Can 12V lithium iron phosphate batteries replace lead acid batteries?

Invention of the lead-acid battery

In the southern half of the far side of the moon, there is a large meteorite impact crater formed about 3.9 billion years ago, which was named "Plant Crater" in 1970, also called "Plant Crater".

     The crater is named after the French physicist Raymond-Louis Gaston Planté (1834-1889), the inventor of the lead-acid battery who made outstanding contributions to the modern automobile industry .

Gaston Plante was born in the Pyrenees-Atlantic province, which is the land in the lower left corner of the modern French territory. It belongs to the Aquitaine region. In history, it was classified as Eleanor of Aquitaine. British territory, and then returned to France.

      Gaston Prandtl is a genius, studying at the Sorbonne for his undergraduate degree, earning a Bachelor of Arts at 16, a Bachelor of Science at 19, a Master of Science at 21, and at the 26-year-old École Nationale des Beaux-Arts Professor of Physics.

Is it amazing to be a physics professor at 26? No, because Gaston Prandtl invented the lead-acid battery at the age of 25, and the commercial rechargeable battery he invented was on top of the car invented by Mr. Karl Benz in the future. promotion on a global scale.

It is normal for feats higher than the sky to be engraved on the moon.

Promotion of lead-acid batteries

The lead-acid battery is "a" secondary battery, and also the "first" secondary battery, because the secondary battery before the lead-acid formula has not been officially mass-produced, and the lead-acid formula has been approved by French chemist Camille Al After the improvement of Camille Alphonse Faure (1840 – 1898), mass production was realized, and the mass production enterprises came from Luxembourg engineer, inventor and entrepreneur Henri Owen Tudor (1859-1928), Mr. Tudor (this surname can also be translated as "Tudor") improved lead-acid battery actually took 5 years and 2 months to be scrapped, which solved the problem of the short life of the secondary battery.

The first thing after the lead-acid battery is mass-produced is to provide temporary lighting power for the train body that stops at the train platform. At the same time, a considerable part is used to manufacture electric vehicles. The picture shows a pure electric car powered by Tudor lead-acid batteries. .

Before the mass production of secondary batteries, all electric vehicles are only experimental products, because the primary batteries they use are scrapped when they are used up. The arrival of the lead-acid battery announced the birth of the power battery, because it can really drive a car for dozens of kilometers, and it is an alternative power for cattle and horses.

       The early internal combustion engine vehicle products did not have an electrical system. The cranking handle was used to start (that is, the "key" of the walking tractor today), the horn was solved by a bell, and the headlights were directly powered by the internal combustion engine.

In 1918, the predecessor of AMC, the Hudson Motor Car Company, brought 6V voltage into the assembly sequence of mass production vehicles, and gradually gave birth to the assembly of on-board lights and on-board starters, and the use of lead-acid batteries. Production began to increase. After entering the 1950s, the large American V8 engine with a displacement of 6-8L often made the waist and legs of the 6V voltage system sore. The budget engineer connected two 6V lead-acid batteries in series, and it became a 12V lead-acid battery, which has been used to this day.

Of course, 12V is not the only voltage for lead-acid batteries. The diesel engines of some heavy-duty vehicles are very large and heavy. You can connect two 12V batteries in series to become 24V batteries, or three series to become 36V.

The principle of lead-acid battery

Why are lead-acid batteries only used to drive golf carts and not powertrains for passenger cars?

It's not impossible. The Nissan Tama (1947) in the picture below is driven by lead-acid batteries, but the top speed is only 34km/h and the battery life is 65km. The photoelectric battery was removed and fully charged.

The reason is that the energy density of lead-acid batteries is very low. Even after a century and a half, the current lead-acid batteries can only achieve about 35-40Wh/kg (about 80-90Wh/L), which is too heavy and has too little power. .

Take our commonly used 12V lead-acid battery as an example, the capacity is only 0.6-1.2kWh (generally more than 1kWh is used for medium and large vehicles of luxury brands), and the output power is only 5kW (of course, there is a cold start power of more than 10kW). The gasoline engine is enough, and you can listen to music in the car for more than half an hour, but the air conditioner can only last for dozens of seconds before the compressor stops, because this is not a deep cycle battery.

The industrial chain of lead-acid batteries is extremely mature and the structure is very simple. In a fully charged state, the negative plate of a lead-acid battery is lead, the positive plate is lead dioxide, and the electrolyte solution has a relatively high concentration of aqueous sulfuric acid, which stores most of the chemical energy.

If it is overcharged, part of the water will be electrolyzed into oxygen and hydrogen. At this time, it must be refilled with pure water to replenish the electrolyte.

   When discharging, the positive and negative plates will become lead sulfate (II) (PbSO4), the electrolyte loses sulfuric acid to obtain water, and the electric energy is released.

       The lead-acid battery is full of liquid, has high density, heavy weight, and urgent energy density, but its stability is particularly good, the number of cycles is large, the global industrial chain is mature, and the cost is relatively low, so it is used in many industries. for example:

1. Starter battery: Used in the starter part of the car, it is lighter than the deep cycle battery of the same size, and has a longer service life, generally lasting 3-5 years.

2. Power battery: Two-wheeled and three-wheeled electric vehicles are preferred. The new national standard stipulates that four-wheeled electric vehicles should use lithium batteries, in addition to golf carts, electric forklifts, etc. The power battery must be a deep cycle battery, and the energy storage potential must be tapped.

3. Energy storage battery: The energy storage battery used in RVs and ships is designed to have a larger capacity than the starting battery, but it is not as deep as the deep cycle battery charge and discharge, and the life / energy storage is in between.

4. Backup power supply: uninterruptible power supply UPS, communication base stations, and alarms also use lead-acid batteries as energy storage, which are gradually replaced by lithium-ion batteries. This kind of battery is very important to the number of cycles, and the longer the life, the better.

The battle between EFB and AGM technology schools

In the past, there were only tape players and radios in the car, and even so, you often had to bring a "cross the river" to prevent the weak car battery from falling off the chain. After entering the 21st century, the electrical equipment on new cars (including audio-visual entertainment systems, active safety systems, seat heating massage, etc.) has increased dramatically, and the engine self-start-stop system has gradually become a standard item for mainstream passenger cars. Synchronous upgrades can adapt to this era.

Of course, 12V lead-acid batteries have changed a bit since the 1990s. In the past, the on-board battery only needed to start the warm-up without doing much work. Now the 12V battery needs to constantly work to cope with the self-starting and stopping conditions in the urban congestion environment. Timely shutting down the engine, such as when queuing in front of a red light, or shutting down a vehicle with a taxiing function before reaching the red light, can improve the thermal efficiency of the heat engine to a certain extent, save fuel and reduce emissions.

In Germany alone, greenhouse gas emissions have already been reduced by 40% in 2020. Carbon emissions targets have had a huge impact on the auto industry, which is considered a major source of pollution, even if the auto industry does not share the accusation. For the general public, emission-free electric vehicles are still a little far away (not the main sales volume for the time being), and now the most feasible energy-saving and emission-reduction solution is the engine self-start-stop technology, which corresponds to the new 12V lead-acid battery - EFB Battery (Enhanced Flooded Battery) and AGM battery (Absorbent Glass Mat Battery).

The "Enhanced" of EFB means that the battery is optimized for the charging limit and cycle life, so as to cope with the high frequency and high current charging and discharging that comes with frequent self-starting and stopping, because each self-starting and stopping action of the engine will correspond to a certain amount of electricity. High current surge.

     When the engine is off, all the on-board electrical systems just mentioned are powered by the 12V lead-acid battery alone. If you install an old set of lead acid batteries from the 90s, it will twitch to death because neither the power nor the capacity is up to the electrical demands of modern models. This kind of old battery is not impossible to install, but is waiting to be scrapped by the on-board electrical system after it is installed. Its aging speed is beyond your imagination, so the current passenger car must be equipped with an EFB battery as a minimum.

       When you buy medium and large vehicles, luxury brand models, performance models, etc., you will find an AGM battery placed in the cabin. AGM stands for "Absorbent Glass Mat" and uses a glass mat Separator that absorbs acidic solvents and prevents leaks.

The second difference between AGM and EFB is the compaction of the lead plates. Because the AGM lead plate is more tightly compacted, the battery is more shock-resistant and also helps to promote electrochemical reactions, so the cycle life of AGM battery is higher than that of EFB, and it can be charged and discharged normally for a longer time.

       EFB and AGM are the products of two different processes for starting wet batteries, and the principle is the same. When fully charged, the open circuit voltage is generally around 12.8V, and if it drops below 12.4V, it will automatically charge.

We just mentioned that the SLI series batteries do not support self-start and stop, so the charging curve of the SLI on the left side of the figure below is "starting energy consumption - charging - gentle", while the self-start-stop battery (EFB and AGM) on the right side of the figure below The charging curve is in a constant cycle" Start consumes energy - charge - smooth - kinetic energy back

      Compared to EFB batteries, AGMs are chemically more active and can withstand higher frequency self-start-stop and high inrush currents from kinetic energy recovery systems.

Can I change the AGM for a car with EFB as standard?

The answer is: it can be used temporarily, but it will age faster.

Let's take a look at the differences between EFB and AGM lead-acid batteries:

1. AGM is currently the strongest civilian 12V battery technology, and the price is about 1.5 times that of EFB batteries.

2. The theoretical life of AGM is 4-6 years, and the theoretical life of EFB is 3-5 years. If the lead-acid battery is designed in the rear compartment (front engine solution), because there is no engine to bake at high temperature day and night, the life will be longer.

3. AGM has no acid leakage, stronger cold start function and stronger high current surge tolerance.

It can be seen that EFB and AGM are basically the same in function, but there are differences in performance. There is no doubt that EFB is more cost-effective, but models with standard AGM cannot be backward compatible with EFB for a long time, while models with standard EFB can be upward. Compatible with AMG.

    In addition, if you are like me, the first thing last time is to wear seat belts, the second thing is to start the ignition, and the third thing must be to turn off the automatic start-stop system, then you can use the waste EFB/AGM to start and stop automatically. Replacing lead acid batteries with lower cost SLI batteries?

Answer: No, because the power demand (load) of the on-board electrical system of modern automobile products is very high, even if the automatic start-stop system is not used, the demand for instantaneous high current will be reduced, and other on-board electrical systems will consume a lot of power. Acid batteries can't support this task.

Some FAQs

A. How long does a 12V battery usually run out of power?

This indicator tests the self-discharge rate of the lead-acid battery, that is, the charge retention ability.

In theory, the self-discharge rate of lead-acid batteries is between 20-30%, that is, between 20-30% in a month, but in practice it is far more than this ratio.

Under normal circumstances, a 12V lead-acid battery in a healthy state can barely start after standing for 30 days, and it will hang after more than 30 days. If a car can't catch fire after only 15 days or even 10 days of standing still, it's better to replace the 12V lead-acid battery quickly.

       B. What are the signs that lead-acid batteries are rushing to the streets?

1. The engine ignition is weak, and it is even lit a few times.

2. Press the horn without starting the engine, the sound is weak.

3. Some instruments have battery warning lights, and some display battery voltage.

      4. When going for maintenance, some dealers and factory workers will help you measure the voltage with an electric meter, and then write it in the report.

5. After the cycle life is used up, the battery is exhausted. At this time, we will say the battery life EOL (End Of Life). In some cases, the battery is dead during driving, that is, when driving, the high temperature inside the cabin has become the last straw that crushes the camel when the battery cannot be charged. At this time, the instrument panel and headlights will meet. Light and dark.

C. Do 48V mild hybrid vehicles still need 12V lead-acid batteries?

1. Yes, all current 48V light-hybrid vehicles require 12V lead-acid batteries.

2. The 48V battery generally uses a lithium-ion battery pack to serve high-load components such as engine self-start and stop, air conditioning, electronic anti-roll bars, and air suspension.

      3. 12V lead-acid batteries are used to power low-load components such as door locks, anti-theft devices, and audio.

4. The 12V lead-acid battery of the 48V light-hybrid vehicle is still a consumable product and needs to be replaced after several years of use.

D. Do new energy vehicles still need 12V lead-acid batteries?

1. Yes, even pure electric vehicles also need 12V lead-acid batteries.

2. When the 12V lead-acid battery is insufficient, the high-voltage power battery of the new energy vehicle will charge it, but according to the logic set by different manufacturers, some new energy vehicles may not be able to open the door lock because the 12V battery is dead. , we have encountered this.

3. Low-load electrical assemblies such as car anti-theft systems and door locks do not need to use 200V-400V high-voltage power batteries at all. Therefore, when the new energy vehicle is stopped, the high-voltage power will be "powered off" to save power. loss, only 12V is used for vehicle monitoring.

4. Like 48V light hybrid vehicles, 12V lead-acid batteries of new energy vehicles are still consumables.

E. Does the ancient lead-acid battery have a future?

1. Previously, some Saihua vehicles used 12V lithium batteries to replace heavy lead-acid batteries, and now some civilian vehicles have begun to use lithium batteries instead. For example, BYD DM-i hybrid uses self-produced 12V lithium iron phosphate batteries, and the weight is only 2.2 ± 0.2kg.

     2. The industrial chain of traditional 12V lead-acid batteries is very complete and cost-effective. Even if they are gradually retired on vehicles, they can continue to be used on non-mobile platforms, and their industrial scale is in decline.

3. The task of reducing the weight of lead-acid batteries is extremely difficult to achieve. The skills of this technology tree have been fully filled. The next thing to do is to replace lead-acid with lithium-ion batteries.

4. The advantage of the lead-acid formula is that the thermal runaway is very low, and very few vehicles spontaneously ignite due to the thermal runaway of the lead-acid battery. In addition, the working temperature of lead-acid batteries is as wide as -20 ℃ -60 ℃, which is unmatched by most current lithium batteries.