Unveiling Conversion Reaction on Intercalation‐Based Transition Metal Oxides for High Power, High Energy Aqueous Lithium Battery

Abstract

required for the operation of dangerous flammable electrolytes inevitably incur substantial cost, which introduces more difficulties in fabrication of large scale energy storage systems. [5] To tackle these safety and sustainability concerns at their roots, aqueous lithium-ion batteries (ALiBs) were first proposed in 1994, and has since drawn significant attention. [6][7][8] However, due to limited practical capacity of cathode materials based on Li + intercalation mechanism (between 110 and 140 mAh g −1 ) [9,10] and the narrow electrochemical stability window (avoiding hydrogen and oxygen evolution, generally not exceeding 1.2 V), [11,12] the package-level energy density, even in its ceiling value is normally less than 50 Wh kg −1 , which cannot meet the requirements of commercial electrical vehicles, such as Nissan Leaf and Tesla Model S. [13,14] It has been also reported that based on Li + adsorption mechanism on both sides of MnO 2 monolayer, a high theoretical capacity up to 616 mAh g −1 can be obtained. [15] However, this value is only on the basis of first-principles calculations, and more experimental evidence is needed. As a result, breakthroughs in performance of ALiBs are required, which may only come from the development of novel concepts in energy storage mechanism, probably different from intercalation chemistry.Recently, conversion reactions in transition metal oxide structures (e.g., MnO x , CoO x , and CuO x ) with Li + have been reported to show a large, rechargeable capacity in lithium-ion cells of organic electrolytes. [16][17][18] The specific capacity of these materials can be as high as 1000 mAh g −1 (about seven times that of common Li + intercalation materials), [19] which can potentially boost the energy density of lithium-ion batteries. However, in contrast to that of organic electrolyte systems where cathode and anode materials often operate under high conversion potentials, [20] the operating potential window in aqueous electrolyte batteries is far below the thermodynamic voltage limit of cathode and anode materials. [19] Therefore, a conversion reaction between transition metal oxides and alkaline metals (or ions) in ALiBs has been believed impossible. [21,22] In this study, against the conventional belief, we report that a reversible conversion reaction can happen between Li + and semicrystalline MnO 2 (scMO) prepared from a conventional Aqueous lithium batteries are reaching their energy and power limits partly due to limited capacity from intercalation chemistry. Alternatively, conversion reactions bring added capacity that can significantly increase the capacity ceiling of the cell. However, such reactions can only be realized in organic electrolytes, and similar redox chemistry in aqueous lithium batteries is not reported yet. In this work, it is discovered that a large work function difference (up to 1.78 eV) between crystalline LiMn 2 O 4 (cLMO) and semicrystalline MnO 2 (scMO) makes energy bands of MnO 2 bend downward toward their interface, resulting in the accumulation of f...

Understanding the active formation of a cathode–electrolyte interphase (CEI) layer with energy level band bending for lithium-ion batteries

“…The results of the Mn oxidation states corroborate previous studies. 38,39 After the electrochemical cycles, the signal of Mn 2p became weaker, suggesting the dissolution of Mn in the electrolyte. One pair of spin–orbit doublet Ni (2p 3/2 ) and Ni (2p 1/2 ) peaks were observed at 854.9 eV and 872.7 eV, respectively, followed by shake-up peaks at 860.7 eV and 879.2 eV at the reference state as can be seen in Fig.…”

Vertically Aligned and Ordered Arrays of 2D MCo2S4@Metal with Ultrafast Ion/Electron Transport for Thickness-Independent Pseudocapacitive Energy Storage

“…The multiple plateaus in the charge–discharge process (Figure e) indicate multistep reactions because of the coexistence of Ni 2+ /Ni 3+ and Co 2+ /Co 3+ ions. The plateau in the discharge process is caused by the ion deintercalation . The duration of the plateau is positively correlated with the mass loading of electrode material ( t R ≤ 5 h).…”

“…The plateau in the discharge process is caused by the ion deintercalation. 51 The duration of the plateau is positively correlated with the mass loading of electrode material (t R ≤ 5 h). For the HS-5, the plateau exhibits a long period at 0.1 V due to high mass loading.…”

A Comprehensive Understanding of Interlayer Engineering in Layered Manganese and Vanadium Cathodes for Aqueous Zn‐Ion Batteries

“…Compared with the popular intercalation chemistry, a chemistry conversion reaction in a battery would tend to achieve higher capacity owing to the direct charge transfer in the reactions that possess a superior theoretic capacity [61] . Thus, introducing a reasonable conversion reaction is a promising and effective solution to build high‐performance AZIBs.…”