Surface Modification of Li‐Rich Mn‐Based Layered Oxide Cathodes: Challenges, Materials, Methods, and Characterization

Abstract

high energy and power density, long cycle life, low cost, and environmental benignity. [3] Due to the high capacity of the currently used graphite anode −372 mAh g-1 , [1b,4] commercial cathodes have become the bottleneck for improving the energy density. [5] In addition, cathode materials take up about 40% of the total material cost of typical LIB cells. It is therefore crucial to develop cathode materials with high energy density and low cost, while maintaining superior safety features. [6] Driven by the wide deployment of electric vehicles in recent years, the demand for safer cathode materials with higher capacity and lower cost has become imperative. [2b] The specific capacity depends on the inherent physical properties of the cathode materials. Commercial materials such as LiCoO 2 , Li(Ni x Mn y Co z)O 2 , Li(Ni x Co y Al z)O 2 , LiMn 2 O 4 and LiFePO 4 all possess discharge capacities below 200 mAh g-1. [7] Ni-rich NCM, NCA, and Li-rich oxides are all prospective cathodes for high-energy LIBs as they can exhibit high specific discharge capacities above 200 mAh g-1. [6c] As compared with Ni-rich NCM and NCA, Li-rich Mn-based layered oxide (LMLO) cathode materials are cheaper and have higher specific capacity. They can deliver an initial specific discharge capacity that approaches 300 mAh g-1 , nearly doubling the capacity of commercially used cathodes and close to the limit for lithiated transition metal oxides. [8] Figure 1 lists the main development milestones of LMLO. In 1997 a novel material, LiCoO 2-Li 2 MnO 3 , was found by Numata et al., [9] a discovery that initiated intensive work on high energy density cathode materials. This group studied these materials intensively and demonstrated their cycling stability in the range of 3.0-4.3 V versus Li. [10] In 1999, Kalyani et al. reported that Li 2 MnO 3 can undergo electrochemical activation at potentials >4.5 V versus Li. [11] Dahn et al. described the charge compensation mechanism of LMLO, [12] and these cathodes were shown to provide high capacity at high operational voltage (>4.5 V). [13] In 2004, Thackeray et al. explored xLi 2 M′O 3-(1-x)LiMn 0.5 Ni 0.5 O 2 cathode materials with M′ = Zn, Ti, or Mn, concluding that Li 2 M′O 3 and LiMn 0.5 Ni 0.5 O 2 in these composite materials were integrated by short-range interactions. [14] The following Rechargeable lithium-ion batteries have become the dominant power sources for portable electronic devices, and are regarded as the battery technology of choice for electric vehicles and as potential candidates for grid-scale storage. Commercial lithium-ion batteries, after three decades of cell engineering, are approaching their energy density limits. Toward continually improving the energy density and reducing cost, Li-rich Mn-based layered oxide (LMLO) cathodes are receiving more and more attention due to their high discharge capacity and low cost. However, commercialization has been hampered by severe capacity and voltage decay, sluggish rate capability, and poor safety performance during charge/discharge cyc...

Boron-doped sodium layered oxide for reversible oxygen redox reaction in Na-ion battery cathodes

“…Inert surface coating of metal oxide (Al 2 O 3 , MgO) 20 , 21 or metal phosphate (NaPO 3 , β-NaCaPO 4 ) 17 , 22 were utilized to stabilize the crystal structure through suppressing surface irreversible phase transformation from irreversible oxygen redox reaction. Alternatively, the doping of inactive cations (Ti 4+ , Se 6+ , Nb 5+ ) 23 – 25 is used to increase the oxygen binding energy effectively 26 , alleviating the irreversible oxygen redox reaction and promoting the stability of crystal structure 27 – 29 . However, it is still challenging to achieve a highly homogenous coating layer on the surface of cathode particles.…”

Future Material Developments for Electric Vehicle Battery Cells Answering Growing Demands from an End-User Perspective

“…The higher electronegativity of Sn 4+ with respect to Mn 4+ leads to stronger structural bonds which improve cycling performance of the material with respect to parent LNMO [129] (Figure 2). Other interesting approaches are particle encapsulation using a conductive layer [130] or surface modification [131,132]. Both approaches have shown improved kinetics and cycling performances with respect to bare materials.…”

Intelligent phase-transition MnO2 single-crystal shell enabling a high-capacity Li-rich layered cathode in Li-ion batteries

“…12 Extensive efforts have been made to inhibit cation/anion loss. Surface modication, [13][14][15][16] body phase doping, [17][18][19][20] and gradient treatment 21,22 have been successfully used for this purpose because the irreversible loss of oxygen mainly occurs on the material surface. 23,24 Surface modication can greatly improve the stability and dynamic performance of surface oxygen 25 which enhances the specic capacity and regulates the cycling stability of materials.…”