Elsevier

Journal of Power Sources

Volume 266, 15 November 2014, Pages 170-174
Journal of Power Sources

Short communication
Characterization tests for plug-in hybrid electric vehicle application of graphite/LiNi0.4Mn1.6O4 cells with two different separators and electrolytes

https://doi.org/10.1016/j.jpowsour.2014.05.016Get rights and content

Highlights

  • Graphite/LNMO cells were tested by protocol for plug-in HEV application.

  • Cell assemblies with two different separators were tested in two electrolytes.

  • PVdF-based separator had strong impact on high-rate functioning LIB for PHEVs.

Abstract

The paper reports and discusses the results of electrochemical tests carried out according to the DOE Battery Test Manual for plug-in Hybrid Electric Vehicles (PHEVs) on laboratory high-voltage graphite/LiNi0.4Mn1.6O4 cells with electrode formulation and mass-loading suitable for scale-up, and mixed ethylene carbonate–dimethyl carbonate with two diverse lithium salts, lithium tris(pentafluoroethyl)trifluorophosphate and LiPF6, as electrolytes. The cells, assembled with two different separators, a polypropylene monolayer separator (Celgard®2400) and a reinforced polyvinylidene fluoride macroporous membrane (PVdF-NCC), were also tested by deep charge/discharge cycles. The results show the strong impact of the separator on high-rate cell functioning in PHEVs.

Introduction

The worldwide demand for clean, low-fuel-consuming transport has promoted the development of safe, high-energy and power lithium-ion batteries for hybrid electric vehicles (HEVs) in the last ten years. The performance requirement for the battery system depends on the level of power-train hybridization and on the range of the electric driving. Power-assist HEVs with optimized fuel consumption and a short electric driving range are already marketed by several car manufacturers [1]. In power-assist HEVs the battery system operates in charge-sustaining (CS) mode via a dynamic functioning with shallow charge–discharge cycles around a constant state of charge. The battery discharges to provide extra power during vehicle acceleration and recovers energy from regenerative braking or from the internal combustion engine.

The electric driving range in the plug-in HEVs (PHEVs) is greater than in power-assist HEVs. The energy to drive the vehicle also comes from the battery which is recharged by the electric-grid. There are two battery operation modes: i) charge-depleting (CD) with a net decrease of the state of charge during electric propulsion of the vehicle, and ii) charge-sustaining (CS), which is similar to that of the power-assist HEV. While the power demand for the battery systems is thus almost the same for HEVs and PHEVs, the energy needed by the latter, which also operates in depleting-mode, is significantly higher. The power-to-energy ratio targets set by US Department of Energy (DOE) are 13 for minimum PHEV and 83 for minimum power-assist HEV [2], [3]. Although high-energy battery pack is an issue that is still under study as well as battery safety and costs, and high-voltage lithium-ion batteries of different chemistry are under investigation, some PHEVs are already on the market.

High-voltage graphite/LiNi0.4Mn1.6O4 cells with reinforced polyvinylidene fluoride macroporous separator (PVdF-NCC) were recently tested against cells with commercial polypropylene monolayer (Celgard®2400) according to FreedomCAR-DOE protocols for power-assist HEV [4], and several PVdF macroporous separators were investigated in high charge-rate Li4Ti5O12/LiMn2O4 cells and compared to commercial polyolefin separators [5].

The present paper reports and discusses the results of electrochemical tests carried out according to DOE protocols for PHEV application [3], as well as of deep charge/discharge cycles on graphite/LiNi0.4Mn1.6O4 cells featuring electrodes of optimized formulation and mass-loading suitable for scale-up of batteries for PHEV [6], two different separators (Celgard®2400 and PVdF-NCC) and ethylene carbonate–dimethyl carbonate with different lithium salts as electrolytes.

Section snippets

Experimental

Full cells were assembled with positive and negative electrodes prepared by pre-industrial pilot lines and provided by CEA-LITEN (Grenoble, France). Two assemblies were tested: one with a commercial polypropylene separators (Celgard®2400, 25 μm), and the other with polyvinylidene fluoride (PVdF)-nano crystalline cellulose (NCC) reinforced membranes (23–28 μm) prepared by a phase-inversion process [7] with 9–15% NCC content and provided by INP-LEPMI (Grenoble, France). Electrodes and separators

Results and discussion

Electrochemical tests by the FreedomCAR-DOE protocols for plug-in HEV application [3] were performed on graphite/LNMO cells with Celgard®2400 or PVdF-NCC separators. In the last few years PVdF-based separators have been the focus of much interest, as reviewed by Costa et al. in ref. [9], for their interesting properties like high dipolar moment, high dielectric constant, tailored porosity, chemical and electrochemical stability in cathodic environment and good contact with electrodes. PVdF-NCC

Conclusions

The results of the electrochemical tests on high-voltage laboratory graphite/LNMO cells with optimized electrode formulation and mass electrode loading suitable for scale-up of batteries for the high-energy demanding plug-in applications show the strong effect of the separator on cell performance. Unlike cells with Celgard®2400, which displayed usable energy values with satisfactory energy margin only for Minimum PHEV in LF30, cells with PVdF-NCC macroporous membrane displayed in both LF30

Acknowledgments

The "Advanced Fluorinated Materials for High Safety, Energy and Calendar Life Lithium Ion Batteries" (AMELIE) Project n. 265910 was funded by the 7th European Framework Programme (FP7-Transport). The authors thank L. Picard and G. Yildirim (CEA-LITEN), J.-Y. Sanchez, F. Alloin and M. Bolloli (INPG-LEPMI) for providing some cell components, all the Project Partners for the useful discussions and UE for financial support.

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