Syntheses,challenges and modifications of single-crystal cathodes for lithium-ion battery

Single-crystal cathodes(SCCs)are promising substitute materials for polycrystal cathodes(PCCs)in lithium-ion batteries(LIBs),because of their unique ordered structure,excellent cycling stability and high safety performance.Cathode materials with layered(LiCoO_(2),LiNi_xCo_yMnzO_(2),LiNi_xCo_yAl_(2)O_(2))and spinel structure(LiMn_(2)O_(4),LiNi_(0.5)Mn_(1.5)O_(4))show a relatively stable electrochemical performance,but still lack of sufficient attention in research field.In this review,we begin with the definition,structural features and electrochemical advantages of SCCs.Common SCCs synthesis methods and the thermodynamic growth mechanism of SCCs with oriented facet exposure are summarized in the following part.Then we introduce the problems and challenges of SCCs faced and the corresponding modification strategies.Finally,the industrialization progress of SCCs is brifly outlined.We intend to tease out the difficulties and advances of SCCs to provide insights for future development of high-performance SCCs for practical LIBs.

A Comparative Investigation of Single Crystal and Polycrystalline Ni-Rich NCMs as Cathodes for Lithium-Ion Batteries

Nickel-rich LiNi_(1-x-y)Co_(x)Mn_(y)O_(2)(NCM,1-x-y≥0.6)is known as a promising cathode material for lithium-ion batteries since its superiority of high voltage and large capacity.However,polycrystalline Ni-rich NCMs suffer from poor cycle stability,limiting its further application.Herein,single crystal and polycrystalline LiNi_(0.84)Co_(0.07)Mn_(0.09)O_(2)cathode materials are compared to figure out the relation of the morphology and the electrochemical storage performance.According to the Li^(+)diffusion coefficient,the lower capacity of single crystal samples is mainly ascribed to the limited Li+diffusion in the large bulk.In situ XRD illustrates that the polycrystalline and single crystal NCMs show a virtually identical manner and magnitude in lattice contraction and expansion during cycling.Also,the electrochemically active surface area(ECSA)measurement is employed in lithium-ion battery study for the first time,and these two cathodes show huge discrepancy in the ECSA after the initial cycle.These results suggest that the single crystal sample exhibits reduced cracking,surface side reaction,and Ni/Li mixing but suffers the lower Li^(+)diffusion kinetics.This work offers a view of how the morphology of Ni-rich NCM effects the electrochemical performance,which is instructive for developing a promising strategy to achieve good rate performance and excellent cycling stability.

Mitigating kinetic hindrance of single-crystal Ni-rich cathodes through morphology modulation,nickel reduction,and lithium vacancy generation achieved by terbium doping

Single crystallization has proven to be effective in enhancing the capacity and stability of Ni-rich LiNi_(1-x-y)Co_(x)Mn_(y)O_(2)(SNCM)cathode materials,particularly at high cut-off voltages.Nevertheless,the synthesis of high-quality single-crystal particles remains challenging because of severe particle agglomeration and irregular morphologies.Moreover,the limited kinetics of solid-phase Li^(+)diffusion pose a significant concern because of the extended diffusion path in large single-crystal particles.To address these challenges,we developed a Tb-doped single-crystal LiNi_(0.83)Co_(0.11)Mn_(0.06)O_(2)(SNCM-Tb)cathode material using a straightforward mixed molten salt sintering process.The Tb-doped Ni-rich single crystals presented a quasi-spherical morphology,which is markedly different from those reported in previous studies.Tb^(4+)oping significantly enhanced the dynamic transport of Li^(+)ions in the layered oxide phase by reducing the Ni valence state and creating Li vacancies.A SNCM-Tb material with 1 at%Tb doping shows a Li^(+)diffusion coefficient up to more than 9 times higher than pristine SNCM in the non-diluted state.In situ X-ray diffraction analysis demonstrated a significantly facilitated H1-H2-H3 phase transition in the SNCM-Tb materials,thereby enhancing their rate capacity and structural stability.SNCM-Tb exhibited a reversible capacity of 186.9 mA h g^(-1)at 5 C,retaining 94.6%capacity after 100 cycles at 0.5 C under a 4,5 V cut-off.Our study elucidates the Tb^(4+)doping mechanisms and proposes a scalable method for enhancing the performance of single-crystal Ni-rich NCM materials.

Towards Single-component Molecular Conductor[Ni(dmit)2]by Charge Disproportionation:2[Ni(dmit)2]^0.5→[Ni(dmit)2]+[Ni(dmit)2]^-

A new method of synthesizing single-component molecular conductor [Ni(dmit)2] by the reaction 2(Me4N)[Ni(dmit)2]2 [Ni(dmit)2] + (Me4N)[Ni(dmit)2] is reported. [Ni(dmit)2] exhibits a semiconductive behavior above 167 K, while from 167 K down to the measuring limit of 60 K, it exhibits metallic conductivity.

COF-based single Li^(+)solid electrolyte accelerates the ion diffusionandrestrains dendritegrowthin quasi-solid-state organic batteries

A solid-state electrolyte(SSE),which is a solid ionic conductor and electroninsulating material,is known to play a crucial role in adapting a lithium metal anode to a high-capacity cathode in a solid-state battery.Among the various SSEs,the single Li-ion conductor has advantages in terms of enhancing the ion conductivity,eliminating interfacial side reactions,and broadening the electrochemical window.Covalent organic frameworks(COFs)are optimal platforms for achieving single Li-ion conduction behavior because of wellordered one-dimensional channels and precise chemical modification features.Herein,we study in depth three types of Li-carboxylate COFs(denoted LiOOC-COFn,n=1,2,and 3)as single Li-ion conducting SSEs.Benefiting from well-ordered directional ion channels,the single Li-ion conductor LiOOC-COF3 shows an exceptional ion conductivity of 1.36×10^(-5) S cm^(-1) at room temperature and a high transference number of 0.91.Moreover,it shows excellent electrochemical performance with long-term cycling,high-capacity output,and no dendrites in the quasi-solid-state organic battery,with the organic small molecule cyclohexanehexone(C_(6)O_(6))as the cathode and the Li metal as the anode,and enables effectively avoiding dissolution of the organic electrode by the liquid electrolyte.

Grain size regulation for balancing cycle performance and rate capability of LiNi_(0.9)Co_(0.055)Mn_(0.045)O_(2) single crystal nickel-rich cathode materials

It is challenging to balance the cyclability and rate capability of single crystal nickel-rich cathode materials(Ni>0.8).Multicomponent oxides by spray pyrolysis shows potential as highly-reactive precursors to synthesize single crystal nickel-rich cathode at lower temperature,yet Ni^(2+)will severely inhibit particle growth when Ni content exceeds 0.9.Herein,lithium nitrate(LiNO_(3))with low melting point and strong oxidation is introduced as collaborate lithium salts for fabrication of well-dispersed submicron and micron single crystal LiNi_(0.9)Co_(0.055)Mn_(0.045)O_(2)(NCM90)cathode without extra unit operation.By changing amount of LiNO_(3),particle size regulation is realized and cation disorder can be diminished.The as-prepared material with optimal content of 4 wt%LiNO_(3)(NCM90-4 LN)displays the most appropriate particle size(1μm)with approximately stoichiometric structure,and presents better kinetics characterization of lithium-ion diffusion(15%higher than NCM90)and good electrochemical performance with specific discharge capacity of 220.6 and 173.8 mAh g^(-1) at 0.1 C and 10 C at room temperature,respectively.This work broadens the conventional research methodology of size regulation for single crystal Ni-rich cathode materials and is indispensable for the development of designing principal of nickel-rich cathode materials for lithium-ion batteries.

SINGLE IONIC CONDUCTI0N OF POLYSILOXANE CONTAINING PROPYLENE CARBONATE GROUP AND LITHIUM POLYMERIC SALTS

The polysiloxane containing propylene carbonate side group and several lithium poly-meric salts were synthesized. The structure were confirmed by IR, NMR and XPS. Theblending systems of polysiloxane containing propylene carbonate group with different lithiumpolymeric salts were studied by ion conductivity XPS and DSC. Different lithium poly-meric salts in the blending system lead to conductivity arranged in the following sequence:poly(lithium ethylenebenzene sulfonate methylsiloxane)>poly(lithium propionate methyl-siloxane)>poly(lithium propylsulfonate methylsiloxane)>poly(lithium styrenesulfonate).In the blending system the best single ion conductivity was close to 10^(-5) Scm^(-1) at roomtemperature. XPS showed that at low lithium salt concentration the conductivity increasedwith the increasing content of lithium salt, in consequence of the increase of free ion andsolvent separated ion pair. At high lithium salt concentration the free ion was absent andthe solvent-separated ion pair functioned as carrier.

Analysis of Acoustic Emission Signals Accompanying Growth of Single Aluminum Crystals： Experimental Results and Theoretical Model of the Cluster

The purpose of the work is to identify the acoustic emission （AE） signal in the melt and from the interphase during the crystal growth and to establish the connection between issue parameters： the number of signal events of frequency and the signal power with the growth conditions of temperature gradient and crystallization rate. Experiments on single crystal growth were carried out using hardware and software system which allows to perform spectral Fourier analysis of AE signals and to simultaneously remove the cooling curve for the entire period of crystallization. On the basis of spectral analysis of AE signals, a theoretical model of clusters in the aluminum melt was designed. The experimental results indicate an uneven abrupt advancement of the interface according to the configuration of each individual cluster.

SINGLE-ION CONDUCTIVITY IN POLY (LITHIUM PROPIONATE METHYL SILOXANE)

Poly(lithium propionate methyl siloxane )as a single-ion carrier source was synthesized. The crosslinked film showed lower lithium ionic conductivity at room temperature (about 10^(-10) S/cm). However,the lithium ionic conductivity was obviously increased by blending with high polar polymers such as polyethylene oxide, poly (methylsiloxane - co- ethylene oxide) and poly (methylsiloxane- g- ethylene oxide). In the blend system a high conductivity of 10^(-7)-10^(-5) Scm^(-1) at room temperature was obtained and the single-ion conductivity was deeply influenced by the content of the poly (lithium propionate methyl siioxane). The dc ionic conductivity of the flexible crosslinked films is more stable over time.

输电线路单导线自由扭转覆冰动态仿真研究

输电线路冰灾长期威胁电网安全稳定运行,结合输电线路实际覆冰情况,建立准确的输电线路覆冰增长模型对电网冰灾防御具有重要意义。但现有的输电线路覆冰增长模型多忽略了输电线路自由扭转覆冰过程。该文基于野外自然环境下输电线路单导线自由扭转覆冰的观测结果,建立了反映导线自由扭转覆冰动态过程的仿真分析模型。在重庆大学雪峰山能源装备安全国家野外科学观测研究站开展GJ50导线自由扭转覆冰实验,将实验结果与数值仿真结果进行对比分析。结果表明:导线扭转角度和单位覆冰质量沿单导线中心点对称分布;仿真获得的导线覆冰形状与实际情况吻合;导线扭转角度和单位覆冰质量仿真值与测量值误差平均值均在10%以内。

锂单离子导电聚合物电解质的制备及界面稳定性

以苯乙烯磺酰(三氟甲基磺酰)亚胺锂(Li STFSI)、聚乙二醇甲醚甲基丙烯酸酯(PEGM)和2,2,3,3-四氟丙基甲基丙烯酸酯(TFMA)[或甲基丙烯酸八氟戊酯(OFMA)、甲基丙烯酸十二氟庚酯(DFMA)]为单体,合成了3种锂单离子导电聚合物电解质,并将其制成了隔膜,组装了CR 2025扣式电池。采用FTIR、SEM、EIS和线性扫描伏安法对隔膜进行了表征,对CR 2025扣式电池进行恒电位间歇滴定法测试。结果表明,合成的电解质膜具有较高的离子电导率(90℃,2.0×10^(-5)S/cm)、较宽的电化学稳定窗口(4.5 V)和高的锂离子迁移数(≈1)。电解质膜拥有较高的锂离子扩散系数(60℃,≥3.7×10^(-9)cm^(2)/s)。经热处理后,电解质膜与锂金属的界面稳定性得到明显提升,这归因于含氟侧链基团在聚合物电解质表面的富集。

单离子导体型聚合物电解质的研究进展

研发一种具有高能量密度、更长循环寿命和更高安全性的固态锂电池,是近几年为下一代电池设定的主要目标之一。传统液态电解质存在易燃、易泄露等缺陷,限制了其在锂离子电池中的应用。聚合物电解质具有更高的安全性能,兼具高可加工性、高柔韧性、低可燃性以及宽电化学窗口等优势,有望替代液态电解质,并在下一代高能量密度储能装置中极具应用潜能。与传统双离子导体聚合物电解质(DICPEs)相比,单离子导体型聚合物电解质(SICPEs)具有高的离子迁移数(tLi+接近1),可有效避免浓差极化的形成,抑制锂枝晶生长。文中总结了近几年SICPEs体系的研究进展,梳理了合成方法、分子结构设计,分析了当前单离子导体体系的主要挑战,并对未来该领域的发展方向进行了展望,为锂离子电池用单离子导体的研究提供技术创新方面的启发。

Highly elastic energy storage device based on intrinsically super-stretchable polymer lithium-ion conductor with high conductivity

Stretchable power sources,especially stretchable lithium-ion batteries(LIBs),have attracted increasing attention due to their enormous prospects for powering flexible/wearable electronics.Despite recent advances,it is still challenging to develop ultra-stretchable LIBs that can withstand large deformation.In particular,stretchable LIBs require an elastic electrolyte as a basic component,while the conductivity of most elastic electrolytes drops sharply during deformation,especially during large deformations.This is why highly stretchable LIBs have not yet been realized until now.As a proof of concept,a super-stretchable LIB with strain up to 1200%is created based on an intrinsically super-stretchable polymer electrolyte as the lithium-ion conductor.The super-stretchable conductive system is constructed by an effective diblock copolymerization strategy via photocuring of vinyl functionalized 2-ureido-4-pyrimidone(VFUpy),an acrylic monomer containing succinonitrile and a lithium salt,achieving high ionic conductivity(3.5×10^(-4)mS cm^(-1)at room temperature(RT))and large deformation(the strain can reach 4560%).The acrylic elastomer containing Li-ion conductive domains can strongly increase the compatibility between the neighboring elastic networks,resulting in high ionic conductivity under ultra-large deformation,while VFUpy increases elasticity modulus(over three times)and electrochemical stability(voltage window reaches 5.3 V)of the prepared polymer conductor.At a strain of up to 1200%,the resulting stretchable LIBs are still sufficient to power LEDs.This study sheds light on the design and development of high-performance intrinsically super-stretchable materials for the advancement of highly elastic energy storage devices for powering flexible/wearable electronics that can endure large deformation.

Single crystal growth and electrochemical studies of garnet-type fast Li-ion conductors

All-solid-state batteries have attracted much attention due to their improved safety and higher energy density as compared to the conventional batteries.Owing to the excellent chemical stability against lithium metal and relatively high ionic conductivity at room-temperature,garnet-type fast lithium ion conductors with three-dimensional lithium ion transport channels are promising solid electrolytes for all-solid-state batteries.In order to better understand the intrinsic lithium-ion transport mechanisms and prevent lithium dendrite formation,it is desired to investigate single-crystal solid electrolytes.In this perspective,we review several methods reported to grow single crystals of garnet-type electrolytes.Pros and cons of different growth methods are discussed.Furthermore,we introduce some case studies on electrochemical properties of garnet-type single crystals.In addition,we provide some perspectives about potential research directions of single-crystal solid electrolytes for all-solid-state batteries.

导电聚合物电解质隔膜PEO/LiPCSI的制备及性能研究

以对苯乙烯磺酸钠为原料,通过酰化、氨解、离子交换和聚合反应制得单离子导体聚[(对苯乙烯磺酰)(氰基)亚胺锂](LiPCSI),以聚氧化乙烯(PEO)为聚合物基质,通过溶液浇铸法制备了导电聚合物电解质隔膜PEO/LiPCSI。采用傅里叶变换红外光谱仪、核磁共振波谱仪对LiPCSI的结构进行分析,采用扫描电子显微镜、热重分析仪和电化学工作站对电解质隔膜性能进行了表征。结果表明,氧锂摩尔比(EO/Li^(+))不同的电解质隔膜均具有良好的热稳定性,其中EO/Li^(+)=10的电解质隔膜电化学性能最优,其离子电导率为2.99×10^(-5)S/cm,锂离子迁移数接近于1(锂离子迁移数tLi^(+)=0.94),电化学稳定窗口达到4.77V。

Single Buffer Using Perovskite-like RE_2Zr_2O_7 Oxides for High Temperature Superconducting Coated Conductors

Single buffer layers of either Gd2Zr2O7 (GZO) or La2Zr2O7 (LZO) with different thickness on highly textured Ni-W tapes were compared with respective to the application of YBa2Cu3O7-δ coated conductors. The superconducting performances are improved as the buffer thickness of GZO or LZO increases up to a critical value, such as 310 and 240 nm, respectively. This suggests that a thin buffer layer is insufficient to prevent the Ni diffusion. If the buffer thickness increases further, the superconducting properties degrade, probably due to changes in the microstructure and degradation of the buffer texture. Comparing with LZO, the texture of GZO is hardly dependent on its thickness, due to smaller mismatch for its lattice with that of Ni-W. For both single buffered coated conductors, the superconducting transition temperatures are around 92 K with a transition width less than 1 K. Inductive measurement reveals that the critical current density (Jc) at 77 K in self-field, reaches 1.2 MA/cm2 and 0.77 MA/cm2 for GZO, and LZO, respectively. This implies that the single buffers of GZO and LZO are comparable to standard buffer architectures such as CeO2/YSZ/Y2O3 or CeO2/LZO, being promising for the process simplification and cost reduction.

高分子固体电解质材料研究进展

高分子固体电解质材料由于具有优良的成膜性和粘弹性等特点 ,近年来得到了很大的发展。本文综述了高分子固体电解质材料的电性能、离子传导特性、提高其性能的途径及近期发展 。

一种基于空心线圈的电流测量新方法

提出了一种基于空心线圈的电流测量新方法,通过在导线周围空间按一定规则布置的空心线圈组来测量电流。分析了单个线圈感应电压与单相导线电流的关系。分别提出了单相和三相电流的测量方法并进行了仿真。制作了实际的空心线圈组,并进行了电流测量实验。对线圈安装过程中可能存在的位置偏差对测量精度的影响进行了仿真分析。仿真和实验结果验证了该方法的正确性。

BP神经网络模型用于单芯电缆导体温度的动态计算

电力电缆导体温度动态计算方法一直是电缆设计、运行管理和电力调度所关注的问题,但用BP神经网络作此研究很少,为此,提出了以电缆运行电流和电缆实时表面温度为基本参量,考虑电缆敷设环境因素,并利用已有的110kV XLPE单芯电缆运行试验数据作为训练学习数据的BP神经网络模型。研究分析结果表明:该BP神经网络模型具有较高的精度,可以用于基于电缆实时表皮温度和运行电流,实时地计算电缆导体温度,且不受电缆本身的物性参数影响,对电力电缆载流量设计、电缆线路负荷优化和电力电缆运行管理以及相关工程实践具有参考意义。

特高压交流单回试验线段雨天电晕损失研究

输电线路电晕损失研究是中国1000kV特高压输变电工程的主要研究内容之一,输电线路电晕损失和诸多气象因素有关,其中降雨率对电晕损失影响非常明显。对特高压交流单回试验线段电晕损失进行监测,并在人工淋雨条件下测量特高压电晕笼导线电晕损失,对2种试验方法测得结果进行等效对比分析,验证了其等效性和试验线段电晕损失监测结果的正确性。当降雨率增大到一定程度后(大雨条件下),电晕损失值增加逐渐趋于饱和。获得了小雨、中雨、大雨条件下中国特高压交流单回输电线路用8×LGJ–500/35分裂导线电晕损失的实测结果,为衡量特高压交流单回输电线路的运行经济性提供了参考依据。