDTA络合法,以可溶性金属盐作为主要原料,形成的金属络合物作为发色体,可制备出无沉淀、发色稳定的蓝色墨水。研究了不同n(Al)/n(Co)比和不同烧成温度对离子型蓝色墨水呈色的影响。采用X射线衍射仪(XRD)、热重差热分析仪(TG-DTA)、紫外-可见光吸收光谱(UV-vis)、傅里叶红外光谱仪(FT-IR)等手段表征了离子型蓝色墨水。结果表明:当n(Al)/n(Co)为2∶0.65时,色度值为L*=45.64,a*=-0.22,b*=-46.67,样品呈现亮蓝色,呈色最佳。对六组不同n(Al)/n(Co)比配制的墨水进行理化性能的测试,其黏度范围在10~30 mPa·s,表面张力在50~65 mN/m,pH值在7.27~7.76之间,墨水静置5个月后,无沉淀且均一、稳定,符合GB/T38985-2020要求。

自贸试验区设立对产业协同集聚的影响效应——基于制度创新的维度

自贸试验区试点政策以其独有的制度创新基因引领要素集聚,聚焦“制度创新赋能产业发展”,会对区内的产业协同集聚产生影响。结合2008—2018年的地级市面板数据,采用渐进式双重差分法,评估了自贸试验区的设立对产业协同集聚的影响效应。研究发现,自贸试验区的设立能够促使区内产业的协同集聚;机制检验结果显示,自贸试验区能通过对外开放制度创新、财政补贴制度创新、公共服务制度创新促进地区产业协同集聚;税收优惠制度创新机制对地区产业协同集聚的促进作用不显著。自贸试验区促进产业协同集聚的效果对处于不同地理区位、行政等级不同的城市具有区域异质性,自贸试验区对不同类型的生产性服务业同制造业的协同集聚促进效果具有行业异质性;空间溢出视角下,自贸试验区政策实施会对相邻地区和经济水平相似地区的产业协同集聚存在先抑后扬的“U”型影响。

细乳液法合成无溶剂水性聚氨酯

以聚丙二醇(PPG-1000)、4,4-二环己基甲烷二异氰酸酯(HMDI)、二羟甲基丙酸(DMPA)、三乙胺(TEA)、聚四氢呋喃醚二醇(PTMG650)、1,4-丁二醇(BDO)以及液体石蜡(CS)为主要原料,PTMG650为反应型助稳定剂并改变其用量,采用细乳液法合成了一系列无溶剂水性聚氨酯(WPU),并研究了反应型助稳定剂的比例对水性聚氨酯性能的影响。结果表明,随着PTMG650比例的增加,聚氨酯胶膜分子链的柔顺性越来越好;胶膜的拉伸强度从26.7 MPa降低到7.2 MPa,杨氏模量从144.4 MPa降低到19.8 MPa。此外,所有胶膜具有良好的耐热性和耐水性。

无氨体系制备球形氢氧化钴的工艺研究

以氯化钴为原料,氢氧化钠为沉淀剂,采用液相沉淀-喷雾干燥制备了球形氢氧化钴。考察了反应物浓度、合成温度、反应pH值、加料速度和干燥温度等工艺参数对氢氧化钴的一次粒子和二次造粒的影响。确定了最佳的工艺条件为:钴液为90~110 g/L,液碱为70~90 g/L,反应温度为55~65℃,加料时间2 h,终点pH为12~13,干燥温度250℃,浆料固含量为20%,离心喷雾转速为14000 r/min。在此条件下制备了二次球形氢氧化钴。

变来流下翼型动态失速的协同射流控制数值模拟

针对直升机前飞时旋翼在变来流下出现动态失速的问题,发展了基于协同射流的翼型动态失速控制方法。选取NACA0012翼型为研究对象,基于转捩SST湍流模型求解非定常雷诺平均Navier-Stokes方程,开展不同参数下协同射流控制翼型动态失速的数值模拟。研究结果表明,协同射流能够有效抑制变来流条件下的翼型动态失速。在变来流下,射流流道对翼型原始气动特性产生不利影响,功率系数的增长速度快于射流动量系数的增加,协同射流存在具有较好控制效果的最佳工作区间。协同射流通过与主流掺混来加速涡系演化,以抑制动态失速,通过增强弦向气流的动能以克服逆压梯度,从而抑制流动分离和促进流动再附着。在马赫数0.283、减缩频率0.151、前进比0.25的条件下,协同射流使翼型升力提高、阻力下降、负俯仰力矩峰降低、流动再附着提前,翼型气动特性得到明显改善。

煅烧温度对高镍无钴LiNi_(0.90)Mn_(0.10)O_(2)正极材料结构与电化学性能的影响

采用固相法在不同的煅烧温度下(725~825℃)合成了高镍无钴LiNi_(0.90)Mn_(0.10)O_(2)正极材料,并通过结构表征和电化学测试考察了煅烧温度对正极材料的结构和电化学性能的影响。结果表明,煅烧温度会改变材料的晶胞参数,在最佳煅烧温度775℃时所制得的正极材料Li^(+)/Ni^(2+)混排程度最低;该煅烧温度制备的样品首次放电比容量最高,同时倍率性能也表现最佳,并且在循环200圈后仍然保持着最高的放电比容量。