Effects of cathode impedance on the performances of power-oriented lithium ion batteries

Abstract

Since power batteries have different requirements than traditional energy-oriented lithium ion batteries (LIBs) and their design concept is also different than energy-type cells, some new problems not encountered in energy-oriented LIBs must be carefully considered. This study illustrates that cathode impedance, a contributor to total cell impedance which can be ignored in the traditional energy-type LIBs, plays a very important role in power cells. This study uses 18650 cylindrical power cells consisting of a LiMn 2 O 4 cathode and graphite anode with a basic electrolyte of PC/EC/DMC = 1/3/6 by weight containing 1.2 M LiPF 6 as model power LIBs. This study also investigates the charge-discharge performance of these model batteries made from cathodes with the same recipe but dried at different oven temperatures. The high impedance cathode produced under a high drying temperature causes the cell to fail during high-power applications. Cell heating during extreme high rate discharging periods not only causes pore closure in the porous separator, but also cathode peeling from the substrate. These phenomena, increasing the cell resistance and reducing the transfer rate of charged species, are believed to be the main causes for the poor cycle life of model batteries in high rate discharge tests.

Elucidating the Driving Force of Relaxation of Reaction Distribution in LiCoO2 and LiFePO4 Electrodes Using X-ray Absorption Spectroscopy

“…These electrodes are typically composed of an active material, a conducting carbon, and a binder. The main resistive components in the composite electrodes are the electronic resistivity ( R el ), the ionic resistivities of the solid ( R ion(s) ) and liquid ( R ion(l) ) phases, and the ion transfer resistivity at the electrode/electrolyte interface ( R int ), − as shown in Figure . The resistivity is greatly influenced by the distribution of the components in the electrode and electrolytes (internal factors) as well as the operating conditions such as the charge/discharge rate and temperature (external factors) .…”

“…The reaction distribution in composite electrodes has been analyzed previously using modeling simulations. − Direct observations of the reaction distribution in composite electrodes with a micrometer-level spatial resolution have been reported only recently. Liu et al observed the inhomogeneous reaction in a LiFePO 4 composite electrode using microbeam X-ray diffraction (XRD) .…”

Comparison of Lithium-Ion Battery Cathode Materials and the Internal Stress Development

“…In current EV/HEV/PHEV markets, LiMn 2 O 4 is adopted as cathode materials for Li-ion batteries [46]. LiMn 2 O 4 cathode materials provide higher voltage than other materials, but its usage is limited by its short cycle life [15,47,48]. It is observed that the accelerated aging/degradation of LiMn 2 O 4 cathode materials is due to the dissolution of Mn in electrolyte under various charging voltage: with a higher charging voltage than 4.2V or nearly fully discharged.…”

Carbon-Binder Migration: A Three-Dimensional Evaporation Model for Lithium Ion Batteries

“…18,23 The main reason of migration seems to be convective and capillary forces developed during drying, while diffusion tend to re-homogenize the system. Fast drying and additive migration is typically detrimental for the final electrochemical performance and battery cycle life, [28][29][30] promoting electrode cracking (particularly severe for the case of thick electrodes and water processing), 31,32 poorly interconnected heterogeneous electrode mesostructures 23,24 and poor adhesion to the current collector. 18,29 From a computational perspective, the physical complexity of solvent evaporation in high SC dispersions makes challenging the development of devoted physics-based models.…”