Why Li-ion Batteries Lose Their Capacity | Dr Melanie Loveridge |

Dr Melanie Loveridge is Associate Professor of Electrochemical Materials at WMG, University of Warwick.
In this free-to-attend SCItalk on 6 August 2020, she discussed the reasons behind capacity fade in lithium ion batteries, outlining just how complex the degradation can be.
How do we understand root causes of failure and avoid safety incidents with lithium ion batteries? Why do we analyse batteries while they are charging and discharging - so-called operando characterisation? Such approaches are critical to advancing and evolving the advanced manufacturing of new battery materials.
Visit www.soci.org/events to discover more SCItalks and a rage of other fascinating talks on myriad topics relating to science and innovation in industry.

[@flashsushi1843]

Wonderful explanation and illustration.
Can't wait for solid state batteries where the remaining issues are just dendrite formation in the anode and expansion/contraction of the electrodes.

[@douwemonsma5874]

Very nice comparison with Troy and graphical illustrations of the loss mechanisms, but a list of loss contributors seems to be missing at the end, so here they are:
Lithium-ion batteries can lose capacity over repeated charge-discharge cycles due to a number of different mechanisms. These effects occur throughout the battery, from the anode to the cathode, as well as in the electrolyte and at the interfaces between these components (high charge or discharge current can accelerate these loss mechanisms). Here are some of these mechanisms, starting from the anode:
1. Solid-Electrolyte Interphase (SEI) Formation (Anode): The SEI is a layer that forms on the surface of the anode (typically made of graphite or other carbon material in most commercial Li-ion batteries) due to reaction with the electrolyte during the initial charging cycles. The SEI can protect the anode from further reactions, but its formation consumes lithium ions and thus reduces the battery's initial capacity. In addition, if the SEI is not stable (e.g., it continues to grow or it cracks and reforms), it can lead to further capacity loss over time.
2. Lithium Plating (Anode): If the battery is charged too quickly, lithium ions may not have time to intercalate into the anode and instead may deposit on the anode's surface, forming metallic lithium. This process, known as lithium plating, is irreversible and can result in a permanent loss of capacity. It can also lead to the formation of dendritic structures, which can cause internal short circuits and pose safety risks.
.3 Electrolyte Decomposition: The electrolyte (which sits between the anode and the cathode) can decompose over time due to reactions with the anode and the cathode, particularly at high voltages and temperatures. This decomposition can consume lithium ions, leading to capacity loss, and can also contribute to the growth of the SEI and the cathode-electrolyte interface (CEI).
4. Loss of Active Material (Anode and Cathode): Mechanical stress from the volume changes that occur during lithium intercalation and deintercalation can cause particles of the anode and cathode to crack or fracture, leading to a loss of electrical contact and thus a loss of capacity. The binders and conductive additives used in the electrode can also degrade over time, leading to a loss of electrical contact.
5. Cathode Material Degradation: The cathode material can undergo a range of chemical and physical changes that reduce its capacity over time. These include the dissolution of transition metals, phase changes in the cathode material, and the loss of lithium ions due to side reactions. The exact mechanisms depend on the specific cathode material (e.g., lithium cobalt oxide, lithium iron phosphate, lithium nickel manganese cobalt oxide, etc.).
6. Cathode Electrolyte Interface (CEI) Formation: Similar to the SEI on the anode, a passivation layer can also form on the cathode surface due to reactions with the electrolyte. The formation and continuous growth of the CEI layer can lead to an increase in internal resistance and a decrease in capacity.
7. Gas Generation: Both the anode and cathode can react with the electrolyte to produce gases, such as carbon dioxide (CO2), oxygen (O2), and hydrogen (H2). These gases can build up and cause the battery to swell, which can damage the internal structure and lead to a loss of capacity.
8. Cathode Electrolyte Loss: In some cases, the electrolyte can react with the cathode material and get consumed, particularly under high-voltage conditions. This leads to a decrease in the amount of liquid electrolyte available for ion transport, increasing the internal resistance and decreasing the battery's capacity.
9. Impurity Effects: Impurities in the anode, cathode, or electrolyte materials can catalyze unwanted reactions or interfere with the normal operation of the battery, leading to capacity loss.
10. Thermal Runaway: Under certain conditions (such as overcharge, short circuit, or extreme heat), batteries can undergo a process called thermal runaway, where internal reactions rapidly increase the battery's temperature. This can lead to the breakdown of the anode, cathode, and electrolyte materials, resulting in a significant loss of capacity.
11. Loss of Electrolyte to the Anode (Lithium Dendrite Formation): When lithium metal forms on the anode as a dendrite, it can react with the electrolyte to form SEI. This consumes the electrolyte, reducing the number of available lithium ions.
12. Interface Impedance Growth: Over time, the impedance at the anode and cathode interfaces can grow, possibly due to continued SEI and CEI growth. This increased resistance can lower the effective capacity of the battery by making it harder for ions to move from one electrode to the other.
13. Structural Disorder in the Anode or Cathode Materials: Cycling can induce changes in the crystal structure of the anode or cathode materials. These changes can disrupt the pathways for lithium-ion transport, making the battery less efficient and reducing its capacity.

[@davidmcnamara8024]

Your big brain has caused dendrite formations in my small brain capacity. The amount of useful knowledge tumbling toward me is overwhelming. The work done is of critical importance and endlessly fascinating. Staggering in its complexity. Author, Author!

[@kbobek23]

This was a masterpiece of intersectional nerdiness!

[@swiftrian]

At 14:20. Carbon is obviously the best conductor. So creating "diamond's" has been a thing for awhile. As we inch closer to mores law, what can we expect?

[@deeeeeeps]

The clouds have been making lightning for millions of years and still work great. Don't fight moisture and oxygen ..use it!