lithium battery gas overproduction is a critical bottleneck restricting the performance, safety, service life, and industrial application of lithium batteries in the global R&D, production, and application chain. Among various lithium plating cases, the one caused by excessive gas production during storage or cycling is the most common. This failure not only leads to rapid capacity decay and sharp internal resistance increase of batteries but also greatly raises the safety risks of battery bulging and thermal runaway, becoming a major technical challenge that the industry urgently needs to solve.
Disassembling such faulty batteries reveals that the electrode surface is generally uneven. In severe cases, long strip-shaped purple spots are scattered around the creases of the electrode sheets, and uneven lithium deposition occurs at the edges or centers of the purple spots. The core cause of this phenomenon is that the gas production rate inside the battery far exceeds the gas discharge rate. The excess gas accumulates in the gaps of the electrode sheets and is difficult to discharge, continuously scouring the electrode sheets and damaging their surface flatness, which directly or indirectly lengthens the migration path of lithium ions. Areas with abnormal paths form purple spots or black spots due to insufficient lithium intercalation, while the edges of abnormal areas induce lithium plating due to drastic changes in electrochemical conditions. More alarmingly, this process is not a single failure but forms a closed-loop chain deterioration reaction of gas production → interface damage & electrochemical condition deterioration → lithium plating → more gas production, which continuously degrades battery performance and safety. This article will break down the four key stages of this chain reaction layer by layer to clearly present the formation logic of purple spots and lithium plating.
lithium battery gas overproduction: The Fundamental Trigger of the Chain Reaction
During the normal cycling process of lithium batteries, the natural formation of the solid electrolyte interphase (SEI) and cathode electrolyte interphase (CEI), as well as the occurrence of a small number of side reactions, will produce a small amount of gas. This is a normal phenomenon of electrochemical reactions and will not cause substantial impact on battery performance. However, the abnormal situation of lithium battery gas overproduction is often caused by various non-ideal working conditions or material problems, which is the starting point of the entire chain failure. The main incentives are divided into three categories:
First, violent electrolyte decomposition. Overcharging, high-temperature working environment, or excessively high battery operating voltage will promote violent redox reactions of the electrolyte on the surfaces of the positive and negative electrodes, leading to rapid decomposition of the electrolyte and release of a large amount of gas. Relevant research on electrolyte stability can be referred to in the latest publication of the Journal of Power Sources, which systematically elaborates on the decomposition mechanism of different types of electrolytes under extreme conditions.
Second, side reactions caused by impurities. If there are impurities such as moisture and hydrogen fluoride (HF) inside the battery, they will undergo a series of chemical reactions with the electrolyte and lithium salts, generating a large amount of gases such as hydrogen (H₂), carbon dioxide (CO₂), and ethylene (C₂H₄). For detailed standards on impurity control in battery production, you can visit the official website of the International Electrotechnical Commission (IEC) for relevant guidelines and technical specifications.
Third, repeated damage and repair of the SEI film. During the cycling process of lithium batteries, the negative electrode will expand and contract in volume, which will cause the formed SEI film to rupture. The battery will regenerate the SEI film on the newly exposed lithium surface of the negative electrode. This repair process will continuously consume lithium sources and electrolytes, and be accompanied by the production of a large amount of gas. For in-depth research on SEI film stability, you can refer to the research results published on ScienceDirect, which focuses on the modification methods of SEI films to improve their cycle performance.
Gas Accumulation: Inducing Dual Physical and Chemical Damage to Electrode Interfaces
When the gas generated by lithium battery gas overproduction cannot be discharged in a timely manner, it will continue to accumulate inside the battery, especially at the electrode interface. This stage is a key transition link from “abnormal gas production” to “lithium plating”, which directly causes physical isolation and chemical environment imbalance inside the battery, laying a core hidden danger for purple spots and lithium plating.
On one hand, interface contact failure forms electrode “dry areas”. The accumulated bubbles will occupy the effective reaction sites on the surface of the electrode active material, directly blocking the close contact between the electrolyte and the electrode material, and forming “dry areas” without electrolyte wetting on the electrode surface. In this area, lithium ions cannot normally complete the intercalation/deintercalation electrochemical reaction, and the local current density drops directly to zero.
On the other hand, uneven electrolyte wetting hinders ion transmission. The generation, movement, and accumulation of bubbles will completely break the uniform distribution of the electrolyte inside the battery, leading to a significant deterioration of the electrolyte wetting effect in local areas of the electrode. The migration of lithium ions has to bypass the areas covered by bubbles, which directly causes a significant decrease in the local ionic conductivity inside the battery, a sharp increase in ion transmission impedance, and the complete disruption of the normal migration path of lithium ions. For more research on electrolyte wetting in batteries, you can refer to the technical reports released by the Electrochemical Society (ECS).
Drastic Changes in Electrochemical Conditions: The Final Trigger of Purple Spots and Lithium Plating
The dual physical and chemical damage of the electrode interface will directly lead to drastic and irreversible changes in the internal electrochemical environment of the battery. This stage becomes the final trigger for the formation of purple spots and lithium plating, and the originally stable electrochemical reaction balance is completely broken, resulting in severe abnormalities in the intercalation and deintercalation behavior of lithium ions.
Firstly, the current density is redistributed to form a local concentration effect. The originally uniformly distributed current inside the battery will be forced to concentrate on the electrode areas that still maintain good contact with the electrolyte due to the formation of “dry areas”. The local current density in these areas will increase several times, forming an obvious current concentration effect.
Secondly, the overpotential increases sharply, triggering the thermodynamic conditions for lithium plating. The sharp increase in ion transmission impedance makes the migration of lithium ions from the electrolyte to the surface of the negative electrode extremely difficult. To maintain the total current of the battery unchanged, the local potential of the negative electrode must become more negative to “pull” the lithium ions to complete the migration. When the local potential of the negative electrode is pulled below 0V (vs. Li⁺/Li), the thermodynamic conditions for lithium plating are officially formed. At this time, lithium ions no longer intercalate into the graphite layer normally, but directly gain electrons and precipitate on the surface of the negative electrode in the form of metallic lithium, that is, lithium plating occurs. In areas with abnormal lithium ion migration paths, purple spots or black spots are formed due to insufficient lithium intercalation, which coexist with lithium plating. Relevant research on the thermodynamic mechanism of lithium plating can be found in the papers published on Nature Energy, which provides a detailed theoretical basis for the judgment of lithium plating conditions.
Lithium Plating Aggravation: Forming an Irreversible Vicious Cycle of Performance Degradation
The occurrence of lithium plating is not the end of such failures, but rather becomes a core incentive for a new round of lithium battery gas overproduction, allowing battery failures to enter a self-reinforcing irreversible vicious cycle. This is also the fundamental reason why such batteries experience performance collapse, bulging, and even thermal runaway.
The precipitated metallic lithium, especially the dendritic lithium plating product, has a super large specific surface area, which will undergo violent side reactions with the electrolyte inside the battery, generating a thicker, looser, and less stable SEI film. This process not only continuously consumes valuable lithium sources and electrolytes, further reducing battery capacity, but also releases more gas. The newly added gas will further aggravate the contact failure of the electrode interface and the blockage of ion transmission, inducing more serious lithium plating behavior.
This cycle of “gas production → interface damage → lithium plating → more gas production” will continue to self-reinforce, directly causing a sharp drop in battery capacity, a drastic increase in internal pressure (battery bulging), and a continuous rise in internal resistance. At the same time, the risk of thermal runaway of the battery increases exponentially, eventually leading to the complete loss of battery performance and safety. For technical solutions to prevent battery thermal runaway, you can refer to the guidelines released by the International Battery Safety Association (IBSA), which provides practical suggestions for battery safety design and operation.
Core Conclusions
lithium battery gas overproduction during storage and cycling is not a simple local process or material failure, but a key precursor and core driving factor that breaks the balance of electrochemical reactions and structural stability inside the battery, and induces purple spots and lithium plating.
In-depth and systematic understanding of the complete mechanism of purple spots/lithium plating caused by lithium battery gas overproduction, as well as the logic of the closed-loop chain deterioration reaction behind it, is of crucial theoretical value and engineering practical significance for the safe structural design of lithium batteries, electrolyte formula optimization, SEI film modification, quality control in the production process, as well as state diagnosis, health assessment, and full-life cycle prediction during battery use. At the same time, the analysis of this mechanism also provides a clear direction for the industry to develop targeted solutions, such as optimizing battery sealing and gas discharge structures, improving the high-temperature stability of electrolytes, enhancing the mechanical strength and cycle resistance of SEI films, and strictly controlling the impurity content in the battery production process, which provides core theoretical support for the development of lithium batteries towards higher safety and longer service life.
For more in-depth research on lithium battery performance and failure mechanisms, you can visit our internal technical page on battery material research, which collects the latest research results and technical insights from global experts. In addition, the official website of the Battery Research Institute also provides a large number of open-access technical resources for researchers and manufacturers to reference and exchange.