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6 Power Technology of Lunar Lander
(2) Lithium-ion battery pack
The electrical performance of lithium-ion battery pack was closely related to temperature. Especially under low temperature and high temperature environments, the
electrical performance of lithium-ion battery pack would degrade rapidly and might
even fail. At low temperature, when the charging current was large, many lithium
ions would migrate to the negative electrode surface. Due to the slow diffusion rate
of lithium ions and low ion permeability of the Solid Electrolyte Interphase (SEI)
film (as a negative electrode protection) at low temperature, part of lithium ions did
not diffuse through the SEI film but were deposited directly on the negative electrode
surface, resulting in the production of metallic lithium. Lithium might interact with
the electrolyte easily to generate gas or form lithium dendrites which would penetrate
the separator to cause a short circuit in the battery.
At high temperatures, the performance of SEI film is unstable and prone to decomposition. The newly exposed carbon negative electrode will consume a portion of
lithium and form new SEI film on the surface, resulting in irreversible capacity loss
of the cell. At the same time, the formation of the SEI film is usually accompanied
by gas generation, resulting in increase of internal pressure of the battery to increase
internal resistance of the battery.
3. Analysis of Lunar Dust Effect
After the lunar lander was landed on lunar surface, lunar dust was mainly activated
by engine plume on lunar surface during landing. Before landing, the solar array was
folded. After landing, there would be a certain period of time before the solar array
was deployed again, which could effectively prevent lunar dust from covering surface
of the solar array to pollute. In the phase of normal operation in lunar daytime, the
impact of lunar on solar cell power generation was compensated by retaining certain
margin of power output and adjusting the operation mode.
4. Analysis of Other Effects
Similar to nickel-cadmium battery in space application, lithium-ion battery uses lean
liquid and the electrolyte inside the battery cell is completely absorbed in the separator
and the pole pieces. There is no free electrolyte inside. It was necessary to analyze
whether 1/6 g gravity had an effect on the normal operation of lithium-ion battery
pack. The lunar eclipse will occur during the lunar daytime. During such period,
the lunar lander load would be completely provided by the battery pack. Therefore,
the discharge capacity of the battery pack should be evaluated to design a suitable
operation mode in lunar eclipse to ensure the power supply safety.
If the nominal lifetime of the lunar lander on lunar surface was one year, it would
pass 12 lunar nights. Every lunar night lasts for 14 earth days. During lunar night,
there is no sunlight and the solar array cannot generate electricity. If there was only
lithium-ion battery pack, it was impossible to provide continuous energy for such
long period of time. Therefore, all electric instruments should be shut down before the
lunar lander entered into lunar night. The battery discharge switch was disconnected
to make the lunar lander go into hibernation. When the lunar night was over, the
lunar lander would be awakened again. For detailed design, see Sect. 6.5.4.
6 Power Technology of Lunar Lander
(2) Lithium-ion battery pack
The electrical performance of lithium-ion battery pack was closely related to temperature. Especially under low temperature and high temperature environments, the
electrical performance of lithium-ion battery pack would degrade rapidly and might
even fail. At low temperature, when the charging current was large, many lithium
ions would migrate to the negative electrode surface. Due to the slow diffusion rate
of lithium ions and low ion permeability of the Solid Electrolyte Interphase (SEI)
film (as a negative electrode protection) at low temperature, part of lithium ions did
not diffuse through the SEI film but were deposited directly on the negative electrode
surface, resulting in the production of metallic lithium. Lithium might interact with
the electrolyte easily to generate gas or form lithium dendrites which would penetrate
the separator to cause a short circuit in the battery.
At high temperatures, the performance of SEI film is unstable and prone to decomposition. The newly exposed carbon negative electrode will consume a portion of
lithium and form new SEI film on the surface, resulting in irreversible capacity loss
of the cell. At the same time, the formation of the SEI film is usually accompanied
by gas generation, resulting in increase of internal pressure of the battery to increase
internal resistance of the battery.
3. Analysis of Lunar Dust Effect
After the lunar lander was landed on lunar surface, lunar dust was mainly activated
by engine plume on lunar surface during landing. Before landing, the solar array was
folded. After landing, there would be a certain period of time before the solar array
was deployed again, which could effectively prevent lunar dust from covering surface
of the solar array to pollute. In the phase of normal operation in lunar daytime, the
impact of lunar on solar cell power generation was compensated by retaining certain
margin of power output and adjusting the operation mode.
4. Analysis of Other Effects
Similar to nickel-cadmium battery in space application, lithium-ion battery uses lean
liquid and the electrolyte inside the battery cell is completely absorbed in the separator
and the pole pieces. There is no free electrolyte inside. It was necessary to analyze
whether 1/6 g gravity had an effect on the normal operation of lithium-ion battery
pack. The lunar eclipse will occur during the lunar daytime. During such period,
the lunar lander load would be completely provided by the battery pack. Therefore,
the discharge capacity of the battery pack should be evaluated to design a suitable
operation mode in lunar eclipse to ensure the power supply safety.
If the nominal lifetime of the lunar lander on lunar surface was one year, it would
pass 12 lunar nights. Every lunar night lasts for 14 earth days. During lunar night,
there is no sunlight and the solar array cannot generate electricity. If there was only
lithium-ion battery pack, it was impossible to provide continuous energy for such
long period of time. Therefore, all electric instruments should be shut down before the
lunar lander entered into lunar night. The battery discharge switch was disconnected
to make the lunar lander go into hibernation. When the lunar night was over, the
lunar lander would be awakened again. For detailed design, see Sect. 6.5.4.