Lithium batteries are distinguished from other chemical batteries by their high energy density and low cycle cost. However, “lithium battery” is an abstract and vague term. There are six common chemical components of lithium batteries, each of which has its own unique advantages and disadvantages. The main chemical component of renewable energy applications is lithium iron phosphate (LiFePO4). LiFePO4 has many advantages, such as high safety performance, high thermal stability, high rated current value, long cycle life, abuse resistance and so on.
Compared to almost all other lithium chemicals, lithium iron phosphate (LiFePO4) is very stable. The battery is assembled from a cathode material (iron phosphate) that is naturally safe. Iron phosphate has many advantages over other lithium chemicals, such as promoting strong molecular bonds, enduring extreme charging conditions, extending cycle life, and maintaining chemical integrity throughout many cycles. As a result, these cells are characterized by strong thermal stability, long cycle life and resistance to abuse. LiFePO4 batteries are hard to overheat and do not suffer from “thermal runaway” conditions, so they cannot overheat or catch fire in the event of total misoperation or adverse environmental conditions.
Lithium batteries differ from immersion lead acid and other batteries in their chemical composition. They don’t emit dangerous gases like hydrogen and oxygen, and they don’t run the risk of coming into contact with corrosive electrolytes like sulfuric acid and potassium hydroxide. In general, these batteries can be stored in sealed areas, so there is no risk of explosion, and better systems such as well-designed ones do not require active ventilation or cooling.
Lithium-ion battery modules, like lead-acid batteries and many other types of batteries, are made up of many cells, but the difference is that lead-acid batteries have a nominal voltage of 2V/cell, whereas lithium batteries have a nominal voltage of 3.2V. Therefore, if you want to achieve a 12V battery, generally need to connect four batteries in series. This gives the LiFePO4 a nominal voltage of 12.8V. A 24V battery with eight cells in series has a nominal voltage of 25.6V; Sixteen cells connected in series into a 48V battery have a nominal voltage of 51.2V, and 12V, 24V, and 48V inverters work well at these voltages.
Lithium batteries are often used as a direct replacement for lead-acid batteries because their charging voltage is very similar to that of lead-acid batteries. The maximum voltage of the four-cell LiFePO4 battery (12.8V) is generally in the 14.4-14.6V range (depending on manufacturer recommendations). Lithium-ion batteries have many unique features. They do not absorb charge and do not need to maintain a constant voltage state for long periods of time. In general, the case where the battery does not need to be charged is when the battery reaches its maximum charging voltage. LiFePO4 batteries also have a unique discharge characteristic. When discharging, a lithium battery remains at a higher voltage under load than a lead-acid battery. With lithium-ion batteries, it is common to go from a full charge to a discharge of 75 percent, but only a fraction of a Ford, so it is not easy to know how much capacity has been used without a battery detection device.
One significant advantage of lithium batteries over lead-acid batteries is that they do not suffer from defect cycles. Essentially, the battery can’t be fully charged until it discharges again the next day. For lead-acid batteries, this becomes a big problem. If the defect is repeated over and over again, the plate degrades severely. LiFePO4 batteries do not need to be recharged regularly. In fact, one way to improve overall life is to partially charge rather than completely.
Efficiency is an important factor in designing solar power systems. The average lead-acid battery has a round-trip combined efficiency (from full to no and back to full charge) of about 80%. Other chemical reactions could be worse. The round-trip energy efficiency of lithium iron phosphate batteries is as high as 95-98%. This is a major improvement for a system that is starved of solar power in winter, and the fuel savings from charging the generators are huge. The rapid absorption charge phase of lead-acid batteries is very inefficient, resulting in operating efficiencies of 50 percent or less. Considering the amount of charge a lithium-ion battery does not absorb, it can take as little as two hours to charge the battery from full discharge to full charge. It should be noted that lithium-ion batteries can also have an almost complete discharge rating with no significant adverse effects. But the most important thing is to make sure that the stable individual cells don’t overcharge at all. This is the work of the integrated Battery Management System (BMS).
There is a big problem, and the big problem is the safety and reliability of lithium-ion batteries, so all the components have an integrated battery management system (BMS) to face this problem. BMS system is used to monitor, evaluate, balance, and protect cells from “safe operating area” accidental operation system, at the same time, the BMS system is a basic security component in lithium ion battery systems, it is used to protect and detect internal battery, the battery can prevent excessive current, voltage too high or too low, too high or too low temperature damage to the battery. LiFePO4 batteries are permanently damaged when their voltage drops below 2.5V or rises above 4.2V. The BMS system plays a big role in monitoring each battery and preventing battery damage if the voltage is too low or too high.
The BMS system also has another basic responsibility. This basic responsibility is for the BMS to balance the battery pack during the charging process and ensure that all the batteries are fully charged but not overcharged. LiFePO4 battery cells do not actively balance after charging. Because the impedance across the cells varies slightly, no cell is exactly the same. So in this cycle, some of the batteries will be charged early, or discharged early. When cells are unbalanced, the variance between cells also increases significantly over time.
In a lead-acid battery, the current will continue to flow when one or more cells are fully charged because of the internal electrolysis of the cell, which is divided into hydrogen and oxygen. This current helps the other batteries fully charge, so naturally, it balances out all the battery charges. However, in a fully charged lithium battery, there is a lot of resistance and a small flow current. So, lagging batteries can’t be fully charged. During the balancing process, to prevent the battery from being overcharged, the BMS adds a small load to the fully charged battery and allows other batteries to catch up.
Lithium-ion batteries have many advantages over other chemical batteries. They are a relatively safe battery solution because there is no fear of thermal runaway or catastrophic meltdown, and this is an important possibility for other types of lithium-ion batteries. These batteries have a very long cycle life, with some manufacturers even guaranteeing 10,000 cycles. These batteries are gaining increasing attention within the industry due to their high C/2 continuous discharge and charging efficiency, and up to 98% round-trip efficiency. LiFePO4 is also a perfect solution for energy storage.