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We present here a complete model of a Sony 18650HC lithium-ion battery developed in MATLAB/Simulink, which is adaptable to other lithium-ion cell chemistries and can be implemented into a full power system model. The model accounts for varying current rates, temperature dependencies and internal cell characteristics under both charge and discharge conditions and is primarily based on characterisation tests of the 18650HC cell with the addition of standard thermal equations and electrical relationships. The model can be adapted to fit other types of lithium-ion cell chemistries when the characterisation profile for that chemistry is created using our testing procedures. Comparisons between the model and experiments conducted on test cells have shown very accurate results and the adaptability of the model has been proven. This allows us to test and model newer cell technologies for which commercial data may not yet be available.

Advances in Li-ion technology mean that manufacturers currently produce cells that have higher energy densities, higher rate capabilities, and longer quoted cycle lives than the currently qualified ABSL space cells. It is therefore possible that cells are available that could enable a lower mass/volume solution for a given application.ABSL carry out regular reviews of commercial off the shelf (COTS) cells, to determine whether any available cells are suitable for space applications, and offer superior performance to those currently qualified. This paper describes the process that is followed to review and test commercial cells. INTRODUCTIONABSL has used the 18650HC(M) for space batteries since 1998; it was employed on the first ever Li-ion space battery for the PROBA-1 mission. Although the detailed performance and life-time characteristics of these cells are very well understood, advances in Li-ion technology mean that manufacturers currently produce cells that have double the energy density of this heritage cell. In addition, cells are available with the same energy density as the HC(M) but with considerably higher rate capabilities. Cells with longer cycle life have also been developed, although there is normally a trade-off in energy density such that a simple comparison cannot be made for end-of-life (EoL) performance.To date, ABSL have qualified three Li-ion cells for space applications, these are:x 18650HC(M). The heritage ABSL cell has a nominal capacity of 1.5Ah (133 Wh/kg) and has been extensively characterised. The design was modified in 2009 to include a central mandrel; this was to ensure a clear vent path in the case of overpressure. The cell was completely re-qualified following this change. x 18650HR. This cell was qualified specifically for a launch vehicle program and later adopted for MARES on the ISS. The cell has lower capacity than the HC(M) cell, but can deliver significantly higher currents. x 18650NL. This cell provides a considerable increase in energy density compared to the HC(M) cell: 189 Wh/kg compared to 133 Wh/kg. COTS cells have been recently assessed to identify those that may provide a performance benefit compared to the currently qualified cells. Due to the long durations for full qualification, and the quantity of life test data required to predict the long term performance, these reviews are carried out regularly. REVIEW PROCESSThe initial stage of any COTS assessment is to determine what cells are available on the market. During the last market survey, cells from over 40 companies were assessed. For this review, a commercially available database was used for the initial search [1]. The database was used to filter the available cells by chemistry and form factor; these were then ranked by performance requirements, e.g. energy density and cycle life.Once the initial list of cells was acquired from the database, the cell specification sheets were obtained. The data from these sheets were then assessed in detail against the cell performance requirements described below....

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