Why is The Square LFP Battery Aluminum Shell Positively Charged? Revealing The Core Technology of Anti-corrosion and Energy Storage Applications.

In the field of lithium-ion batteries, the square Lifepo4 prismatic battery has become the mainstream choice for solar energy storage and electric vehicles due to its advantages such as stable structure, high group efficiency and controllable cost. However, a key design is often misunderstood: Why does the aluminum shell need to be connected to the positive electrode? This is not a simple "charge", but a sophisticated strategy of the lithium iron phosphate battery manufacturer to balance safety and life.

(1) Lithium aluminum alloy: Since the size of the octahedral voids in the aluminum lattice is similar to that of Li+, it is very easy to form a metal interstitial compound with Li+. If all the octahedrons in the aluminum lattice are embedded with Li+, an alloy with the chemical formula LiAl is formed. As the lithium is embedded deeper, it gradually reacts to form lithium oxide and lithium hydroxide, so the corrosion sample is alkaline after dissolution. As the corrosion reaction continues, lithium, lithium oxide, lithium hydroxide, and aluminum compounds embedded with lithium 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 insertion potential of aluminum (VS Li+/Li) is about 0.3V, which is higher than the lithium insertion potential of graphite negative electrode (0.01-0.2V). If aluminum and graphite are both negative electrode materials, aluminum will undergo lithium insertion reaction before 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 insertion potential.
(3) Electrochemical corrosion: The standard electrode potential of aluminum is -1.66V (relative to the standard hydrogen electrode), while copper is 0.337 V. It is easy to undergo oxidation reaction (Al→Al³⁺+3e⁻) in electrolyte (such as organic solvent containing LiPF₆), causing aluminum metal to dissolve and form corrosion pits.
(4) High positive electrode potential: When lithium-ion batteries are charged, the positive electrode is at a high potential (relative to lithium metal, usually 3V to 4.5V or even higher). At this potential, many metals will be oxidized and corroded. Aluminum will quickly form a very dense, insulating aluminum oxide passivation film at this high potential. This film prevents further oxidation and corrosion of aluminum, allowing aluminum to work stably for a long time at this potential.
(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 the electrolyte or internal short circuit, affecting the battery life in the long term. Moreover, after the shell is grounded or connected to the positive electrode, the monitoring and protection circuits in the battery management system can be simplified.

Although the positive charge of the aluminum shell can prevent corrosion, it may increase the risk of thermal runaway - when punctured or short-circuited, the high potential can easily cause an arc. To this end, the head lithium iron phosphate battery manufacturer adopts two types of innovative solutions:
​​(1) Active disconnection mechanism: Connect the positive electrode and the aluminum shell through a normally closed relay, and cooperate with voltage/temperature/pressure sensors. In the event of an abnormality, the circuit is cut off and the aluminum shell is converted to a neutral structure.
​​(2) Insulation barrier: Add a ceramic coating diaphragm, PET insulation film, or fully cover the ear tape on the outer layer of the battery cell to prevent the negative electrode from contacting the shell.

Lifepo4 prismatic battery has achieved two major breakthroughs in the field of solar energy by virtue of its anti-corrosion aluminum shell design:
(1) Ultra-long cycle life: Lithium iron phosphate (LFP) material is naturally resistant to high temperatures, and combined with aluminum shell potential control, the number of cycles is >2000 times, far exceeding ternary batteries (about 1500 times).
​(2) Safety and economy: The lightweight aluminum shell (density is only 1/3 of that of steel shell) reduces system weight, while the anti-corrosion design reduces maintenance costs. For example, in solar energy storage power stations, the cost per kilowatt-hour of Lifepo4 prismatic battery is 30% lower than that of ternary batteries.

The square Lifepo4 prismatic battery's aluminum shell design is essentially the lithium iron phosphate battery manufacturer's ultimate control of material chemistry and engineering. With the surge in demand for solar energy storage, leading manufacturers are promoting two innovations:
(1) Intelligent potential monitoring: Using AI algorithms to control the shell voltage in real time and predict corrosion risks;
(2) Solid electrolyte integration: fundamentally eliminate the corrosion of the electrolyte on the aluminum shell and improve the reliability of the Lifepo4 prismatic battery in extreme environments.

In the future, with the optimization of manufacturing processes, the Lifepo4 prismatic battery will continue to dominate the high-safety and long-life solar energy storage scenarios, and aluminum shell anti-corrosion technology will also become the core battlefield of lithium battery innovation.