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What is the Efficiency of Lithium-ion Batteries?

May. 30, 2022

What is the Efficiency of Lithium-ion Batteries?

Lithium-ion batteries were first introduced in the 1960s when Bell-Laps introduced a working graphite anode to provide an alternative to lithium batteries (lithium metal). The first commercial lithium-ion battery was produced by Sony. Since then, advanced material developments and technologies have led to significant and dramatic improvements in energy density and cycle life.

When it comes to the efficiency of lithium-ion batteries, it is almost 100%, which is the biggest advantage over other battery technologies on the market.

Lithium-ion batteries have a fast discharge and charge time constant, which is the time to reach 90% of the battery's rated power, of about 200ms, with a round-trip efficiency of up to 78% within 3500 cycles. It is well known that Li-ion batteries have become the most critical storage technology, especially in portable and mobile applications, such as e-bikes, cell phones, laptops, electronic cards, etc.

What really cripples lithium-ion batteries?

If you want to know what is destroying Li-ion batteries, then there are many factors. So, let's talk about them in detail.

For performance and stability, the active part of the cathode (the source of the lithium ions) is designed to have a certain atomic structure. When the ions are removed, moved to the anode, and then inserted back into the cathode, they should ideally return to the position from which they were removed in order to maintain a good stable crystal structure. The problem, however, is that the crystal structure may change with each discharge and charge. Therefore, the ions may not return to the same location. Gradually, these changes and modifications in the material change the cathode into a completely new crystal structure as well as different electrochemical properties.

As a result, the specific arrangement of atoms that initially allowed for the desired performance and stability has changed.

Corrosion problems

Degradation may also occur in other parts of the cell. Each electrode is equipped with a collector, which is a piece of metal (usually copper as the anode and aluminum as the cathode) that collects electrons and sends them to an external circuit.

If the binder stops working, the coating can strip the current collector. If the metal is corroded, then it cannot send electrons as expected. Corrosion can occur inside the cell due to the interaction between the electrodes and the electrolyte. One study showed that the graphite anode is highly susceptible to "reducing" electrons to the electrolyte, and the cathode is highly "oxidized" and can easily accept electrons from the electrolyte. As a result, it may corrode collectors made of aluminum or may form a coating on the cathode particles.

Too many decent things to do

Graphite is a common material used to make anodes. It is thermodynamically unstable in organic electrolytes. This means that the first time the cell is in charge mode, the graphite reacts with the electrolyte, resulting in a porous layer called a solid electrolyte insert or SEI.

Unfortunately, SEO is an unstable defender. There is no doubt that it protects graphite well at optimal temperatures or at room temperature. However, the SEI can partially dissolve into the electrolyte at high temperatures or when the Li-ion battery drops to zero charge.

Energy efficiency evaluation of stationary lithium-ion batteries

When it comes to battery storage systems, energy efficiency is a significant performance indicator. A comprehensive electro-thermal model of a stationary lithium-ion battery system was developed and its energy efficiency was evaluated.

The model provides a holistic approach to measuring conversion losses and auxiliary power consumption. Sub-models for the power electronics, thermal management, battery rack, and control and monitoring components were also developed and integrated into a comprehensive model. The simulation relied on the parameterization of a 192 kWh prototype system using a lithium iron phosphate battery connected to a "low voltage" grid.

Key loss mechanisms were identified, thoroughly examined and modeled. In addition, generic profiles with multiple system operation modes were estimated to characterize the fixed battery system. Typically, the losses in the "power electronics" are greater than the battery losses under low power operating systems. Conversion round-trip efficiencies were measured in the range of 70% to 80%. The overall system efficiency for photovoltaic cell applications is reduced by 8% to 13%.

This is entirely dependent on the efficiency of the lithium-ion battery. Just remember that the battery life depends heavily on how you maintain it.