Realizing the Embedded Growth of Large Li₂O₂ Aggregations by Matching Different Metal Oxides for High‐Capacity and High‐Rate Lithium Oxygen Batteries

Abstract

Large Li2O2 aggregations can produce high‐capacity of lithium oxygen (Li‐O2) batteries, but the larger ones usually lead to less‐efficient contact between Li2O2 and electrode materials. Herein, a hierarchical cathode architecture based on different discharge characteristics of α‐MnO2 and Co3O4 is constructed, which can enable the embedded growth of large Li2O2 aggregations to solve this problem. Through experimental observations and first‐principle calculations, it is found that α‐MnO2 nanorod tends to form uniform Li2O2 particles due to its preferential Li+ adsorption and similar LiO2 adsorption energies of different crystal faces, whereas Co3O4 nanosheet tends to simultaneously generate Li2O2 film and Li2O2 nanosheets due to its preferential O2 adsorption and different LiO2 adsorption energies of varied crystal faces. Thus, the composite cathode architecture in which Co3O4 nanosheets are grown on α‐MnO2 nanorods can exhibit extraordinary synergetic effects, i.e., α‐MnO2 nanorods provide the initial nucleation sites for Li2O2 deposition while Co3O4 nanosheets provide dissolved LiO2 to promote the subsequent growth of Li2O2. Consequently, the composite cathode achieves the embedded growth of large Li2O2 aggregations and thus exhibits significantly improved specific capacity, rate capability, and cyclic stability compared with the single metal oxide electrode.

Hierarchical NiCo2S4@NiO Core–Shell Heterostructures as Catalytic Cathode for Long‐Life Li‐O2 Batteries

“…The detailed FTIR spectra of the discharged and charged NiCo 2 S 4 @NiO, NiCo 2 S 4 , and NiO electrodes at the 40th cycle are demonstrated in Figure S14 (Supporting Information). [12,26] In addition, the peaks at 1195 and 1403 cm −1 associated with CH 3 COOLi and 1353, 1619, and 1639 cm −1 indexed to HCOOLi are detected. [26,51] However, the characteristic absorption peaks of side reaction products (Li 2 CO 3 , HCOOLi, CH 3 COOLi) can be distinctly observed in both the discharged/ charged NiCo 2 S 4 and NiO electrodes, meaning much inferior rechargeability.…”

“…The large size of peasecod-like Li 2 O 2 accommodations endows higher discharge capacity for the NiCo 2 S 4 @ NiO electrode. [13,26] As shown in Figure S10f www.advenergymat.de www.advancedsciencenews.com peasecod-like Li 2 O 2 agglomerations intimately and homogeneously wrapping around the CP backbones after discharge, the NiCo 2 S 4 /NiO composite electrode can achieve striking ameliorations in specific capacity and discharge/charge overpotential at the same time. As a consequence, through the connected diffusion channels and large interfaces between NiCo 2 S 4 /NiO composite catalyst and Li 2 O 2 , the fast transport of Li + and electron could be efficiently promoted during the following charge process, resulting in high reversibility, outstanding catalytic efficiency, and small OER overpotential, which is critical for practical energy storage technology in Li-O 2 battery system.…”

“…2019, 9,1900788 The peasecod-like Li 2 O 2 displays a length of 3-5 µm and a diameter of 200 nm. [11,12,26] As for the discharged NiO electrode in Figure 6e,f and Figure S10e (Supporting Information), Li 2 O 2 nanosheets are formed on the NiO matrices surface with an irregularly embedded state. It is worth noting that the breathable open structure is robust even at the full-discharged state, and still provides diffusion channels without thoroughly passivating by discharge products.…”

“…The galvanostatic discharge/charge patterns of NiCo 2 S 4 @NiO, NiCo 2 S 4 , and NiO electrodes at different current densities (200, 400, and 1000 mA g −1 ) in the voltage window of 2.0-4.5 V versus Li/Li + are recorded in Figure 4e and Figure S7a,b (Supporting Information). [18,26] For instance, with the current density increasing, NiCo 2 S 4 @NiO electrode delivers discharge capacities of 8675 mAh g −1 at 400 mA g −1 and 6120 mAh g −1 at 1.0 A g −1 . With an increase of the current density, both of the obtained capacity and polarization are deteriorated especially for the charge overpotential for all the electrodes, which can be assigned to the internal charge transfer impedance of the batteries.…”

“…[26] Dong's group constructed an open-structured Co 9 S 8 matrix realizing large hydrangea-like Li 2 O 2 aggregations that could yield huge discharge capacity and exhibit lower charge overpotential simultaneously. For example, Yan's group reported the embedded growth of large Li 2 O 2 aggregates on cathode surface with preferable OER polarization by virtue of different catalytic properties of α-MnO 2 and Co 3 O 4 .…”