The operation of deep-sea underwater vehicles relies entirely on onboard batteries. However, the extreme deep-sea conditions, characterized by ultrahigh hydraulic pressure, low temperature, and seawater conductivity, pose significant challenges for battery development. These conditions drive the need for specialized designs in deep-sea batteries, incorporating critical aspects of power generation, protection, distribution, and management. Over time, deep-sea battery technology has evolved through multiple generations, with lithium (Li) batteries emerging in recent decades as the preferred power source due to their high energy and reduced operational risks. Although the rapid progress of Li batteries has notably advanced the capabilities of underwater vehicles, critical technical issues remain unresolved. This review first systematically presents the whole picture of deep-sea battery manufacturing, focusing on Li batteries as the current mainstream solution for underwater power. It examines the key aspects of deep-sea Li battery development, including materials selection informed by electro-chemo-mechanics models, component modification and testing, and battery management systems specialized in software and hardware. Finally, it discusses the main challenges limiting the utilization of deep-sea batteries and outlines promising directions for future development. Based on the systematic reflection on deep-sea batteries and discussion on deep-sea Li batteries, this review aims to provide a research foundation for developing underwater power tailored for extreme environmental exploration.

Benefiting from the distinctive ordering degree and local microstructure characteristics, hard carbon (HC) is considered as the most promising anode for sodium-ion batteries (SIBs). Unfortunately, the low initial Coulombic efficiency (ICE) and limited reversible capacity severely impede its extensive application. Here, a homogeneous curly graphene (CG) layer with a micropore structure on HC is designed and executed by a simple chemical vapor deposition method (without catalysts). CG not only improves the electronic/ionic conductivity of the hard carbon but also effectively shields its surface defects, enhancing its ICE. In particular, due to the spontaneous curling structural characteristics of CG sheets (CGs), the micropores (≤ 2 nm) formed provide additional active sites, increasing its capacity. When used as a sodium-ion battery anode, the HC-CG composite anode displayed an outstanding reversible capacity of 358 mAh·g⁻¹, superior ICE of 88.6%, remarkable rate performance of 145.8 mAh·g⁻¹ at 5 A·g⁻¹, and long cycling life after 1000 cycles with 88.6% at 1 A·g⁻¹. This work provides a simple defect/microstructure turning strategy for hard carbon anodes and deepens the understanding of Na⁺ storage behavior in the plateau region, especially on the pore-filling mechanism by forming quasi-metallic clusters.

Rechargeable Mg-ion batteries (MIBs) have attracted much more attentions by virtue of the high capacity from the two electrons chemistry. However, the reversible Mg²⁺ diffusion in cathode materials is restricted by the strong interactions between the high-polarized bivalent Mg²⁺ ions and anionic lattice. Herein, we design and propose a hetero-structural VO₂(R)-VS₄ cathode, in which the re-delocalized d-electrons can effectively shield the polarity of Mg²⁺ ions. Theoretically, the electrons should spontaneously transfer from VS₄ to VO₂(R) through the interfaces of hetero-structure due to the lower work function value of VS₄. Furthermore, the internal electrons transfer lead to the electronic injection into VO₂(R) from VS₄ and the partially broken V-V dimers, indicating the presence of lone pair electrons and charge re-delocalization. Benefiting from the shield effect of re-delocalized electrons, and the weakened attraction between cations and O/S anions enables more S²⁻-S₂²⁻ redox groups to participate the electrochemical reactions and compensate the double charge of Mg²⁺ ions. Accordingly, VO₂(R)-VS₄ hetero-structure exhibits a high specific capacity of 554 mA h g⁻¹ at 50 mA g⁻¹. It is believed that the charge re-delocalization of cathode extremely boost the Mg²⁺ ions migration for the high-capacity of MIBs.

Printed micro-supercapacitor exhibits its flexibility in geometry design and integration, showing unprecedented potential in powering the internet of things and portable devices. However, the printing process brings undesired processing defects (e.g., coffee ring effect), resulting in severe self-discharge of the printed micro-supercapacitors. The impact of such problems on device performance is poorly understood, limiting further development of micro-supercapacitors. Herein, by analyzing the self-discharge behavior of fully printed micro-supercapacitors, the severe self-discharge problem is accelerated by the ohmic leakage caused by the coffee ring effect on an ultrathin polymer electrolyte. Based on this understanding, the coffee ring effect was successfully eradicated by introducing graphene oxide in the polymer electrolyte, achieving a decline of 99% in the self-discharge rate. Moreover, the micro-supercapacitors with uniformly printed polymer electrolyte present 7.64 F cm^-3 volumetric capacitance (14.37 mF cm^-2 areal capacitance), exhibiting about 50% increase compared to the one without graphene oxide addition. This work provides a new insight to understand the relationship between processing defects and device performance, which will help improve the performance and promote the application of printed micro-supercapacitors.