Systematic Study of Different Anion Doping on the Electrochemical Performance of Cobalt-Free Lithium–Manganese-Rich Layered Cathode

Abstract

Regardless of the appealingly high energy density (1000 Wh kg–1) of the lithium–manganese-rich layered oxide cathode (LMR-NMO), this material still suffers from rapid capacity and voltage decay after continuous cycling. LMR-NMO involves the redox reaction of both transition metals and oxygen to gain additional capacity in comparison with a conventional NMC cathode. Due to the use of a high voltage range (beyond 4.4 V), the oxygen release from the structure initiates and in turn generates intergranular cracks and spinel formation, consequently, into rock-salt structure. Here, LMR-NMO with different doping ranges (1–5 mol %) of F, S, and Cl are being examined to summarize the benefits and drawbacks of each anion. This study shows that F is the best candidate as it increases average voltage (voltage retention 96–97% after 200 cycles at 0.5 C), improves ionic conductivity (nearly two times higher than pristine), reduces cation mixing, minimizes oxygen release, and offers high stability during high temperature cycle. However, for S and Cl, the results are conflicted. An optimal amount of anion dopants should be considered as the side effects might overcome the benefits when the doping amount is excessive.

Unveiling the Influence of Carbon Impurity on Recovered NCM622 Cathode Material

“…With the carbon impurity, the valence of the transition metals at the particle surface is apt to be lower than that of the virgin cathode, which is likely caused by the reducibility of the carbon impurity that prevents further oxidation of transition metal ions during cathode formation. In addition, ions with lower oxidation states have larger sizes (for Co 2+ , R = 0.65 Å, while for Co 3+ , R = 0.545 Å) as well as weaker cohesion within the MO 2 layer, leading to the widening of lattice parameters, which matches the results discussed above. ,, More importantly, the large difference in ionic size and charge between Li + and Co 3+ ions results in good cation ordering, which is critical to support fast two-dimensional Li + diffusion and conductivity in the lithium layer. Thus, the increase of carbon impurity leads to a higher surface Co 2+ concentration that will further undermine the cathode electrochemical performance.…”

“…On the other hand, cathodes with a central cavity might exhibit good rate capability because of the reduced diffusion distances for Li + ions. Additionally, it has been reported that the void center could buffer the volume change during repeated lithium insertion/extraction, which suppresses the formation of intergranular cracks and leads to improved cyclability. − Therefore, this evidence suggests that the carbon impurity brings both positive and negative impacts on the cathode materials.…”

Cobalt‐Free Cathode Materials: Families and their Prospects

“…[ 211 ] In addition to the above‐mentioned metal ions, anions are also possible dopants, among which F is the most attractive element because it exhibits a two‐fold increase in the ionic conductivity of modified LMROs while improving the structural stability, especially at high temperature; moreover, the use of F provides good voltage retention of up to ≈96% at 0.5C after 200 cycles. [ 212 ] It has been also reported that F ‐ can prevent the compound from undergoing too much oxygen redox, which can trigger oxygen loss. [ 213 ] By the same token, Lee et al.…”

Challenges of layer-structured cathodes for sodium-ion batteries

“…Doping different anions (such as F À , Cl À , and S xÀ ) has been put forward as another approach to tailor the cathode materials in LIBs. 77 Li et al 78 demonstrated the feasibility that anions (ClO 4…”

“…Doping different anions (such as F − , Cl − , and S x − ) has been put forward as another approach to tailor the cathode materials in LIBs. 77 Li et al 78 demonstrated the feasibility that anions (ClO 4 − ) and cations (Na + ) could be co-(de)inserted in a layered structure oxide. It was first studied in a P3 phase Na 0.5 Ni 0.25 Mn 0.75 O 2 layered structure material.…”