Nonlinear Conductivities and Electrochemical Performances of LiNi_0.5Co_0.2Mn_0.3O₂Electrodes

Abstract

There is increasing research attention on optimizing the carbon black nanoparticles' structure and loading procedure for improving conductivities and thus, electrochemical performances of cathodes in lithium-ion batteries. Recently, LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NCM523) has been actively investigated due to its larger specific capacity and lower cost compared to conventional cathode materials. Presented here is a high energy density NCM523 cathode obtained by reducing the carbon content using the state-of-the-art carbon nanoparticles developed at Cabot Corporation. It is the first time that the nonlinear conductivity of NCM523 electrodes has been discovered, which is significantly impacted by the dispersion and surface crystalline quality of carbon black nanoparticles, especially when the loading of carbon black is only 1 wt%. The nonlinear conductivity of the cathodes can dramatically affect their electrochemical performances at high rates ( 3C), which is close to the tunneling saturated current. In addition, there is no discernable difference in terms of the rate and cycle performance of the NCM523 electrodes, when reducing the loading of novel carbon black nanoparticles from 5 wt% to 1 wt% in the cathode. Therefore, the energy density of the electrode can be increased by 9% by using existing commercially available electrode materials. In lithium-ion batteries, the active materials of the cathodes typically exhibit relatively high resistivity due to their intrinsically poor electronic conductivity and the limited point contacts between their micro particles. [1][2][3][4][5][6] In addition, the active materials need to be mixed with binders to form the electrode, which insures the mechanical integrity and stability of the electrode. However, the binders are electric insulators that can further reduce the electrical conductivity of the electrode. To minimize the problem of the poor electrical conductivity of the electrode, conductive powders, such as carbon black, carbon fiber, carbon nanotube, or graphene, are added to the electrode formulation. [5][6][7][8][9][10] In the battery industry, there are at least two competing requirements for the amount of conductive additive needed: (i) high rate performance requiring a large amount of conductive additive and (ii) high energy density dictating that the amount of conductive additive be as low as possible. These two antagonistic requirements make high demands on optimizing conductive additives as the solution. 5,6,8,10 Meanwhile, the cost is always critical for the commercial application of carbon additives. Therefore, there is increasing research attention on the carbon black nanoparticles, since it is the cheapest one among a series of carbon additives. The research focuses on the impacts of their structures, the pretreatment and loading procedures on the cathodes' performances, etc. 5,6,[10][11][12][13][14] The mechanism for the electronic conduction of carbon black nanoparticles' aggregates in cathodes is believed to occur through tunneling phenomena, the probabil...

Charge Transport in Single NCM Cathode Active Material Particles for Lithium-Ion Batteries Studied under Well-Defined Contact Conditions

“…Such approaches yield easy access to effective characteristics of the composite as a whole, e.g., specific energy density, capacity retention, or cycle lifetime. However, as the interplay of material components and the microstructure of the composite electrode determine its effective properties, − the individual contributions of its components or of interfaces and interphases formed between them cannot be easily separated. Little can be learned about the intrinsic properties of the CAM within the composite electrode, e.g., effects of size of primary and secondary CAM particles or of network formation.…”

Prediction Clue on the Fading Capacity of Multi-Walled Carbon Nanotube-Decorated Li2(Fe1–xTix)SiO4/C High-Performance Cathode Materials

“…The intensity ratios of I D / I G are calculated as 1.051, 1.008, 0.899, 0.869, and 0.852 for LFS/C; LFTS/C; and 2.5, 5, and 10 wt % of MWCNT-added LFTS/C nanocomposites, respectively. The effective carbon content that can contribute to enhance the electrochemical behavior of the sample mainly depends on the graphitized carbon or the crystallized content of carbon within the active sample. , The crystallized carbon contents of all the samples have been calculated using the integral area within the D and G bands of Raman spectra using the relation crystalline carbon content (in %) = A (G)/( A (G) + A (D)), where A (D) and A (G) are the integral areas within the D and G bands, respectively [Figure (ii)­(a–e)]. The calculated crystalline percentages of carbon for all the samples are tabulated in Table S2.…”

Enhanced Raman Scattering from NCM523 Cathodes Coated with Electrochemically Deposited Gold

“…This region of the spectrum typically contains the G-band and D-band contributions from disordered graphitic material. 1,9,12,13 By adopting the above described normalization procedure (i.e., using the BaF 2 phonon as an internal standard) and comparing peak-to-baseline intensity values for the averaged uncoated and goldcoated map spectra, the average intensity of the NCM523 Raman scattering from the gold-coated region is found to be enhanced by a factor of ca. 20 compared to the average scattering from the uncoated region.…”

“…[4][5][6][7] The mixed transition metal oxide LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NCM523) is a well-studied member of the Li-Ni-Co-Mn-O (NCM) class of materials employed as cathodes in lithium-based batteries. [8][9][10][11][12][13][14] Raman measurements can be made on NCM phases in powder form but the most useful information is gained from studies of NCM cathode laminates-before, during, and after electrochemical cycling. In some cases (in particular for the Ni-rich NCM phases) the Raman scattering from the NCM phase phonons is weak and also quite variable from sample to sample.…”