Advances in solid-state fiber batteries for wearable bioelectronics

Powering wearable bioelectronics with decent skin conformability and wearing comfort is highly desired. Fiber batteries could provide an attractive alternative to traditional rigid ones and present a compelling solution to this problem. In this review, we will discuss the various classes of fiber batteries, including lithium batteries, zinc batteries, and other types of fiber batteries. We will then report the latest research progress on each battery category through its working mechanism, materials usage, structure design, and wearable applications. Finally, we provide insights into current challenges and future applications of fiber batteries, aiming to promote the development of low-cost and high-performance fiber battery technologies for wearable bioelectronics.     

Inducing lattice defects in calcium ferrite anode materials for improved electrochemical performance in lithium-ion batteries

Enhancing the electrical conductivity of electrode materials via a cationic substitution strategy was recognized as an effective way of improving the electrochemical performance of Li-ion batteries. Thus, Li_xCa_1-xFe₂O₄ nanoparticles were synthesized via a facile inexpensive process at low temperature. XRD peaks refer to the formation of an orthorhombic structure with the Pnma space group. HR-TEM investigations reveal orthorhombic-like shape for pure CaFe₂O₄, nanoplatelet-like morphology for Li_0.05Ca_0.95Fe₂O₄ and irregular distorted crystals for Li_0.1Ca_0.9Fe₂O₄. Voids and pores in Li-doped CaFe₂O₄ were confirmed by FESEM and BET measurements. XPS spectra of O1s prove that Li-doped CaFe₂O₄ have higher conductivity due to the created lattice defects and oxygen species. Li-doped CaFe₂O₄ anodes exhibit great improvement in their initial discharge capacities ～1219 and 1606 mAhg^?1 upon substitution of Ca with 5% and 10% Li, respectively. Furthermore, 10% Li-doped CaFe₂O₄ anode displays the highest Li-ions diffusion coefficient and exchange current density due to the enhanced Li⁺ ions mobility. Moreover, the DC activation energies for the Li_xCa_1-xFe₂O₄ nanoparticles decreased with increasing Li content.     

MnS掺杂多孔碳复合材料的制备及电化学性能（两张发票1000+2500）

褐煤作为低级煤资源利用率不高，但褐煤中具有腐植酸成分，将褐煤中提取的腐植酸作为化肥原料，提取后剩余残渣作为碳源，与MnS纳米粒子制备了MnS@C复合材料。采用XRD、拉曼光谱、XPS、N2吸附-脱附、SEM和TEM对样品进行了表征。将该复合材料应用于锂离子电池负极材料，对其电化学性能进行了测试。结果表明，MnS@C复合材料的比表面积和孔容分别为117.19m2/g和0.044mL/g，该电极在0.1 A/g电流密度条件下循环200次后比容量高达830 mA‧h/g，且电极容量保持率为99%左右。在0.2、0.4、0.8、1.0、1.2和1.6 A/g电流密度下比容量分别为644、522、427、399、373和348mAh/g，展现出良好的倍率性能。MnS@C复合材料优异的电化学性能得益于碳基体的存在，不仅可以缓解MnS纳米粒子在嵌锂/脱锂过程中的体积膨胀，而且展示了锂离子电池高性能的巨大潜力，为褐煤的高值化利用作出巨大贡献。     

Centrifugally spun carbon fibers prepared from aqueous poly(vinylpyrrolidone) solutions as binder-free anodes in lithium-ion batteries

Aqueous solutions of poly(vinylpyrrolidone) (PVP) of various concentrations (20, 25, and 28 wt%) were successfully spun into fibers by centrifugal spinning. The pristine PVP fibers were annealed and carbonized to produce flexible carbon fibers for use as binder-free anodes in lithium-ion batteries. These flexible carbon fibers were prepared by developing a novel three-step heat treatment to reduce the residual stresses in the pristine PVP precursor fibers, and to prevent fiber degradation during carbonization. The thermogravimetric analysis data showed that the annealed fibers yielded a residual mass percentage of 36.0% while the pristine PVP fibers suffered a higher mass loss and only retained 26.5% of original mass above 450 °C (under nitrogen). The electrochemical performance of the carbon-fiber anodes was evaluated by conducting galvanostatic charge/discharge, rate performance, and cycle voltammetry experiments. The 20, 25, and 28 wt% derived binder-free anodes delivered specific charge capacities of 205, 189, and 275 mAh g⁻¹, respectively, after the first cycle at a current density of 100 mA g⁻¹. The results obtained in this work indicate that a feasible pathway towards a large-scale production of carbon-fiber anodes from a 100% aqueous solution can be achieved via centrifugal spinning and subsequent heat treatment.     

Hollow multi-nanochannel carbon nanofiber/MoS2 nanoflower composites as binder-free lithium-ion battery anodes with high capacity and ultralong-cycle life at large current density

The electrode materials with high pseudocapacitance can enhance the rate capability and cycling stabil-ity of lithium-ion storage devices.Herein,we fabricated MoS2 nanoflowers with ultra-large interlayer spacing on N-doped hollow multi-nanochannel carbon nanofibers(F2-MoS2/NHMCFs)as freestanding binder-free anodes for lithium-ion batteries(LIBs).The ultra-large interlayer spacing(0.78～1.11 nm)of MoS2 nanoflowers can not only reduce the internal resistance,but also increase accessible active sur-face area,which ensures the fast Li+intercalation and deintercalation.The NHMCFs with hollow and multi-nanochannel structure can accommodate the large internal strain and volume change during lithi-ation/delithiation process,it is beneficial to improving the cycling stability of LIBs.Benefiting from the above combined structure merits,the F2-MoS2/NHMCFs electrodes deliver a high rate capability 832 mA h g-1 at 10 A g-1 and ultralong cycling stability with 99.29 and 91.60％capacity retention at 10 A g-1 after 1000 and 2000 cycles,respectively.It is one of the largest capacities and best cycling stability at 10 A g-1 ever reported to date,indicating the freestanding F2-MoS2/NHMCFs electrodes have potential applications in high power density LIBs.     

Toward High-Performance Dihydrophenazine-Based Conjugated Microporous Polymer Cathodes for Dual-Ion Batteries through Donor–Acceptor Structural Design

Recent studies have demonstrated that dihydrophenazine (Pz) with high redox-reversibility and high theoretical capacity is an attractive building block to construct p-type polymer cathodes for dual-ion batteries. However, most reported Pz-based polymer cathodes to date still suffer from low redox activity, slow kinetics, and short cycling life. Herein, a donor–acceptor (D–A) Pz-based conjugated microporous polymer (TzPz) cathode is constructed by integrating the electron-donating Pz unit and the electron-withdrawing 2,4,6-triphenyl-1,3,5-triazine (Tz) unit into a polymer chain. The D–A type structure enhances the polymer conjugation degree and decreases the band gap of TzPz, facilitating electron transportation along the polymer skeletons. Therefore the TzPz cathode for dual-ion battery shows a high reversible capacity of 192 mAh g⁻¹ at 0.2 A g⁻¹ with excellent rate performance (108 mAh g⁻¹ at 30 A g⁻¹), which is much higher than that of its counterpart polymer BzPz produced from 1,3,5-triphenylbenzene (Bz) and Pz (148 and 44 mAh g⁻¹ at 0.2 and 10 A g⁻¹, respectively). More importantly, the TzPz cathode also shows a long and stable cyclability of more than 10 000 cycles. These results demonstrate that the D–A structural design is an efficient strategy for developing high-performance polymer cathodes for dual-ion batteries.     

Lithiophilic MXene-Guided Lithium Metal Nucleation and Growth Behavior

The positive effects of a lithiophilic substrate on the electrochemical performance of lithium metal anodes are confirmed in several reports, while the understanding of lithiophilic substrate-guided lithium metal nucleation and growth behavior is still insufficient. In this study, the effect of a lithiophilic surface on lithium metal nucleation and growth behaviors is investigated using a large-area Ti₃C₂T_x MXene substrate with a large number of oxygen and fluorine dual heteroatoms. The use of the MXene substrate results in a high lithium-ion concentration as well as the formation of uniform solid–electrolyte-interface (SEI) layers on the lithiophilic surface. The solid–solid interface (MXene-SEI layer) significantly affects the surface tension of the deposited lithium metal nuclei as well as the nucleation overpotential, resulting in the formation of uniformly dispersed lithium nanoparticles ( ≈ 10–20 nm in diameter) over the entire MXene surface. The primary lithium nanoparticles preferentially coalesce and agglomerate into larger secondary particles while retaining their primary particle shapes. Subsequently, they form close-packed structures, resulting in a dense metal layer composed of particle-by-particle microstructures. This distinctive lithium metal deposition behavior leads to highly reversible cycling performance with high Columbic efficiencies >  99.0% and long cycle lives of over 1000 cycles.     

Direct View on the Origin of High Li+ Transfer Impedance in All-Solid-State Battery

Large interfacial resistance plays a dominant role in the performance of all-solid-state lithium-ion batteries. However, the mechanism of interfacial resistance has been under debate. Here, the Li⁺ transport at the interfacial region is investigated to reveal the origin of the high Li⁺ transfer impedance in a LiCoO₂(LCO)/LiPON/Pt all-solid-state battery. Both an unexpected nanocrystalline layer and a structurally disordered transition layer are discovered to be inherent to the LCO/LiPON interface. Under electrochemical conditions, the nanocrystalline layer with insufficient electrochemical stability leads to the introduction of voids during electrochemical cycles, which is the origin of the high Li⁺ transfer impedance at solid electrolyte-electrode interfaces. In addition, at relatively low temperatures, the oxygen vacancies migration in the transition layer results in the formation of Co₃O₄ nanocrystalline layer with nanovoids, which contributes to the high Li⁺ transfer impedance. This work sheds light on the mechanism for the high interfacial resistance and promotes overcoming the interfacial issues in all-solid-state batteries.     

Nido-Hydroborate-Based Electrolytes for All-Solid-State Lithium Batteries

Hydroborate-based solid electrolytes have recently been successfully employed in high voltage, room temperature all-solid-state sodium batteries. The transfer to analogous lithium systems has failed up to now due to the lower conductivity of the corresponding lithium compounds and their high cost. Here LiB₁₁H₁₄ nido-hydroborate as a cost-effective building block and its high-purity synthesis is introduced. The crystal structures of anhydrous LiB₁₁H₁₄ as well as of LiB₁₁H₁₄-based mixed-anion solid electrolytes are solved and high ionic conductivities of 1.1 × 10⁻⁴ S cm⁻¹ for Li₂(B₁₁H₁₄)(CB₁₁H₁₂) and 1.1 × 10⁻³ S cm⁻¹ for Li₃(B₁₁H₁₄)(CB₉H₁₀)₂ are obtained, respectively. LiB₁₁H₁₄ exhibits an oxidative stability limit of 2.6 V versus Li⁺/Li and the proposed decomposition products are discussed based on density functional theory calculations. Strategies are discussed to improve the stability of these compounds by modifying the chemical structure of the nido-hydroborate cage. Galvanostatic cycling in symmetric cells with two lithium metal electrodes shows a small overpotential increase from 22.5 to 30 mV after 620 h (up to 0.5 mAh cm⁻²), demonstrating that the electrolyte is compatible with metallic anodes. Finally, the Li₂(B₁₁H₁₄)(CB₁₁H₁₂)  electrolyte is employed in a proof-of-concept half cell with a TiS₂ cathode with a capacity retention of 82% after 150 cycles at C/5.     

Studies on spinel cobaltites,MCo2O4 (M = Mn,Zn, Fe,Ni and Co) and their functional properties

Optimization of electrodes for charge storage with appropriate processing conditions places significant challenges in the developments for high performance charge storage devices. In this article, metal cobaltite spinels of formula MCo₂O₄ (where M = Mn, Zn, Fe, Ni and Co) are synthesized by oxalate decomposition method followed by calcination at three typical temperatures, viz. 350, 550, and 750 °C and examined their performance variation when used as anodes in lithium ion batteries. Phase and structure of the materials are studied by powder x-ray diffraction (XRD) technique. Single phase MnCo2O4,ZnCo2O4 and Co3O4 are obtained for all different temperatures 350 °C, 550 °C and 750 °C; whereas FeCo₂O₄ and NiCo₂O₄ contained their constituent binary phases even after repeated calcination. Morphologies of the materials are studied via scanning electron microscopy (SEM): needle-shaped particles of MnCo₂O₄ and ZnCo₂O₄, submicron sized particles of FeCo₂O₄ and agglomerated submicron particle of NiCo₂O₄ are observed. Galvanostatic cycling has been conducted in the voltage range 0.005–3.0 V vs. Li at a current density of 60 mA g^?1 up to 50 cycles to study their Li storage capabilities. Highest observed charge capacities are: MnCo₂O₄ – 365 mA h g^?1 (750 °C); ZnCo₂O₄ – 516 mA h g^?1 (550 °C); FeCo₂O₄ – 480 mA h g^?1 (550 °C); NiCo₂O₄ – 384 mA h g^?1 (750 °C); and Co₃O₄ – 675 mA h g^?1 (350 °C). The Co₃O₄ showed the highest reversible capacity of 675 mA h g^?1; the NiO present in NiCo₂O₄ acts as a buffer layer that results in improved cycling stability; the ZnCo₂O₄ with long needle-like shows good cycling stability.