Metal-bio-oxygen batteries establish a paradigm-shifting energy architecture for biomedical implants, endowing these devices with extended service life in continuous physiological surveillance and precision theranostic operations. However, the conventional electrolytes in these semi-opened batteries fail to meet the requirements in bio-compatibility and bio-safety for in vivo applications. Herein, we report a bio-compatible composite gel electrolyte for implanted Zn-O₂ battery (ZOB), while also sustainably powering a mechanical sensor in vivo. This electrolyte composes a poly(L-lactide-co-epsilon-caprolactone) (PLCL) framework with a gelatin methacryloyl (GelMA) modification layer, and the salt in body fluid serves as ion transport carriers in the electrolyte. It displays an O₂ impermeable property and lower polarization potentials as electrolyte in Zn||Zn symmetric cell. In vitro assay results demonstrate that the battery components illustrate excellent biocompatibility with negligible cytotoxicity. In vivo histopathological and hematological analyses further verified the biosafety of ZOB during operation, while capillary regeneration around the cathode ensured adequate oxygen supply for sustained performance. The assembled ZOB delivers a power density of 1.96 μW/cm² at 0.98 V in vivo, which also successfully powers an integrated hydrogel mechanical sensor and monitors cardiac signals in rats. The unique two-electron transfer pathway of oxygen reduction in blood has also been elucidated. This work offers a new insight into bio-compatible electrolyte design for next-generation implantable power sources, enabling robust implantable devices for healthcare technologies.

Thick electrode, with its feasibility and cost-effectiveness in lithium-ion batteries (LIBs), has attracted significant attention as a promising approach maximizing the energy density of battery. Through raising the mass loading of active materials without altering the fundamental chemical attributes, thick electrodes can boost the energy density of the batteries effectively. Nevertheless, as the thickness of the electrode increases, the ionic conductivity of the electrode decreases, leading to abominable polarization in the thickness direction, which severely hampers the practical application of a thick electrode. This work proposes a novel porous gradient design of high-performance thick electrodes for LIBs. By constructing a porous structure that serves as a fast transport pathway for lithium (Li) ions, the ion transport kinetics within thick electrodes are significantly enhanced. Meanwhile, a particle size gradient design is incorporated to further mitigate polarization effects within the electrode, leading to substantial improvements in reaction homogeneity and material utilization. Employing this strategy, we have fabricated a porous gradient nanocellulose-carbon-nanotube based thick electrode, which exhibits an impressive capacity retention of 86.7% at a high mass loading of LiCoO₂ (LCO) active material (20 mg cm⁻²) and a high current density of 5 mA cm⁻².

Li₂C₂O₄, with a high theoretical capacity of 525 mAh·g⁻¹ and good air stability, is regarded as a more attractive cathode pre-lithiation additive in contrast to the reported typical inorganic pre-lithiation compounds which are quite air sensitive. However, its obtained capacity is much lower than the theoretical value and its delithiation potential (> 4.7 V) is too high to match with the most commercial cathode materials, which greatly impedes its practical application. Herein, we greatly improve the pre-lithiation performance of Li₂C₂O₄ as cathode additive with fulfilled capacity at a much-reduced delithiation voltage, enabling its wide applicability for typical commercial cathodes. We increase the capacity of Li₂C₂O₄ from 436 to 525 mAh·g⁻¹ by reducing its particle size. Through optimizing the types of conductive additives, introducing nano-morphological NiO, MnO₂, etc. as catalysts, and innovatively designing a bilayer electrode, the delithiation potential of Li₂C₂O₄ is successfully reduced from 4.778 to 4.288 V. We systematically study different particle size, conductive additives, and catalysts on the delithiation behavior of Li₂C₂O₄. Finally, it is applied to pre-lithiate the hard carbon anode, and it is found that Li₂C₂O₄ could effectively increase the capacity of the full cell from 79.0 to 140.0 mAh·g⁻¹ in the first cycle. In conclusion, our study proves that improving the reactivity is an effective strategy to boost the pre-lithiation of Li₂C₂O₄.

Among the alloying-type anodes, elemental Sb possesses the suitable yet safe plateau, simple lithiation pathway, small voltage polarization, high conductivity, and superior cycle stability. However, challenge is that its intrinsic capacity is rather low (660 mAh g⁻¹), <1/6 of silicon. Herein, we propose a seamless integration strategy by merging the voltage and capacity of phosphorus and antimony into a solid solution alloy. Interestingly, the enlistment of P is found greatly enlarge the capacity from 660 to 993 mAh g⁻¹ for such Sb₃₀P₃₀ solid solution, while maintaining a single and stable discharge plateau (~0.79 V) similar to elemental Sb. Various experimental characterizations including XPS, PDF, Raman, and EDS mapping reveal that in such a material the P and Sb atoms have interacted with each other to form a homogenous solid solution alloy, rather than a simple mixing of the two substances. Thus, the Sb₃₀P₃₀ exhibits superior rate performances (807 mAh g⁻¹ at 5000 mA g⁻¹) and cyclability (821 mAh g⁻¹ remained after 300 cycles). Furthermore, such Sb_60-xP_x alloys can even deliver 621 mAh g⁻¹ at −30℃, which can be served as the alternative anode materials for high-energy and low-temperature batteries. This unique seamless integration strategy based on solid solution chemistry can be easily leveraged to manipulate the capacity of other electrode materials at similar voltage.