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The relentless development and modularization of electronics have urgently required the all-round improvement of performance, flexibility, safety, miniaturization and integration of micro-batteries. However, traditional cell design in stacked geometry fails to meet these comprehensive demands, especially high-temperature performance. Herein, we report the prototype construction of all-solid-state planar lithium ion micro-batteries (LIMBs), with characteristics of superior volumetric energy density, exceptional flexibility, extraordinary high-temperature performance, and outstanding integration of bipolar cells. The planar LIMBs were manufactured based on the interdigital patterns of lithium titanate nanospheres/graphene as anode and lithium iron phosphate microspheres/graphene as cathode, free of polymer binder and separator, working in ionogel electrolyte. The resulting LIMBs deliver ultrahigh volumetric energy density of 125.5 mWh cm−3, ultralong-term cyclability without capacity loss after 3300 times at room temperature, and outstanding rate capability due to the multi-directional Li-ion diffusion mechanism. Furthermore, our micro-batteries present exceptional flexibility without capacity decay under repeated bending, remarkable high-temperature performance up to 1000 cycles operated at 100 °C, superior miniaturization and simplified modularization of constructing intergrated LIMBs that readily control over the output voltage and capacity, all of which can’t be simultaneously achieved by the conventional techniques. Therefore, our planar LIMBs hold tremendous opportunities for future miniaturized and integrated electronics.

The severe lithium polysulfide (LiPS) shuttling and self-discharge behavior of lithium-sulfur (Li-S) batteries remarkably hinder their practical application. The construction of interlayer is an effective strategy to obstruct the diffusion of LiPS. However, the simplex physical block or chemical absorption of monotonous interlayer is difficult to reuse sulfur species, reduce impedance and restrain self-discharge of the Li-S battery simultaneously. In this study, a multicomponent sandwich-type interlayer was integrated by vanadium disulfide and carbon nanotubes composite (VS2/CNT), carbon nanofibers (CNF) substrate and graphene coating layer. The VS2/CNT presented strong affinity towards LiPS and effectively restrained the self-discharge of Li-S batteries. The CNF substrate as supporting framework increased the wettability of electrolyte and reduced the diffusion impedance of lithium ion. The graphene coating layer acting as the second collector effectively recovered the inactivated sulfur species. The multiple components of VS2/CNT adsorbent, CNF substrate and graphene coating layer exhibited favorable synergetic effects to suppress the LiPS shuttling and self-discharge of Li-S batteries. Besides, this interlayer endowed Li-S batteries with boosted redox kinetics and outstanding rate performance. The specific capacities at 0.1, 1 and 10 C were 1525, 834 and 621 mAh g−1, respectively. More importantly, the Li-S batteries with this multicomponent interlayer performed a high residual capacity of 605 mAh g−1 after 1145 cycles at 1 C. Even at a high sulfur loading of 5.6 mg cm−2, the cell still had high capacity of 1150 mAh g−1 and 750 mAh g−1 at 0.1 C and 0.3 C, respectively. The synergetic effects of multicomponent sandwich-type composite interlayer provided a new strategy for ultra-small self-discharge and stable of Li-S batteries.

The rapid development of lithium (Li)-ion and sodium (Na)-ion batteries requires advanced solid electrolytes that possess both favorable electrochemical performance and safety assurance. Herein we report a hierarchical poly (ionic liquid)-based solid electrolyte (HPILSE) for high-safety Li-ion and Na-ion batteries. This hybrid solid electrolyte is fabricated via in situ polymerizing 1,4-bis[3-(2-acryloyloxyethyl)imidazolium-1-yl]butane bis[bis(trifluoromethanesulfonyl)imide] (C1-4TFSI) monomer in 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMITFSI)-based electrolyte which is filled in poly(diallyldimethylammonium) bis(trifluoromethanesulfonyl)imide (PDDATFSI) porous membrane. The well-designed hierarchical structure simultaneously provides the prepared HPILSE with high ionic conductivity (>10 −3 S cm −1 at 25 °C), satisfied electrochemical stability, inherent incombustibility, good mechanical strength and flexibility. More intriguingly, the in situ assembled LiFePO 4 /Li and Na 0.9 [Cu 0.22 Fe 0.30 Mn 0.48 ]O 2 /Na cells using HPILSE exhibit superior cycling performances with high specific capacities. Both the excellent performance of HPILSE and the simple fabricating process of HPILSE-based solid-state cells make it potentially as one of the most promising electrolyte materials for next generation Li-ion and Na-ion batteries.

The high solubility of polysulfides in the electrolyte, together with the resulting poor cycling performance, is one of the main obstacles to the industrial production and use of lithium-sulfur (Li-S) batteries. We have developed a novel hybrid and dense separator coating that greatly improves the cycling and rate performance of the battery. The coating is fabricated by mono-dispersed Li 4 Ti 5 O 12 (LTO) nanospheres uniformly embedded in graphene layers. In this hybrid dense coating, the LTO nanospheres have a high chemical affinity for polysulfides and an excellent ionic conductivity to produce highly efficient ionic conductive channels, while the graphene layers play twin roles as a physical barrier for polysulfides and an upper current collector. The unique hybridization guarantees a very dense coating that does not significantly add the volume of the battery and meanwhile achieves an ideal combination of an effective barrier for polysulfide diffusion with a fast ion transport. For a normal coating, a loose and very thick structure is needed to meet these requirements. Cells using a pure sulfur electrode with the dense coating separator show an ultra-high rate performance (709 mA h g −1 at 2 C and 1408 mA h g −1 at 0.1 C) and an excellent cycling performance (697 mA h g −1 after 500 cycles at 1 C with 85.7% capacity retention). The easy achieving of such excellent performance indicates the possibility of producing an industrially practical Li-S battery.

The ability to suppress the dissolution of lithium polysulfides in liquid electrolyte (LE) is emerging and scientifically challenging, representing an important endeavor toward successful commercialization of lithium–sulfur (Li–S) batteries. In this context, a common and effective strategy to address this challenge is to replace the LE with a gel polymer electrolyte (GPE). However, the limited ionic conductivity of state-of-the-art GPEs and poor electrode/GPE interfaces greatly restrict their implementation. Herein, we report, for the first time, a facile in-situ synthesis of pentaerythritol tetraacrylate (PETEA)-based GPE with an extremely high ionic conductivity (1.13×10−2 S cm−1). Quite intriguingly, even interfaced with a bare sulfur cathode, this GPE rendered the resulting polymer Li–S battery with a low electrode/GPE interfacial resistance, high rate capacity (601.2 mA h g−1 at 1 C) and improved capacity retention (81.9% after 400 cycles at 0.5 C). These remarkable performances can be ascribed to the immobilization of soluble polysulfides imparted by PETEA-based GPE and the construction of a robust integrated GPE/electrode interface. Notably, due to the tight adhesion between the PETEA-based GPE and electrodes, a high-performance flexible polymer Li–S battery was successfully crafted. This work therefore opens up a convenient, low-cost and effective way to substantially enhance the capability of Li–S batteries, a key step toward capitalizing on GPE for high-performance Li–S batteries.

The ability to synthesizing monodisperse Li 4 Ti 5 O 12 (LTO) nanospheres is the key to reducing the irreversible capacity of LTO materials, and thus improving their power performance. However, it remains a grand challenge to achieve uniform precursors of LTO nanospheres and maintain their spherical structures after annealing. Herein, we develop a robust strategy for the synthesis of monodisperse LTO nanospheres with an average diameter of 120 nm via the use of titanium nitride (TiN) as a titanium source for lithium ion batteries (LIBs). The precursors composed of uniform TiO 2 /Li + nanospheres were formed in a stable alkaline environment during the course of heating of the solution of peroxo-titanium complex as a result of the dissolution of TiN, while TiO 2 /Li + microspheres were easily yielded with the decrease in pH value of the precursor solution. The OH − anion was found to effectively retard the hydrolysis of peroxo-titanium complex as well as the aggregation of TiO 2 /Li + nanoparticles. Intriguingly, a uniform polyvinyl pyrrolidone (PVP) layer formed in-situ on the surface of TiO 2 /Li + nanospheres rendered LTO to retain the monodisperse spherical morphology after annealing. Notably, the as-prepared monodisperse LTO nanospheres comprised of the interconnected LTO nanograins with an average size of ~15 nm uniformly coated by a carbon layer derived from the carbonization of PVP exhibited a high tap density (1.1 g cm −3 ) and an outstanding rate-cycling capability. The charge specific capacities at 1, 10, 50 and 80 C were 159.5, 151.1, 128.8 and 108.9 mAh g −1 , respectively. More importantly, the capacity retention after 500 cycles at 10 C was as high as 92.6%. This work opens up an avenue to craft the uniform precursors of LTO and thus monodisperse LTO nanospheres that possess superior rate performance with high volumetric energy densities and long-term cyclic stability.

High energy density LiNi0.8Co0.1Mn0.1O2 (NCM811)/Li metal batteries exhibit poor cycling due to the inferior structure stability of NCM811. Herein, a hierarchical cathode electrolyte interphase (CEI) with highly dense, resistive and protective properties is in-situ growth on NCM811 by decomposition reaction of lithium difluoro(oxalato)borate (LiDFOB). The hierarchical CEI presents special two-layered structure, where the inner layer is rich in LiF and outer layer mainly contains organic components such as LixBOyFz. The highly resistive inner layer can effectively prevent the NCM811 from further reacting with electrolyte and reduce the accumulation of organic products in outer layer during long cycling. Additionally, the LiDFOB can also induce the uniform deposition of Li ion, increase the Li plating/striping coulombic efficiency and inhibit the growth of Li dendrites. The NCM811/Li battery using LiDFOB presents a greatly improved rate and cycling performance. For instance, the NCM811/Li metal batteries using LiDFOB and LiPF6 based electrolyte delivers a specific capacity of 127.5 and 80.5 mAh g-1 at 10C, respectively and their capacity retentions are 69.8% and 17.1% after 400 cycles. The LiDFOB is a promising lithium salt for advanced high energy density NCM811/Li metal battery.

Exceptional capacities and excellent rate performance have been achieved by anodes made from electrospun carbon nanofibers (CNFs) that possess synergies of (i) functionalization with carbonyl and carboxyl groups, (ii) presence of nanopores and (iii) embedded graphene layers. The Fe precursor incorporated into the polyacrylonitrile melt functions as both catalyst for graphitization and sacrificial phases. CNFs are functionalized and nanopores surrounded by graphene layers are simultaneously created during the chemical etching of Fe3C particles from the CNFs. The pore size and volume could be tuned by controlling the Fe precursor content. Both the functional groups and nanopores are accessible to Li ions, and the satisfactory electrical conductivity arising from graphitization allows fast transfer of electrons. Remarkable capacities of 983 and 318 mAh g−1 are obtained when discharged at 100 and 3000 mA g−1, respectively, along with excellent capacity retention after 100 cycles.

This study is trying to demonstrate whether graphene is able to construct an effective conducting network for both electron and ion transports in cathode system of a high-power lithium ion battery (LIB), not based on a coin cell, but by employing a commercial soft-packaged 10 Ah battery pack as a model system. Compared with the cells using commercial conductive additive (7 wt% carbon black and 3 wt% conductive graphite), a 10 Ah cell using only 1 wt% graphene and 1 wt% carbon black shows lower internal resistance and higher energy density due to the excellent conductivity of graphene. However, owing to the fact that the planar structure of the graphene sheets blocks fast Li+ ion transport, the steric effect resulted heavy polarization occurs at a relatively high charge/discharge rate (>3 C). That is, although flexible and planar graphene helps construct an effective electron transfer network, it retards Li+ ion transport. Thus, for an energy-storing LIB with a low working charge/discharge rate, graphene additive shows apparent superiority over commercial ones even with much less addition fraction and may find its real commercial applications; while, for a high-power LIB which works at higher charge/discharge rate, fast ion transport path is required to be effectively constructed before a real application. Simulation results indicate that further work should be focused on the adjustment of electrode pore structure and modification of graphene steric structure accordingly to construct an unimpeded ion conducting network and provide high speed path for Li+ ion transport.