Fabrication of porous lithium titanate self-supporting anode for high performance lithium-ion capacitor

Lithium titanate has unique "zero-strain" characteristics, which makes it promising for rapid energy storage lithium-ion capacitors. However, extremely low electronic conductivity and lithium ion diffusion coefficient severely limit its performance at high rate. Herein, we have constructed in situ clusters of porous lithium titanate nanoparticles on self-supporting carbon nanotube film by combining iron oxide hard template method and F127 soft template method. Due to the nano-structured particle size and the penetrating lithium ion transmission channel, a greatly improved lithium ion diffusion coefficient has been achieved, which brings significantly better electrochemical performance than dense lithium titanate. By assembling with a durable graphene foam cathode, a lithium-ion capacitor with an energy density of up to 101.8 Wh kg-1 was realized(at a power density of 436.1 W kg-1). And its capacitance retention reaches 84.8% after 5000 cycles. With such an alluring result, our work presents a novel lithium-ion capacitor system with practical application prospects.

Carbon-coated lithium titanate: effect of carbon precursor addition processes on the electrochemical performance

In this paper,two carbon-coated lithium titanate(LTO-C1 and LTO-C2)composites were synthesized using the ball-milling-assisted calcination method with different carbon precursor addition processes.The physical and electrochemical properties of the as-synthesized negative electrode materials were characterized to investigate the effects of two carbon-coated LTO synthesis processes on the electrochemical performance of LTO.The results show that the LTO-C2 synthesized by using Li2CO3 and TiO2 as the raw materials and sucrose as the carbon source in a one-pot method has less polarization during lithium insertion and extraction,minimal charge transfer impedance value and the best electrochemical performance among all samples.At the current density of 300 mA·h·g^(-1),the LTO-C2 composite delivers a charge capacity of 126.9 mA·h·g^(-1),and the reversible capacity after 300 cycles exceeds 121.3 mA·h·g^(-1) in the voltage range of 1.0–3.0 V.Furthermore,the electrochemical impedance spectra show that LTO-C2 has higher electronic conductivity and lithium diffusion coefficient,which indicates the advantages in electrode kinetics over LTO and LTO-C1.The results clarify the best electrochemical properties of the carbon-coated LTO-C2 composite prepared by the one-pot method.

Synergy of a hierarchical porous morphology and anionic defects of nanosized Li_(4)Ti_(5)O_(12) toward a high-rate and large-capacity lithium-ion battery

Exploring electrode materials with a high volumetric energy density and high rate capability remains of a great challenge for nanosized-Li_(4)Ti_(5)O_(12)(LTO)batteries.Here,hierarchical porous Ti^(3+)-C-N-Br co-doped LTO(LTOCPB-CC)is synthesized using carboxyl-grafted nanocarbon(CC)and cetylpyridinium bromide(CPB)as combined structure-directing agents.Ti^(4+)-O-CPB/Li^(+)-CC is designed as a new molecular chelate,in which CPB and CC promote the uniform mixing of Li^(+)and Ti^(4+)and control the morphology of TiO_(2) and the final product.The defects(oxygen vacancies and ion dopants)formed during the annealing process increase the electron/hole concentration and reduce the band gap,both of which enhance the n-type electron modification of LTO.As-prepared LTOCPB-CC has a large specific surface area and high tap density,as well as a high electronic conductivity(2.84×10^(-4) S cm^(-1))and ionic conductivity(3.82×10^(-12)cm^(2) s^(-1)),which are responsible for its excellent rate capability(157.7 mA h g^(-1) at 20 C)and stable long-term cycling performance(0.008% fade per cycle after 1000 cycles at 20 C).

Self-supported hierarchical porous Li_(4)Ti_(5)O_(12)/carbon arrays for boosted lithium ion storage

The development of fast rechargeable lithium ion batteries(LIBs)is highly dependent on the innovation of advanced high-power electrode materials.In this work,for the first time,we report a sacrificial NiO arrays template method for controllable synthesis of self-supported hierarchical porous Li_(4)Ti_(5)O_(12)/C(LTO/C)nanoflakes arrays,for use as fast rechargeable anodes for LIBs.The ultrathin(2-3 nm)carbon layer was uniformly coated on the LTO forming arrays architecture.The hierarchical porous LTO/C nanoflakes consisted of primary cross-linked nanoparticles of 50-100 nm and showed large porosity.Because of the enhanced electrical conductivity and accelerated ion transfer channels,the well-designed binderfree porous LTO/C nanoflakes arrays exhibited notable high-rate lithium ion storage performance with smaller polarization,better electrochemical reactivity,higher specific capacity(157 mAh g^(-1) at the current density of 20C)and improved long-term cycling life(96.2% after 6000 cycles at 20C),superior to the unmodified porous LTO arrays counterpart(126 mAh g^(-1) at 20C and 88.0%after 6000 cycles at 20C).Our work provides a new template for the construction of high-performance high-rate electrodes for electrochemical energy storage.

Surface-Engineered Li4Ti5O12 Nanostructures for High-Power Li-Ion Batteries

Materials with high-power charge–discharge capabilities are of interest to overcome the power limitations of conventional Li-ion batteries.In this study,a unique solvothermal synthesis of Li4Ti5O12 nanoparticles is proposed by using an off-stoichiometric precursor ratio.A Li-deficient off-stoichiometry leads to the coexistence of phaseseparated crystalline nanoparticles of Li4Ti5O12 and TiO2 exhibiting reasonable high-rate performances.However,after the solvothermal process,an extended aging of the hydrolyzed solution leads to the formation of a Li4Ti5O12 nanoplate-like structure with a self-assembled disordered surface layer without crystalline TiO2.The Li4Ti5O12 nanoplates with the disordered surface layer deliver ultrahighrate performances for both charging and discharging in the range of 50–300C and reversible capacities of 156 and 113 mAh g−1 at these two rates,respectively.Furthermore,the electrode exhibits an ultrahigh-charging-rate capability up to 1200C(60 mAh g−1;discharge limited to 100C).Unlike previously reported high-rate half cells,we demonstrate a high-power Li-ion battery by coupling Li4Ti5O12 with a high-rate LiMn2O4 cathode.The full cell exhibits ultrafast charging/discharging for 140 and 12 s while retaining 97 and 66% of the anode theoretical capacity,respectively.Room-(25℃),low-(−10℃),and high-(55℃)temperature cycling data show the wide temperature operation range of the cell at a high rate of 100C.

Investigation on process mechanism of a novel energy-saving synthesis for high performance Li_(4)Ti_(5)O_(12) anode material

Li_(4)Ti_(5)O_(12)(LTO) anode material demonstrates superior cycling performance due to its stable spinel structure and high lithiation/de-lithiation potential.Herein,a novel energy-saving solid-phase synthesis route for LTO has been successfully designed,employing the cheap industrial intermediate product of metatitanic acid (HTO) as titanium source.Through the in-situ Fourier transform infrared spectroscopy (FTIR)and ex-situ X-ray diffraction (XRD),it is revealed for the first time that the amorphous crystal structure of HTO is more conducive for the Li+insertion,making it possible to prepare LTO at a relatively lower sintering temperature.Utilizing the dehydration carbonization reaction between glucose and sulfuric acid,an ingenious strategy of glucose pre-coating is adopted to avoid the generation of Li_(2)SO_(4) impurity caused by the residual sulfuric acid on the surface of HTO,which meanwhile enhances the conductivity and inhibits the particle growth of LTO.The obtained ALTO@C anode material consequently exhibits excellent electrochemical performance that 132.0 m Ah g^(-1)is remained even at 20 C,and ultra low decay rate of 0.015% per cycle is achieved during 1000 cycles at 2 C.Remarkably,LiCoO_(2)//ALTO@C full cell delivers conspicuous low-temperature property (130.7 m Ah g^(-1)at 0.5 C and almost no attenuation after 300 cycles under-20℃).

Terminal sulfur atoms formation via defect engineering strategy to promote the conversion of lithium polysulfides

The defect engineering shows great potential in boosting the conversion of lithium polysulfides intermediates for high energy density lithium-sulfur batteries(LSBs),yet the catalytic mechanisms remain unclear.Herein,the oxygen-defective Li_(4)Ti_(5)O_(12)-xhollow microspheres uniformly encapsulated by N-doped carbon layer(OD-LTO@NC)is delicately designed as an intrinsically polar inorganic sulfur host for the research on the catalytic mechanism.Theoretical simulations have demonstrated that the existence of oxygen deficiencies enhances the adsorption capability of spinel Li_(4)Ti_(5)O_(12)towards soluble lithium polysulfides.Some-S-S-bonds of the Li2S6on the defective Li_(4)Ti_(5)O_(12)surface are fractured by the strong adsorption force,which allows the inert bridging sulfur atoms to be converted into the susceptible terminal sulfur atoms,and reduces the activation energy of the polysulfide conversion in some degree.In addition,with the N-doped carbon layer,secondary hollow microspheres architecture built with primary ultrathin nanosheets provide a large amount of void space and active sites for sulfur storage,adsorption and conversion.The as-designed sulfur host exhibits a remarkable rate capability of 547 m Ah g^(-1)at 4C(1 C=1675 m A g^(-1))and an outstanding long-term cyclability(519 m Ah g^(-1)after 1000 cycles at 3 C).Besides,a high specific capacity of 832 m Ah g^(-1)is delivered even after 100 cycles under a high sulfur mass loading of 3.2 mg cm^(-2),indicating its superior electrochemical performances.This work not only provides a strong proof for the application of oxygen defect in the adsorption and catalytic conversion of lithium polysulfides,but offers a promising avenue to achieve high performance LSBs with the material design concept of incorporating oxygen-deficient spinel structure with hierarchical hollow frameworks.

Preparation and characterization of Li_(4)Ti_(5)O_(12) synthesized using hydrogen titanate nanowire for hybrid super capacitor

The electrical characteristics of hybrid super capacitor were evaluated by synthesizing LTO(Li_(4)Ti_(5)O_(12))using TiO_(2) having a hydrogen titanate nanowire form.Preparation of the hydrogen titanate nanowire was implemented by using TiO_(2) having size of 60 nm and NaOH,and performing synthesis at 70℃for 6 h with a sonochemical method.LTO compound was synthesized at 150℃for 36 h and at 180℃for 36 h respectively by using the hydrogen titanate nanowire and LiOH·H2O as starting materials with a hydrothermal method.The final LTO compound was synthesized at 700℃for 6 h using a solid-state method.As a result of manufacturing the hybrid super capacitor using LTO synthesized at 180℃for 36 h with the hydrothermal method,a capacity of 198 mA·h/g has been achieved compared to a theoretical capacity of 172 mA·h/g of existing LTO,and thus,the capacity has been increased by about 13%.Further,such excellent cycle performance has ensured its possibility as a high-capacity capacitor.

Ultrahigh lithiation dynamics of Li_(4)Ti_(5)O_(12)as an anode material with open diffusion channels induced by chemical presodiation

Spinel lithium titanate(Li_(4)Ti_(5)O_(12),LTO),with the merits of safety operation voltage,stable crystal structure,and minor lattice volume changes,becomes an optimal anode material for high-power Li-ion batteries.However,the inherent wide bandgap and low lithiation reactivity of Li_(4)Ti_(5)O_(12)bring about poor conductivity and lithiation dynamics,limiting its further applications.Herein,we design and prepare unique Li_(4)Ti_(5)O_(12)anode materials with extremely low dopant content of Na^(+)utilizing the amorphous precursors.The resultant Li_(4)Na_(0.008-)Ti_(5)O_(12.004)sample(denoted as NLTO-0.008)presents superior rate performances and cycle ability,with a reversible capacity of 149.4 mAh·g^(-1)at the current rate of10.0C.NLTO-0.008 retains the charge capacity of151.3 mAh·g^(-1)with a capacity loss of 0.5%after 1000cycles at the current rate of 1.0C(charge)/10.0C(discharge).The kinetic studies furtherly demonstrate that the lithiation reaction energy and diffusion energy barrier decrease by 28.8%and 30%,respectively.Crystal structure analysis indicates that Na^(+)occupies the 16d Li site and forms distorted LiO_(4)tetrahedron and TiO_(6)octahedron.This lattice distortion forms open diffusion channels,thus enhancing the Li^(+)diffusion dynamics and decreasing the lithiation reaction energy barrier for Li_(4)Ti_(5)O_(12).Therefore,the pre-sodiation strategy may arouse great interest in understanding and developing intercalation-type transitionmetal-based electrode materials in high-power lithium-ion batteries.