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why do lithium batteries swell

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why do lithium batteries swell

Lithium-ion batteries are widely promoted for their high lifespan and capacity. However, with prolonged use, some lithium-ion batteries may experience swelling due to the following reasons:

  1. Expansion Caused by Overcharging Overcharging leads to all lithium atoms in the positive electrode material moving to the negative electrode material. This results in deformation and collapse of the originally full grids in the positive electrode, a significant factor contributing to the decrease in battery capacity. During this process, an increasing amount of lithium ions accumulates in the negative electrode, leading to the overaccumulation of lithium atoms that grow into tree stump-like crystals, causing the battery to swell.

  2. Expansion Caused by Overdischarging The Solid Electrolyte Interface (SEI) film serves a protective function for the negative electrode material, preventing the material structure from collapsing and extending the cycle life of the electrode material. The SEI film undergoes reversible changes during charge and discharge, with some organic compounds experiencing reversible transformations. Excessive discharging of the battery leads to reversible destruction of the SEI film, and after the SEI protecting the negative electrode material is damaged, the negative electrode material collapses, resulting in the expansion of lithium-ion batteries.

  3. Issues in Production and Manufacturing Processes Due to the diversity of manufacturers, some may prioritize cost-cutting measures, leading to adverse production environments and the use of outdated equipment. This can result in uneven coating of the battery, and the introduction of dust particles into the electrolyte. These factors may contribute to the swelling of lithium-ion batteries during user use, potentially posing greater risks.

why are lithium batteries better

Lithium batteries have become widely favored for various reasons since the development of the first battery, the voltaic pile. Over time, there have been improvements leading to the popular use of disposable carbon-zinc batteries, rechargeable nickel-metal hydride (NiMH), nickel-cadmium (NiCd), and lead-acid batteries. In 1992, Sony successfully introduced the lithium-ion battery, and its advantages have significantly impacted many aspects of modern life.

  1. Higher Energy Density: Lithium batteries have a higher energy density, approximately 2.5 times that of nickel-cadmium batteries and around 6-7 times that of lead-acid batteries. This means that lithium batteries can provide the same capacity in a smaller and lighter package.

  2. High Operating Voltage: Lithium batteries have a higher rated voltage compared to batteries like nickel-cadmium or nickel-metal hydride, making them more versatile in various applications.

  3. Environmentally Friendly and Non-Polluting: Lithium batteries do not contain harmful metals such as cadmium, lead, or mercury, making them environmentally friendly and less polluting.

  4. Long Cycle Life: Lithium batteries can endure a high number of charge and discharge cycles, with cycle counts ranging from 800 to 2000. This significantly surpasses lead-acid batteries (approximately 300 cycles) and nickel-metal hydride batteries (around 500 cycles), resulting in a longer overall lifespan.

  5. Low Self-Discharge Rate: Lithium-ion batteries exhibit a very low self-discharge rate. The self-discharge rate measures the spontaneous loss of stored charge when the battery is in an open circuit state. Lithium-ion batteries, such as lithium iron phosphate batteries, typically have a self-discharge rate of around 2% per month at room temperature, which is much lower than the 25% self-discharge rate of nickel-metal hydride batteries.

  6. Strong Adaptability to Temperature Extremes: Lithium batteries can operate in a wide temperature range, from -20°C to 60°C. Some lithium batteries are designed for specific environments with varying temperature requirements, and certain types can even function in environments with temperatures exceeding 100 degrees Celsius.

 
 
 

why do lithium batteries last longer？

We generally use cycle counts to indicate the lifespan of lithium-ion batteries. While the cycle counts vary among different lithium-ion batteries, overall, their cycle life can typically reach around 5-6 years, and with proper usage, it can extend even further. This is significantly longer compared to the lifespan of lead-acid batteries, which is around 1.5 years. Lithium-ion batteries can endure a high number of charge and discharge cycles, with cycle counts ranging from 800 to 2000 cycles. In comparison, lead-acid batteries have approximately 300 cycles, and nickel-metal hydride batteries have around 500 cycles. This higher cycle count contributes to the longer overall lifespan of lithium-ion batteries.

what lithium batteries are not allowed on airplanes ？

Regarding this issue, it is necessary to distinguish between lithium batteries that are restricted for carriage and those that are prohibited for carriage.

  1. Restricted Carriage of Lithium Batteries: With airline approval, electronic devices containing lithium batteries with a capacity exceeding 100Wh but not exceeding 160Wh are allowed to be carried on board. Each passenger can carry up to two such spare batteries, and they must not be checked in. Devices that may contain lithium batteries exceeding 100Wh include media equipment, audiovisual production equipment, performance props, medical devices, electric toys, power tools, toolboxes, etc.

  2. Prohibited Carriage of Lithium Batteries: Large lithium batteries or electronic devices with a capacity exceeding 160Wh are strictly prohibited from being carried or checked in.

To determine whether the lithium batteries you are carrying can be taken on board, you can generally check the markings on the batteries. If the rated energy in watt-hours (Wh) is not directly labeled on the lithium battery, you can calculate it using the following methods:

  • If the nominal voltage (V) and nominal capacity (Ah) are known: Calculate the rated watt-hours using the formula: Wh = V x Ah. Nominal voltage and nominal capacity are usually marked on the battery.

  • If the battery is marked only with milliampere-hours (mAh): Divide the marked value by 1000 to obtain ampere-hours (Ah). For example, if a lithium battery is marked with a nominal voltage of 3.7V and a nominal capacity of 760mAh, the rated watt-hours would be: 760mAh / 1000 = 0.76Ah; 3.7V x 0.76Ah = 2.9Wh.

when do lithium batteries catch fire？

The fundamental cause of lithium-ion battery ignition is the abnormal retention of heat within the battery, leading to ignition after reaching the ignition point of internal and external combustibles. The specific reasons for this occurrence include:

  1. Internal Short Circuit: Abuse of the battery, such as overcharging and overdischarging leading to dendrite formation, impurities or dust during battery production, can deteriorate and pierce the separator, causing micro short circuits. The release of electrical energy results in temperature rise, and the material’s chemical reactions due to the temperature increase further expand the short-circuit path, creating a larger short-circuit current. This cumulative and mutually reinforcing destruction leads to thermal runaway. Internal short circuits in lithium-ion batteries can cause a large current to flow through the short circuit point, generating a significant amount of heat, thereby triggering explosions or fires.

  2. External Short Circuit: Extended external short circuits generally burn weak points in the circuit and rarely lead to thermal runaway events in the battery.

  3. External High Temperature: Due to the characteristics of lithium-ion battery structure, various reactions generate a considerable amount of heat. Melting of the separator causes internal short circuits, and the release of electrical energy increases the production of heat. This cumulative and mutually reinforcing destructive effect results in the ejection of electrolyte and combustion. If lithium-ion batteries are exposed to high temperatures for an extended period, the solvent in the electrolyte evaporates faster, the electrode material expands, internal resistance increases, and battery capacity gradually decreases. When the temperature reaches a certain level, it may cause leakage, short circuits, leading to explosions or fires.

  4. Mechanical Vibration or Damage: If lithium-ion batteries experience strong mechanical vibration or damage during transportation, use, or maintenance, it may damage the battery’s separator or electrolyte, causing direct contact between metallic lithium and electrolyte. This contact triggers an exothermic reaction, ultimately leading to explosions or fires.

There are various reasons for the explosion and ignition of lithium-ion batteries. It is crucial to use and maintain batteries safely, exercise effective battery management, and be vigilant about identifying battery manufacturers to prevent the use of substandard products.

 
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