Why is The Square LFP Battery Aluminum Shell Positively Charged?
By HY-MeganJune 30th, 2025391 views
In the field of lithium-ion batteries, prismatic battery has become the mainstream choice of solar energy energy storage and electric vehicles due to its stable structure, high group efficiency and controllable cost. However, one key design is often misunderstood: why does the aluminium case need to be connected to the cathode? This is not simply "electrified", but a sophisticated strategy by the lithium iron phosphate battery manufacturer to balance safety and longevity. 1. Five scientific mechanisms of positive charge in aluminum shells
(1) Lithium-aluminum alloy: Because the octahedral void size of the lattice of metallic aluminum is similar to that of Li, it is easy to form metallic interstitial compounds with Li, if all the octahedron in the metallic aluminum lattice are embedded in Li, an alloy with the chemical formula LiAl will be formed. With the further occurrence of the corrosion reaction, lithium element, lithium oxide, lithium hydroxide and lithium intercalated aluminum compounds react with carbon dioxide in the air to form Li2Co3 and a small amount of [Al2Li(OH)6]2CO3, at this time, the battery will gradually fail. (2) Aluminum and graphite potential: The lithium intercalation potential (VS Li /Li) of aluminum is about 0.3V, which is higher than the lithium intercalation potential of graphite anode (0.01-0.2V). If both aluminum and graphite are anode materials, then metallic aluminum will have a preferential lithium intercalation reaction over graphite. Therefore, in order to avoid corrosion of the aluminum metal shell, it is necessary to keep the potential of the aluminum shell above its lithium intercalation potential. (3) Electrochemical corrosion: The standard electrode potential of aluminum is -1.66 V (relative to the standard hydrogen electrode), while copper is 0.337 V, which is prone to oxidation reaction (Al→Al³⁺ 3e⁻) in the electrolyte (such as organic solvents containing LiPF₆), resulting in the dissolution of aluminum metal and the formation of corrosion pits. (4) High potential of the positive electrode: When the lithium-ion battery is charged, the positive electrode is at a high potential (usually 3V to 4.5V or even higher than that of lithium metal). At this potential, many metals are corroded by oxidation. At this high potential, aluminum quickly forms a very dense, insulating alumina passivation film. This film prevents further oxidation and corrosion of the aluminum, allowing the aluminium to work stably at this potential for a long time. (5) Protection: If the shell is not charged, there is a potential difference between the internal positive electrode and the shell, which may cause microcurrent through electrolyte or internal short circuit, which will affect the battery life for a long time. Moreover, when the housing is grounded or connected to the positive electrode, the monitoring and protection circuitry in the battery management system can be simplified.
2. Technical challenges and manufacturing-end solutions
Although the aluminium shell is positively charged to protect against corrosion, it can exacerbate the risk of thermal runaway – high potentials can easily cause arcing in the event of a puncture or short circuit. To this end, the leading lithium iron phosphate battery manufacturer adopts two types of innovative solutions: (1) Active disconnect mechanism: connect the positive electrode and the aluminum shell through the normally closed relay to cooperate with the voltage/temperature/pressure sensor. When abnormal, the circuit is cut off to make the aluminum shell turn into a neutral structure. (2) Insulation barrier: add a ceramic-coated separator, PET insulating film, or full-coverage tab tape to the outer layer of the cell to avoid contact between the negative electrode and the shell.
3. The unique advantages of LFP prismatic batteries in solar energy storage
With its anti-corrosion design of aluminum shell, Lifepo4 prismatic battery has achieved two major breakthroughs in the field of solar energy: (1) Ultra-long cycle life: Lithium iron phosphate (LFP) material is naturally resistant to high temperature, combined with the potential control of aluminum shell, the number of cycles is > 2000 times, far exceeding that of ternary batteries (about 1500 times). (2) Safety and economy: The lightweight aluminum shell (the density is only 1/3 of the steel shell) reduces the weight of the system, while the anti-corrosion design reduces the maintenance cost. For example, in solar energy, the LCOE of Lifepo4 prismatic battery is 30% lower than that of ternary batteries.
The aluminium design of the square Lifepo4 prismatic battery is essentially the ultimate control of materials chemistry and engineering by lithium iron phosphate battery manufacturer. As solar energy's demand for energy storage surges, leading players are driving two innovations: (1) Intelligent potential monitoring: AI algorithm is used to control the shell voltage in real time to predict the corrosion risk; (2) Solid-state electrolyte integration: Fundamentally eliminate the erosion of the aluminum shell by the electrolyte, and improve the reliability of the Lifepo4 prismatic battery in extreme environments. In the future, with the optimization of the manufacturing process, Lifepo4 prismatic battery will continue to dominate the high-safety and long-life solar energy storage scenario, and the aluminum shell anti-corrosion technology will also become the core battlefield of lithium battery innovation.
