![]() 13–15 The structural stability is likely to be improved by Mn 4+, which is electrochemically inactive. 11,12 Mn is involved in the structural and thermal stability of the NMC cathode material. 9,10 Also, the presence of Co 3+ may suppress structural distortion resulting from the Jahn–Teller effect of Ni 3+. 7,8 Co can partially contribute to capacity achievement, but mostly it improves the rate capability of the battery. Ni is the key element that enables high capacity of the battery by a two-stage redox reaction between Ni 2+/Ni 3+ and Ni 3+/Ni 4+. 4–6 In addition, cathodes containing mixed transition metals of Ni, Mn, and Co can provide synergic advantages over a single transition metal oxide cathode. 1–3 Since the last decade, attention has been paid to layered transition metal oxide batteries, which can be represented by the formula of LiNi xCo yMn 1− x− yO 2 (NMC, x > 0 and y > 0), owing to their high discharge capacity (<200 mA h g −1), high energy density, and lower cost compared to conventional LiBs ( e.g., LiCoO 2). Introduction Lithium-ion batteries (LiBs) have attracted great interest as an energy storage system for various applications ranging from mobile devices to electric vehicles and energy storage stations for solar cells. Energy level alignment itself is likely to be the key process that leads to the active formation of unstable CEI layers on charge–discharge. Hence, a downward band bending could be depicted based on the work function and the energy level difference between the Fermi level ( E F) and the valence band maximum ( E VBM). Negatively charged elements tend to be present at the close surface of the cathode, while the positively charged Li + migrates from the cathode to the CEI layer. Herein, we empirically identify the energy level band bending of a Ni-rich NMC cathode ( i.e., Li(Ni 0.5Mn 0.3Co 0.2)O 2) with the visual evidence of Li + transfer from the electrode to the CEI layer (adsorbate). The CEI layer consists of various by-products ( e.g., LiF, Li 2CO 3, ROLi, and ROCO 2Li (R: alkyl group)) decomposed from redox reactions between the cathode and the electrolyte, which can lead to dramatic capacity fading and stability issues. The analysis attributed electrochemical features from both species, including the high voltage profiles from the NMC and the good pulse performance from the LFP.Cathode–electrolyte interphase (CEI) formation between the cathode and the electrolyte is a critical factor that determines the stability of lithium-ion batteries (LiBs). The EIS analysis allowed cell kinetics and transfer mechanisms to be assigned and compared between the two chemistries. Blended cathodes were made with 70% NMC and 30% LFP. The coin cells tested had NMC, LFP, or a blend of NMC/LFP as the primary material in the cathode. This allows any performance effects from the anode to be eliminated. This experiment focused specifically on the cathode by assembling half-cells, which cycle the cathode against pure lithium. The research conducted focuses on testing cathode materials by performing electrochemical and rate testing followed by electrochemical impedance spectroscopy (EIS). For this reason, blends of NMC and LFP can impart the high energy density of NMC, with the safety and pulsed performance of LFP. Lithium-iron-phosphate (LFP) is less common due to its lower voltage range but exhibits higher safety and better high rate performance, especially during pulses of high current demand. Lithium-nickel-manganese-cobalt-oxide (NMC) is a favored cathode active material in EVs because of its high energy density and high voltage limits, with the challenge of inferior high rate performance than other chemistries. Their high power and energy capability provides power for small consumables, such as watches, up to electric vehicles (EVs) and grid scale energy storage systems. The need for renewable energy is rapidly increasing, and the optimization of lithium-ion batteries is critical for the industry. ![]()
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