Prognostics for lithium-ion batteries using a two-phase gamma degradation process model.

To address the degradation of rechargeable batteries, this paper presents a two-phase gamma process model with a fixed change-point for modeling the voltage-discharge curves of battery cycle aging under a constant current. The model can be applied to estimate the state of charge (SOC) and the remaining useful discharge time (RUT) in a cycle with consideration of the effect of cycle aging, and can also be applied to estimate the state of life (SOL) and the remaining useful life (RUL) across cycles. The applications of the proposed model are demonstrated using the experimental cycle aging data of a lithium iron phosphate battery. A comparison shows that the proposed model generates a more accurate prediction than the conventional two-term exponential model with capacity data under a particle filter framework, and this reveals the superiority of modeling with voltage over modeling with capacity. The analytical expression of mean useful discharge time in a cycle (or mean time to failure) is developed with approximation by a Taylor expansion and the Birnbaum-Saunders distribution, and the result is shown to be in good agreement with the true mean of a gamma process.

Nanostructured porous manganese carbonate spheres with capacitive effects on the high lithium storage capability.

In this paper, nanostructured porous MnCO3 spheres are facilely synthesized, which can simultaneously provide an increased surface for conversion reaction and capacitive storage as the anode material for lithium ion batteries. This material gives a superior specific capacity and excellent long-term cycling performance even at a high current density. It can deliver a stable capacity of 1049 mA h g(-1) after 200 cycles at a current density of 1000 mA g(-1), which is much higher than the theoretical capacity of 466 mA h g(-1). After 2000 cycles at a high current density of 5000 mA g(-1), a capacity of 510 mA h g(-1) can still be maintained. Their high rating performance at 5000 mA g(-1) is among the best-reported performances of anode materials. From the in situ or ex situ SEM observation, the porous MnCO3 nanostructure can provide a stable template for reversible lithium insertion and extraction without significant morphology change and accommodate the volume change during the charge-discharge process. Also this structure increases the capacitive contribution to the total capacity compared with other MnCO3 samples.