Tuning Li/Ni mixing by reactive coating to boost the stability of cobalt-free Ni-rich cathode

Cobalt-free cathode materials are attractive for their high capacity and low cost,yet they still encounter issues with structural and surface instability.AlPO_(4),in particular,has garnered attention as an effective stabilizer for bulk and surface.However,the impact of interfacial reactions and elemental interdiffusion between AlPO_(4) and LiNi_(0.95)Mn_(0.05)O_(2) upon sintering on the bulk and surface remains elusive.In this study,we demonstrate that during the heat treatment process,AlPO_(4) decomposes,resulting in Al doping into the bulk of the cathode through elemental interdiffusion.Simultaneously,PO_(4)^(3-)reacts with the surface Li of material to form a Li_3PO_(4) coating,inducing lithium deficiency,thereby increasing Li/Ni mixing.The suitable Li/Ni mixing,previously overlooked in AlPO_(4) modification,plays a pivotal role in stabilizing the bulk and surface,exceeding the synergy of Al doping and Li_3PO_(4) coating.The presence of Ni^(2+)ions in the lithium layers contributes to the stabilization of the delithiated structure via a structural pillar effect.Moreover,suitable Li/Ni mixing can stabilize the lattice oxygen and electrode-electrolyte interface by increasing oxygen removal energy and reducing the overlap between the Ni^(3+/4+)e_g and O^(2-)2p orbitals.These findings offer new perspectives for the design of stable cobalt-free cathode materials.

Dependence of lithium metal battery performances on inherent separator porous structure regulation

Boosting of rechargeable lithium metal batteries(LMBs) holds challenges because of lithium dendrites germination and high-reactive surface feature.Separators may experience structure-determined chemical deterioration and worsen Li plating-stripping behaviors when smoothly shifting from lithium-ion batteries(LIBs) to LMBs.This study precisely regulations the crystal structure of β-polypropylene and separator porous construction to investigate the intrinsic porous structure and mechanical properties determined electrochemical performances and cycling durability of LMBs.Crystal structure characterizations,porous structure analyses,and electrochemical cycling tests uncover appropriate annealing thermal stimulation concentrates β-lamellae thickness and enhances lamellae thermal stability by rearranging molecular chain in inferior β-lamellae,maximally homogenizing biaxial tensile deformation and resultant porous constructions.These even pores with high connectivity lower ion migration barriers,alleviate heterogeneous Li^(+) flux dispersion,stabilize reversible Li plating-stripping behaviors,and hinder coursing and branching of Li dendrites,endowing steady cell cycling durability,especially at higher currents due to the highlighted uncontrollable cumulation of dead Li,which offers new insights for the current pursuit of high-power density battery and fast charging technology.The suggested separator structure-chemical nature functions in ensuring cyclic cell stability and builds reliable relationships between separator structure design and practical LMBs applications.

Rolling up MXene sheets into scrolls to promote their anode performance in lithium-ion batteries

Although Ti3 C2 MXene sheets have attracted extensive attention in lithium-ion storage techniques,their restacking makes against and even hinders the Li ions diffusion within them,thereby decreasing the capacity as well as rate performance of conventional MXene anode.Here,for the first time,we roll up the Ti3 C2 Tx sheets into scrolls with unclosed topological structure and the interlayer galleries to alleviate the restacking problem.Thus,Ti3 C2 Tx scrolls as anode materials in lithium-ion batteries(LIBs)have higher capacity and better rate performance than Ti3 C2 Tx sheets.On the bases of these,high-capacity silicon nanoparticles are added during the rolling process to in-situ produce Ti3 C2 Tx/Si composite scrolls.The addition of 10%silicon nanoparticles shows the best overall improvement among capacity,rate capability and cyclic stability for Ti3 C2 Tx scrolls.

Energy Storage Mechanism of Vanadium Nitride via Intercalating Different Atomic Radius for Expanding Interplanar Spacing

As a promising anode material in supercapacitors,vanadium nitride has been widely concerned due to its ultra-high theoretical specific capacitance.However,its routine test capacitance value is still far from the theoretical value and its energy storage mechanism is controversial.In order to solve these two key problems,here we prepare interplanar spacing expanded vanadium nitride materials with different impurity atoms intercalation from two anionic precursors of vanadium-based metal organic frameworks with different functional groups.The obtained vanadium nitride reaches a higher specific capacitance;and further,through ex situ X-Ray diffraction and in situ Raman,the charge storage of vanadium nitride is contributed by two processes:the first benefit is from the K^(+) de/intercalation in the interplanar spacing,and the other one is derived from the redox reaction with OH−by adsorption on surface.Furthermore,both of the first principle calculation and extended experiments support this idea.We believe that such detailed research on the energy storage mechanism can provide a clear idea for the application of metal nitrides in supercapacitors and other energy storage devices.

Synergetic ternary metal oxide nanodots-graphene cathode for high performance zinc energy storage

Zinc-based electrochemistry ene rgy sto rage with high safety and high theoretical capacity is considered to be a competitive candidate to replace lithium-ion batteries.In electrochemical energy storage,multimetal oxide cathode materials can generally provide a wider electrochemical stability window and a higher capacity compared with single metal oxides cathode.Here,a new type of cathode material,MnFe2Co3O8 nanodots/functional graphene sheets,is designed and used for aqueous hybrid Zn-based energy storage.Coupling with a hybrid electrolyte based on zinc sulfate and potassium hydroxide,the asfabricated battery was able to work with a wide electrochemical window of 0.1~1.8 V,showed a high specific capacity of 660 mAh/g,delivered an ultra high energy density of 1135 Wh/kg and a scalable power density of 5754 W/kg(calculated based on the cathode),and displayed a long cycling life of 1000 cycles.These are mainly attributed to the valence charge density distribution in MnFe2Co3O8 nanodots,the good structural strengthening as well as high conductivity of the cathode,and the right electrolyte.Such cathode material also exhibited high electrocatalytic activity for oxygen evolution reaction and thus could be used for constructing a Zn-air battery with an ultrahigh reversible capacity of 9556 mAh/g.

Effect of carboxylic acid groups on the supercapacitive performance of functional carbon frameworks derived from bacterial cellulose

Three-dimensional （3D） carbonaceous materials derived from bacterial cellulose （BC） has been introduced as electrode for supercapacitors in recent. Here, we report a simple strategy for the synthesis of functional carbon frameworks through 2,2,6,6-tetramethylpilperidine l-oxyl radical （TEMPO） mediated oxidation of bacterial cellulose （BC） followed by carbonization. TEMPO-mediated oxidation can efficiently convert the hydroxyls on the surface of BC to carboxylate groups to improve electrochemical activity. Because of its high porosity, good hydrophilicity, rich oxygen groups, and continuous ion transport in-between sheet-like porous network, the TEMPO-oxidized BC delivers a much higher gravimetric capacitance （137.3 Fig） at low annealing temperature of 500℃ than that of pyrolysis BC （31 F/g） at the same annealing temperature. The pyrolysis modified BC obtained at 900℃ shows specific capacitance （160.2Fig）, large current stability and long-term stability （84.2% of its initial capacitance retention after 10,000 cycles）.