Li-rich cathode materials can offer a high specific capacity of ≥250 mA h g −1 ; however, the major issues are their structural instability, capacity degradation, and voltage decay upon prolonged cycling. Herein, we have shown that an increase in Ni content with a concomitant reduction in Mn and Co content in Li-rich cathode materials can help to alleviate structural and electrochemical instability to a considerable extent. In this regard, we have carried out a systematic investigation of tuning the Ni, Mn, and Co (NMC) content in the Li-rich phase, Li 1.2 (Ni x Mn y Co z )O 2 (where x + y + z = 0.8). In the composite notion, these Li-rich phases can also be written as 0.4(LiNi x Mn y Co z O 2 )•0.4(Li 2 MnO 3 ), where the layered oxide components LiNi x Mn y Co z O 2 (x + y + z = 1) are generally termed as NMC-333, NMC-442, NMC-532, NMC-622, and NMC-811, depending upon the concentration of metal constituents. The electrochemical studies reveal that the higher Ni-containing phase 0.4(LiNi 0.8 Mn 0.1 Co 0.1 O 2 )•0.4(Li 2 MnO 3 ) or Li 1.2 Ni 0.32 Co 0.04 Mn 0.44 O 2 shows the least voltage decay of about 0.4 V and a higher capacity retention of 85% after 100 cycles compared to those of the low Ni-containing composition 0.4(LiNi 0.33 Mn 0.33 Co 0.33 O 2 )•0.4(Li 2 MnO 3 ) or Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O 2 , which shows a higher voltage decay of 1.0 V with a 69% capacity retention after 100 cycles at a 0.2 C rate.

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There are ongoing efforts to improve the energy density of current day Li-ion batteries by using alloy-based anodes such as Si, Sn, or SnO 2 in place of graphite. Here we report template-assisted synthesis of Sn@C microspheres and SnO 2 @C microbowls prepared by phloroglucinol (P) − formaldehyde (F) gel method. The structural and morphological characterizations are carried out using XRD, FESEM, and HR-TEM. The electrochemical performance of SnO 2 @C as anode for Li-ion battery is investigated through cyclic voltammetry (CV) and galvanostatic charge-discharge cycling. At 1C rate, SnO 2 @C delivers a discharge capacity of 651 mA h g −1 over 150 cycles. Even at 5C rate, a reversible capacity of 494 mA h g −1 is observed with 72% of capacity retention over 200 cycles. Electrochemical impedance measurements also infer faster Li-ion transport kinetics in the electrode material. The postmortem FESEM images on electrochemically cycled material show that porous hollow structure is retained even after prolonged cycling. For comparison, the Li storage property of Sn@C microspheres (MS) tested as anode for Li-ion battery applications. This Sn@C composite delivered an excellent cycling capacity of 636 mA h g −1 at 1C rate over 400 cycles. When cycled at higher rate 5C, Sn@C composite exhibits high reversible capacity of 257 mA h g −1 with 68% of capacity retention over 250 cycles. These results highlight that combination of hollow architecture and porous carbon matrix of Sn@C and SnO 2 @C electrode provides better mechanical support to alleviate volume expansion issue of Sn electrode. K E Y W O R D S anode, Li-ion battery, Sn@C microspheres, SnO 2 @C micro bowls, volume expansion 1 | INTRODUCTION To minimize emission from vehicles and reduce pollution, there is paradigm shift to utilize renewable sources for energy generation and store it in batteries. 1-3 Lithium-ion batteries are the most promising energy storage systems for portable devices, automobile, and grid applications due to their high energy density, low weight and low self-discharge. 2-4 Current day Li-ion batteries use graphite as the anode, 5,6 which has limitations in terms of rate capability and suffers from Li-dendrite formation at high charge-discharge rates. 7,8 Therefore extensive efforts have been focused to replace the currently used graphite with alloy-based materials (Si or Sn