Types of lithium batteries
Currently, the main types of rechargeable batteries used in the market are nickel-metal hydride (Ni-MH) and lithium-ion (Li-ion). Among lithium-ion batteries, two types are already in mass production: liquid lithium-ion batteries (LiB) and polymer lithium-ion batteries (LiP). Therefore, in many cases, a battery labeled "Li-ion" is definitely a lithium-ion battery. However, it is not necessarily a liquid lithium-ion battery; it could also be a polymer lithium-ion battery.
Lithium-ion batteries are an improved version of lithium batteries. Lithium batteries have existed for a long time, but lithium is a highly reactive metal (remember its position on the periodic table?), making it unsafe to use. It often caught fire or exploded during charging. Later, improved lithium-ion batteries were developed, incorporating components that suppress the reactivity of lithium (such as cobalt and manganese), thus making lithium batteries truly safe, efficient, and convenient. The older lithium batteries were subsequently largely phased out. To distinguish between them, you can look at the battery markings: lithium batteries are marked with "Li," while lithium-ion batteries are marked with "Li-ion." Currently, the so-called "lithium batteries" used in laptops and mobile phones are actually lithium-ion batteries.
The basic structure of a modern battery includes three elements: a positive electrode, a negative electrode, and an electrolyte. As a type of battery, lithium-ion batteries also possess these three elements. Generally, lithium-ion technology uses liquid or inorganic colloidal electrolytes, thus requiring a robust casing to contain the flammable active ingredients. This increases the battery's weight and cost, and also limits the flexibility in size and design. Generally, the minimum thickness for liquid lithium-ion rechargeable batteries is 6mm; reducing it further becomes quite difficult.
Polymer lithium-ion batteries are those that use polymer materials as their primary battery system in at least one of the three main structural components. The new generation of polymer lithium-ion batteries has achieved a high degree of polymerization, allowing for thinner profiles (as thin as 0.5 mm), arbitrary area, and arbitrary shape, greatly improving the flexibility of battery design. This allows for the creation of batteries of any shape and capacity to meet product requirements. Furthermore, polymer lithium-ion batteries offer 50% higher energy density than current conventional lithium-ion batteries, and their capacity, charge/discharge characteristics, safety, operating temperature range, cycle life, and environmental performance are all significantly improved compared to conventional lithium-ion batteries.
Currently available liquid lithium-ion (LiB) batteries are prone to overcharging, which can cause the safety valve to rupture and catch fire, posing a significant danger. Therefore, it is essential to install a protection IC circuit to prevent overcharging. In contrast, polymer lithium-ion batteries exhibit better charge/discharge tolerance compared to liquid lithium-ion batteries, thus allowing for more relaxed requirements on the external protection IC circuitry. Furthermore, polymer lithium-ion batteries can utilize constant current charging via an IC, significantly reducing charging time compared to the CCCV (Constant Currency-Constant Voltage) charging method used in lithium-ion rechargeable batteries.
Application of lithium batteries by mobile phone manufacturers
Although almost all manufacturers have tended to use lithium-ion batteries in recent years, major mobile phone manufacturers around the world still have their own characteristics and habits in battery selection. For example, during the same historical period:
Nokia: Uses Ni-MH (nickel-metal hydride) batteries and LiB (liquid lithium-ion) batteries, but not LiP (polymer lithium-ion) batteries.
Ericsson: Uses Ni-MH batteries, LiB batteries, and LiP batteries.
Motorola: Uses Ni-MH batteries and LiB batteries, but not LiP batteries.
It's easy to see that Ericsson demonstrated its pioneering spirit in mobile phone technology by being among the first to choose LiP polymer lithium-ion batteries for its phones. According to my research, the main manufacturers of polymer lithium-ion batteries are currently Japanese companies such as Sony, Panasonic, and GS, with a production volume of 21 million units in 2000, 50% of which were supplied to Ericsson mobile phones. By 2002, lithium-ion batteries were widely used and adopted in mobile phones from other manufacturers. However, the use of polymer lithium-ion batteries was far from being ubiquitous in all mobile phone manufacturers' products; widespread adoption still has some time to go.
On the other hand, while lithium-ion batteries have many advantages, they also have drawbacks, such as high price and limited charge/discharge cycles. Lithium-ion batteries can only withstand 400-600 charge/discharge cycles, with even specially modified products reaching just over 800. In contrast, nickel-metal hydride (NiMH) batteries can withstand over 700 charge/discharge cycles, with some high-quality products reaching 1200. Therefore, NiMH batteries have a longer lifespan than lithium-ion batteries. Furthermore, NiMH batteries are significantly cheaper than lithium-ion batteries. Strictly speaking, lithium-ion batteries also exhibit a memory effect, but it is extremely low and practically negligible.
Therefore, it is clear that there is no perfect battery at present.
Proper use of lithium-ion batteries
This is the focus of this article, and we will discuss it in three points.
1. How to charge a new battery
It's important to note that lithium batteries enter a dormant state after being stored for a period of time, at which point their capacity is lower than normal, and their usage time is shortened. However, lithium batteries are easily activated; just 3-5 normal charge-discharge cycles are sufficient to activate them and restore their normal capacity. Due to the inherent characteristics of lithium batteries, they have virtually no memory effect. Therefore, new lithium batteries in a user's mobile phone do not require special methods or equipment for activation. Not only is this true in theory, but in practice, using standard charging methods from the beginning—this "natural activation" method—is the best approach.
Regarding the "activation" of lithium batteries, many people believe that charging time must exceed 12 hours, repeated three times, to activate the battery. This claim of "charging for more than 12 hours for the first three times" is clearly a continuation of the practice with nickel batteries (such as nickel-cadmium and nickel-metal hydride). Therefore, this claim is fundamentally a misconception. Lithium batteries and nickel batteries have very different charging and discharging characteristics, and I can assure you that all the serious, official technical documents I have consulted emphasize that overcharging and over-discharging can cause significant damage to lithium batteries, especially liquid lithium-ion batteries. Therefore, it is best to charge according to the standard time and method, and especially avoid charging for more than 12 hours. Generally, the charging method described in the phone's instruction manual is the standard charging method suitable for that phone.
Furthermore, lithium-ion battery phones and chargers automatically stop charging once the battery is fully charged; there is no "trickle" charging for 10+ hours as claimed by nickel-cadmium chargers. In other words, leaving your lithium-ion battery on the charger after it's fully charged is pointless. And since no one can guarantee that the battery's charge/discharge protection circuitry will never change or that its quality will be flawless, your battery will be constantly teetering on the edge of danger. This is another reason why we oppose prolonged charging.
Furthermore, on some mobile phones, if the charger is not removed after a certain charging time, the system will not only not stop charging, but will also begin a discharge-charge cycle. While manufacturers may have their reasons for this practice, it is clearly detrimental to the lifespan of the battery and the phone/charger. Additionally, long charging times often require overnight charging, and given the state of my country's power grid, voltage levels are often higher and fluctuate significantly at night. As mentioned earlier, lithium batteries are very delicate and far less tolerant of charging and discharging fluctuations than nickel-cadmium batteries, thus introducing additional risks.
Furthermore, another aspect that cannot be ignored is that lithium batteries are also not suitable for over-discharge, as over-discharge is also very detrimental to lithium batteries. This leads to the following question.
2. When should charging begin during normal use?
We often see the argument that because the number of charge-discharge cycles is limited, phone batteries should be completely drained before recharging. However, I found an experimental table regarding lithium-ion battery charge-discharge cycles, and the data on cycle life is listed below:
Cycle life (10% DOD): >1000 cycles
Cycle life (100% DOD): >200 cycles
DOD stands for Depth of Discharge. As the table shows, the number of rechargeable cycles is related to the depth of discharge; the cycle life at 10% DOD is much longer than at 100% DOD. However, if we consider the relative total capacity of actual charging: 10% * 1000 = 100, 100% * 200 = 200, the latter's complete charge-discharge is still better. But the previous comment needs some correction: Under normal circumstances, you should recharge according to the principle of using up the remaining battery power before recharging. However, if you anticipate that your battery won't last the entire day the next day, you should start charging it promptly. Of course, if you're willing to carry a charger to the office, that's another matter.
When you need to charge your battery in preparation for an important event that is expected to cause heavy communication, even if the battery still has plenty of charge left, you can charge it in advance. This is because you are not actually losing "1" charge cycle life, which is only "0.x" times, and often this x will be very small.
The principle of fully discharging the battery before recharging doesn't mean going to extremes. A widely circulated saying, similar to prolonged charging, is "try to completely drain the phone's battery, ideally until it shuts down automatically." This practice actually originated with nickel-cadmium batteries to avoid the memory effect, but unfortunately, it's still prevalent with lithium-ion batteries. There have been cases where people continued using their phones after receiving low battery warnings, continuing until they automatically shut down. In these cases, the phones became unresponsive to charging and powering on, requiring repair. This was because the battery voltage was too low due to over-discharge, rendering it incapable of charging and powering on properly.
3. The correct way to handle lithium battery mobile phones
In summary, my most important advice regarding charging and discharging lithium battery mobile phones is:
① Charge according to the standard time and procedure, even for the first three times;
② When your phone displays a low battery warning, you should start charging it as soon as possible;
③ Lithium batteries do not require special activation methods; they will activate naturally during normal phone use. Insisting on using the widely circulated method of "activating with three 12-hour long charges" will actually be ineffective.
Therefore, all practices that pursue 12-hour ultra-long charging times or use lithium battery phones until they automatically shut down are wrong. If you have been following these incorrect practices, please correct them as soon as possible; it may not be too late.
Of course, if the phone and charger have good protection and control circuitry, the lithium battery is well protected. Therefore, understanding the charging rules is key, and in some cases, compromises can be made. For example, if you find your phone must be charged before you go to sleep, you can start charging it before bed. The crucial point is that you should know the correct procedure and not deliberately follow incorrect instructions.
