Power-assist Hybrid Electric Vehicle Research Articles

Non-Isothermal Aging of Lithium-Ion Cells

Lithium-ion batteries are rapidly being adopted for transportation applications, ranging from hybrid- to full-electric vehicles. To assure that the automotive battery can meet the demands of these applications, the US Advanced Battery Consortium has established test manuals and performance targets for each application [1-3]. These manuals use accelerated tests to gather needed performance degradation information in a limited amount of time. Models are then developed from these data that relate performance decline to the magnitude and duration of the stress. Isothermal aging stresses the battery under a simple set of conditions and can be used to elucidate the underlying degradation mechanisms. It is then generally assumed that a cumulative degradation model of aging under non-isothermal conditions would be a linear combination of the isothermal results. However, this approach may not directly predict the non-isothermal behavior. A model based on degradation rates may be a better predictor. In theory, integrating the rate-based model over the temperature path can then express the cumulative degradation. The results of this investigation will be discussed. The work at Argonne National Laboratory was performed under the auspices of the U.S Department of Energy (DOE), Office of Vehicle Technologies, under Contract No. DE-AC02-06CH11357. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. The efforts at Idaho National Laboratory and at Lawrence Berkeley National Laboratory were performed under Contract Numbers DE-AC07-05ID14517 and DE-AC03-76SF00098, respectively.This article issue has been created by UChicago Argonne, LLC, Operator of Argonne National Laboratory (Argonne). Argonne, a DOE Office of Science Laboratory, is operated under Contract No. DE-AC02-06CH11357. The U.S. Government retains for itself, and others acting on its behalf, a paid-up, nonexclusive, irrevocable, worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government. References FreedomCAR Battery Test Manual for Power-Assist Hybrid Electric Vehicles, DOE/ID-11069, October 2003.Battery Test Manual for Plug-In Hybrid Electric Vehicles, Rev. 3, INL/EXT-14-32849, September 2014.Battery Test Manual for Electric Vehicles, INL/EXT-15-34184, Rev. 3, June 2015

Safe lithium-ion battery with ionic liquid-based electrolyte for hybrid electric vehicles

A lithium-ion battery featuring graphite anode, LiFePO4-C cathode and an innovative, safe, ionic liquid-based electrolyte, was assembled and characterized in terms of specific energy and power after the USABC-DOE protocol for power-assist hybrid electric vehicle (HEV) application. The test results show that the battery surpasses the energy and power goals stated by USABC-DOE and, hence, this safe lithium-ion battery should be suitable for application in the evolving HEV market.

Fast sol–gel synthesis of LiFePO4/C for high power lithium-ion batteries for hybrid electric vehicle application

LiFePO4/C of high purity grade was successfully synthesized by microwave accelerated sol–gel synthesis and showed excellent electrochemical performance in terms of specific capacity and stability. This cathode material was characterized in battery configuration with a graphite counter electrode by USABC–DOE tests for power-assist hybrid electric vehicle. It yielded a non-conventional Ragone plot that represents complexity of battery functioning in power-assist HEV and shows that the pulse power capability and available energy of such a battery surpasses the DOE goal for such an application.

The UltraBattery—A new battery design for a new beginning in hybrid electric vehicle energy storage

The UltraBattery, developed by CSIRO Energy Technology in Australia, is a hybrid energy storage device which combines an asymmetric super-capacitor and a lead–acid battery in single unit cells. This takes the best from both technologies without the need for extra, expensive electronic controls. The capacitor enhances the power and lifespan of the lead–acid battery as it acts as a buffer during high-rate discharging and charging, thus enabling it to provide and absorb charge rapidly during vehicle acceleration and braking. The initial performance of the prototype UltraBatteries was evaluated according to the US FreedomCAR targets and was shown to meet or exceed these in terms of power, available energy, cold cranking and self-discharge set for both minimum and maximum power-assist hybrid electric vehicles (HEVs). Other laboratory cycling tests showed a fourfold improvement over previous state-of-the-art lead–acid batteries under the RHOLAB test profile and better life than commercial nickel/metal hydride (NiMH) cells used in a Honda Insight when tested under the EUCAR HEV profile. As a result of this work, a set of twelve 12 V modules was built by The Furukawa Battery Co., Ltd. in Japan and were fitted into a Honda Insight instead of the NiMH battery by Provector Ltd. The battery pack was fitted with full monitoring and control capabilities and the car was tested at Millbrook Proving Ground under a General Motors road test simulation cycle for an initial target of 50 000 miles which was extended to 100 000 miles. This was completed on 15th January 2008 without any battery problems. Furthermore, the whole test was completed without the need for any conditioning or equalisation of the battery pack.

Consequences of including carbon in the negative plates of Valve-regulated Lead–Acid batteries exposed to high-rate partial-state-of-charge operation

In power-assist hybrid electric vehicles (HEVs) batteries are required to operate from a partial-state-of-charge baseline and to provide, and to accept, charge, for short periods, at very high rates. Under this regime conventional lead–acid batteries accumulate lead sulfate on the negative plate and fail quickly. This failure mode can be effectively countered by the inclusion of certain forms of carbon at greater concentrations than have been used in lead–acid batteries in the past. So effective is this preventive measure that VRLA batteries benefiting from the inclusion of such carbon have been able to substitute for nickel metal hydride batteries in power-assist HEVs with no significant loss of performance. There has been much speculation about the function of the carbon that is providing this remarkable improvement. This paper aims to review the several mechanisms that have been proposed as possibly playing some contributory role.

Correlation of Arrhenius behaviors in power and capacity fades with cell impedance and heat generation in cylindrical lithium-ion cells

A series of cylindrical 18650 lithium-ion cells with an MAG-10|1.2 M LiPF 6 ethylene carbonate (EC):ethyl methyl carbonate (EMC) (w:w=3:7)|Li x Ni 0.8Co 0.15Al 0.05O 2 configuration were made and tested for power-assist hybrid electric vehicle (HEV) applications under various aging conditions of temperature and state-of-charge (SOC). The cells were intermittently characterized for changes in power capability, rate capacity, and impedance as aging progressed. The changes of these properties with temperature, as depicted by Arrhenius equations, were analyzed. We found that the degradation in power and capacity fade seems to relate to the impedance increase in the cell. The degradation follows a multi-stage process. The initial stage of degradation has an activation energy of the order of 50–55 kJ/mol, as derived from power fade and C 1 capacity fade measured at C/1 rate. In addition, microcalorimetry was performed on two separate unaged cells at 80% SOC at various temperatures to measure static heat generation in the cells. We found that the static heat generation has an activation energy of the order of 48–55 kJ/mol, similar to those derived from power and C 1 capacity fade. The correspondence in the magnitude of the activation energy suggests that the power and C 1 capacity fades were related to the changes of the impedance in the cells, most likely via the same fading mechanism. The fading mechanism seemed to be related to the static heat generation of the cell.