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The desperate pursuit of high gravimetric specific energy leads to the ignorance of volumetric energy density that is one of the basic requirements for batteries. Due to the high volumetric capacity, less‐prone formation of dendrite, and low reduction potential of Mg metal, rechargeable Mg batteries are considered with innately high volumetric energy density. Nevertheless, the substantial elevation in energy density is compromised by extremely excessive Mg metal anode. Herein, the proof‐of‐concept of anode‐free Mg2Mo6S8‐MgS/Cu batteries is proposed, in which MgS as the premagnesiation additive constantly decomposes to replenish Mg loss by electrolyte corrosion over cycling, while both Mg2Mo6S8 and MgS acts as the active material to reversibly provide high capacities. Besides, Mg2Mo6S8 shows superior catalytic activity on the decomposition of MgS and provides the strong affinity to polysulfides to restrain their dissolution. Consequently, the anode‐free Mg2Mo6S8‐MgS/Cu batteries deliver a high reversible capacity of 190 mAh g−1 with the capacity retention of 92% after 100 cycles, corresponding to the highly competitive energy density of 420 Wh L−1. The proposed anode‐free Mg battery here spotlights the great promise of Mg batteries in achieving high volumetric energy densities, which will significantly expedite the advances of Mg batteries in practice. [ABSTRACT FROM AUTHOR]

Anode‐free lithium metal batteries can maximize the energy density at the cell level. However, without the Li compensation from the anode side, it faces much more challenging to achieve a long cycling life with a competitive energy density than Li metal‐based batteries. Here, we prolong the lifespan of an anode‐free Li metal battery by introducing Li‐rich Li2[Ni0.8Co0.1Mn0.1]O2 into the cathode as a Li‐ions extender. The Li2[Ni0.8Co0.1Mn0.1]O2 can release a large amount of Li‐ions during the first charging process to supplement the Li loss in the anode, then convert into NCM811, thus extending the lifespan of the battery without the introduction of inactive elements. By the benefit of Li‐rich cathode and high reversibility of Li metal on Cu foil, the anode‐free pouch cells enable to achieve 447 Wh kg−1 energy density and 84 % capacity retention after 100 cycles in the condition of limited electrolyte addition (E/C ratio of 2 g Ah−1). [ABSTRACT FROM AUTHOR]

Anode‐free designs can obtain the ultimate energy density of lithium metal batteries. However, without a continuous Li supply from the anode side, it is much more challenging to achieve high capacity retention with a competitive energy density. Here, the lifespan of an anode‐free Li metal battery is prolonged by applying an epitaxial induced plating current‐collector (E‐Cu). The functional layer on E‐Cu initiates Li storage by an alloying approach, forming an epitaxial induce layer, which exhibits speedy surface diffusion for of Li‐ions, resulting in the block like epitaxial growth of Li. Moreover, this alloying process also promotes the formation of a LiF‐rich solid electrolyte interphase (SEI), which is very useful for uniform Li plating. Due to the benefits of epitaxial Li plating and LiF‐rich SEI, the initial coulombic efficiency of the E‐Cu/Li asymmetric cell increases from 93.24 to 98.24%, and the capacity retention of anode‐free NCM811/E‐Cu pouch cell increases from 66 to 84% with a remarkable energy density of 420 Wh kg−1 in the condition of limited electrolyte addition (E/C ratio of 2 g Ah−1). This strategy is promising in the development of high energy batteries in extending their lifespans. [ABSTRACT FROM AUTHOR]