A facile and generic method to improve cathode materials for lithium-ion batteries via utilizing nanoscale surface amorphous films of self-regulating thickness

Abstract

As a facile and generic surface modification method, a unique class of surface amorphous films (SAFs) is utilized to significantly improve the rate performance and cycling stability of cathode materials for lithium-ion batteries. These nanoscale SAFs form spontaneously and uniformly upon mixing and annealing at a thermodynamic equilibrium, and they exhibit self-regulating or "equilibrium" thickness due to a balance of attractive and repulsive interfacial interactions acting on the films. Especially, spontaneous formation of nanoscale Li3PO4-based SAFs has been demonstrated in two proof-of-concept systems, LiCoO2 and LiMn1.5Ni0.5O4, which have an equilibrium thickness of ∼2.9 nm and ∼2.5 nm, respectively. At a high discharge rate of 25 C, these Li3PO4-based SAFs improve the discharge capacity by ∼130% for LiCoO2 and by ∼40% for LiMn1.5Ni0.5O4, respectively. Furthermore, these SAFs improve the cycling stability and reduce capacity fading of both LiCoO2 and LiMn1.5Ni0.5O4. At an elevated temperature of 55 °C, Li3PO4-based SAFs can help to maintain ∼90 mA h g(-1) discharge capacity of the high-voltage material LiMn1.5Ni0.5O4 after 350 cycles at a relatively high charge-discharge rate of 1 C. Further mechanistic studies suggest that these SAFs reduce the interfacial charge transfer resistance and suppress the growth of the solid-electrolyte interphase. This facile method can be utilized to improve a broad range of cathode and anode materials. A thermodynamic framework is proposed, which can be used to guide future experiments of other material systems.

Communication—Enhancing the Electrochemical Performance of Lithium-Excess Layered Oxide Li1.13Ni0.3Mn0.57O2 via a Facile Nanoscale Surface Modification

“…Although the bulk structure of LP500 is retained, the temperature is not high enough to form an effective coating layer on the layered oxides. 10 Both LNMO and LP600 are cycled for extra 50 times. After 150 cycles, the capacity difference between the LNMO and LP600 increases to 49 mAh g −1 , which is larger than 36 mAh g −1 of the first cycle.…”

“…Both materials show larger charge/discharge capacities than their low current testing values at room temperature, which is due to the higher lithium activity at elevated temperature. 10 An obvious elongated slope (∼ 218 mAh g −1 ) appears in LNMO, which indicates the reactions between electrode and electrolyte happens below 4.4 V at 55…”

Operando Lithium Dynamics in the Li‐Rich Layered Oxide Cathode Material via Neutron Diffraction

“…[ 2,3 ] The lithium layered oxides utilize transition metal redox pairs for charge/ discharge compensation during lithium extraction and intercalation offering a theoretical capacity of 270 mAh g −1 for complete lithium extraction. [ 3,4 ] However, practical capacities have so far shown to be ≈200 mAh g −1 due to degradation reactions and large lattice contractions at low lithium content, limiting its capability to meet future demands. One possible cathode material is the Li-rich layered oxide compounds x Li 2 MnO 3 ⋅(1 − x )LiMO 2 (M = Ni, Mn, Co) (0.5 = < x = <1.0) that exhibit capacities over 280 mAh g −1 obtainable by the combination of the typical transition metal redox pair with the additional oxygen redox reaction as the charge compensation mechanism.…”

Composites of sodium manganese oxides with enhanced electrochemical performance for sodium-ion batteries: Tailoring properties via controlling microstructure

“…In this work, the Na 0.44 MnO 2 phase is clearly the majority phase for both specimens (Figure 2), whereas the excess amounts of Na (since the Na/Mn ratios were measured to be 0.60 for both specimens) lead to the formation of secondary layer-structured phases with higher Na contents, which may affect the electrochemical performance of the composite electrodes as discussed subsequently. It is also possible that some Na-rich amorphous phases may form during the high-energy ball milling and heat treatments, either as bulk secondary phases or as 2-D interfacial phases (nanoscale surface [14][15][16][17][18][19] or intergranular [15,18,20] "amorphous" films), as shown in prior studies of lithium-ion battery materials that were made by similar ball milling and annealing processes [15][16][17][18][19].…”

“…The high rate capabilities of specimen B represented another example of the so-called "synergistic effect" that was observed in layered P-and O-type composites [8,9]. It is also possible that rate capabilities were improved by the formation of amorphous-like 2-D surface phases that often form spontaneously in ball-milled and annealed materials [15][16][17][18][19]. Future investigation should be conducted to probe the exact mechanisms for the improved rate capabilities.…”