SES 50Ah Lithium Metal Cell

SES 50Ah cell and discharge capacity curves at different temperatures

The SES 50Ah lithium metal cell specification sheet was released in December 2022 [1].

Included in our benchmarking as this shows a cutting edge cell technology for 2023.

However, at this point there are some questions as the data has some incomplete and missing parts. This will be described through the post where values are compared.

Key features

  • 357Wh/kg at C/10, 25°C
  • 773Wh/litre at C/10, 25°C
  • 1076W/kg
  • 2328W/litre

Designed to meet

  • Safety:
  • Transport: UN38.3
  • Quality:
  • Nominal Capacity = 50.7Ah at 25°C at C/10
  • Nominal Voltage 3.84V at C/10 at 25°C
  • Nominal Energy = 3.84V x 50.7Ah = 194.7Wh at C/10 at 25°C
  • Maximum charge = ?
  • Cutoff voltage = 2.5V
  • Maximum continuous discharge 150A
  • Maximum pulse discharge 160A and 586W 10s (also 2s, 5s and 30s)
  • Operating temperature range = -10°C to 45°C
  • Storage temperature range °C
  • Cycle life 95% capacity at 315 cycles (C/10 charge, C/3 discharge)
    • Linear extrapolation takes this to 1900 cycles at 70%

The datasheet for this cell does not explicitly give the nominal voltage. However, it does have a chart of OCV vs SOC and they give the discharge curves at different rates. From this we can digitally extract the nominal voltage for the cell at C/10.

The low charge rate for the cycle life testing is a concern and it would be good to see this at C/3 charge and C/3 discharge.

Dimensions

  • L: mm
  • W: mm
  • H: mm
  • Volume: 0.252litres
  • Mass: 0.545kg

The image (top of this page) of the cell main body is 68 x 347 pixels. Knowing this ratio and then fixing either the length or width of the cell allows us to calculate the other dimensions.

table of cell dimensions calculated from the image and Wh/litre value

Fixing the cell length at 350mm gives perhaps the most sensible dimensions.

We calculated the total energy in the cell and the datasheet gives the energy density values, hence we can calculated the mass and volume of the cell.

SES 50Ah cell fixture for testing

There is a caveat to all of the cell level dimensions and density values as the specification sheet does not declare the pressure required to maintain the cell performance.

The rig used in the safety tests shows very substantial plates and bolts used to clamp the cell.

Test data

  • Maximum discharge current = 150 to 160A
  • Short circuit current = 695A
  • ACIR
  • DCIR = 1.1mΩ 10s 2C pulse at 50% SoC and 25°C

Values are given in the specifications for 3C continuous discharge. A graph showing the external short circuit test gives the maximum current and then shows the steady discharge just above 3C. With the available data it would be best to give the maximum discharge current as 160A. As the internal resistance at 50% SoC is 1.1mΩ then the peak discharge power would be 584W

cell DCIR graph and table of values

The 10s pulse DCIR values are given in the datasheet. This graph has been digitised and the values shared here for clarity.

SES 50Ah

We took a set of data points through the continuous discharge curves. Thus allowing us to plot voltage versus current.

cell voltage versus current graph at continuous discharge rates for the SES 50Ah cell

The gradient of the line through these data points is Voltage/Current and hence the internal resistance of the cell.

This gives a value of 1.14mΩ for the internal resistance in continuous discharge.

This is a good value, but interesting that it is very close to the pulse discharge value.

This post has been built based on the support and sponsorship of: Quarto Technical ServicesTAE Power Solutionsh.e.l group and The Limiting Factor. 

Safety data

Independent safety tests of the cell.

Safety test results table for SES 50Ah cell

The safety tests are a good start, but lots of testing still to do.

data from cell nail penetration test

The nail penetration test result needs describing as the cell voltage remaining stable and no change in temperature raises concerns over the test.

cell voltage and temperature measurements during external heat test

The external heat test shows the impact of the cell clamping system. This has added a significant thermal mass and means that the cell never got to 130°C before it was removed and allowed to cool.

Also, the cell was only at an elevated temperature for a short time.

This test should be repeated such that the cell temperature reaching 130°C triggers the start of the 1 hour test.

Conclusions for SES 50Ah lithium metal cell

An interesting cell chemistry and a dataset that is 60% to being complete. However, a fully independent set of data is required to understand exactly what this cell is capable of. What this cell needs in terms of mechanical support and thermal control is difficult to ascertain from this datasheet.

Note: if you have tested this cell independently and able to share data please contact us nigel@batterydesign.net

References:

  1. SES 50Ah LiMetal Cell Data Report, SES, December 2022

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