How to extend the life of electric vehicle lead-acid batteries?

First, the headache of electric vehicle battery problems For electric bicycles, the development momentum is extremely rapid. The actual annual output in recent years has surpassed the social reserves. This is an astonishing figure, which indicates that the production and sales of electric vehicles are experiencing the most glorious history. In this booming market, making money is not too difficult. However, every advantaged industry has “soft ribs.” If you want to ask bosses who fight in this industry, what is the most headache for the distribution of electric cars, the only answer is the short battery life.

Now most manufacturers have promised battery warranty for one year. Of course, the business is so publicized, but the problem came out after six months, a large number of users come back, they are not to the second consumer, nor to introduce friends to buy a car, but to replace the battery . Even if battery manufacturers fulfill their warranty commitments, users will not be satisfied. They will think that this is a quality issue for electric vehicles. Dealers spend a lot of energy and cannot avoid complaints. Perhaps this problem lies with the battery manufacturers, but battery manufacturers also have difficulties. Battery design and cyclical discharge tests have shown that the battery cycle life is indeed one and a half years or even two years, and the quality of the battery is strictly controlled during production. After six months, many batteries will age. Some manufacturers have begun to try to replace lead batteries with longer-lived solid batteries, nickel batteries, and even lithium batteries. However, the high cost has lost the competitive advantage in the market for the above-mentioned class-dominated consumer groups. Many manufacturers have the spirit of pioneering and enterprising. Relentlessly defeated. We all know that the lifespan of many electronic products such as televisions and computers can be as long as 10 years, but manufacturers only provide a one-year warranty, while electric vehicle batteries last up to two years of life, and battery manufacturers must insist on One year warranty, this is to conceal the unhelpful reality of the battery life of electric vehicles, and at the same time to stabilize consumer confidence. This "bare-faced" warranty method can also withstand a short period of time, a long time, the problem will always emerge. Therefore, there are many guerrilla-type manufacturers in this industry. They take a half-year cycle, do not establish a fixed customer base, and seek their personal interests at the expense of the interests of the entire industry.

How to improve the battery life, how to improve the use of the battery environment and other issues are all very disappointing but concerned about the issue. In order to clarify the way to prolong the battery life, we must first clarify the failure mechanism of the battery in order to remedy the disease.

Second, the reasons for the short service life of electric vehicles lead-acid battery from 1859, the French Gaston Prentt discovered the phenomenon of lead-acid charge and discharge, lead-acid batteries have been the most widely used products in the field of batteries, such as cars, motorcycles, ships There are lead-acid batteries on aircraft, back-up equipment, and backup power supply equipment, but we have also heard many complaints from these fields about lead-acid batteries. However, why the same products are on electric bicycles is actually a "fear of complaints." Below we explain the reasons for this problem from several aspects.

1. Reasons for working principle of lead-acid battery The charging and discharging process of lead-acid battery is the process of electrochemical reaction. When charged, lead sulfate forms lead oxide, and lead oxide is reduced to lead sulfate during discharge. Lead sulfate is a substance that is very easy to crystallize. When the lead concentration in the electrolytic solution of the battery is too high or the static lead time is too long, it will “pinch” into small crystals that attract the surrounding crystals. The lead sulphate, like a snowball, forms a large inert crystal. After being charged, the crystallized lead sulphate can not only be reduced to lead oxide, but also precipitated on the electrode plate, resulting in a decrease in the working area of ​​the electrode plate. This phenomenon is called Vulcanization, also known as aging. At this time, the battery capacity will gradually decline until it cannot be used. When a large amount of lead sulfate is accumulated, the lead particles are also attracted to form a lead branch, and the lead bridging between the positive and negative electrode plates causes a short circuit in the battery. If there is a gap in the surface of the plate or in the sealed plastic case, the crystal of lead sulfate will accumulate in these gaps and cause expansion tension, eventually causing the plates to break off or the housing to rupture, causing physical damage to the irreparable battery. Therefore, the main mechanism leading to the failure and damage of lead-acid batteries is the inevitable sulfidation of the battery itself.

2. The reason for the special work environment for electric bicycles is that if they are lead-acid batteries, they will cure during use, but lead-acid batteries in other fields have a longer life than lead-acid batteries used in electric bicycles. This is because electric bicycles The lead-acid battery has a work environment that is more easily vulcanized.

1 The deep discharge used in automotive lead-acid batteries is only one-way discharge during ignition, the generator will automatically charge the battery after ignition, and will not cause deep discharge of the battery. Electric bikes cannot be charged while riding, and often exceed 60% of deep discharge. When deep discharge, the concentration of lead sulfate increases, vulcanization will be quite serious.

2 The high-current discharge electric vehicle 20 km cruising current is generally 4A, this value has been higher than other areas of the battery operating current, while the overloaded electric vehicle operating current is greater. Battery manufacturers have performed cyclic life tests that are 70% charged at 1C and 60% discharged at 2C. After this kind of life test, it can reach a lot of batteries with 350 cycles of charge and discharge cycles, but the effect of actual use is very different. This is because high-current operation increases the depth of discharge by 50% and the battery accelerates vulcanization. Therefore, the battery life of the electric three-wheeled motorcycle is shorter because the body of the three-wheeled motorcycle is too heavy and the working current reaches 6A or more.

3 High frequency of charge and discharge The battery used in the backup power supply field will only be discharged when the power is cut off. If the power is stopped 8 times a year, the life of 10 years will be reached, and only 80 cycles of charge life will be used, while the electric vehicle 1 It is very common for over 300 charge and discharge cycles.

4 Short-term recharging Because the electric bicycle is a vehicle, the recharging time is not much. To complete 36-hour or 48-volt 20-hour recharging within 8 hours, it is necessary to increase the recharging voltage (typically 2.7-2.9 volts per unit). When the charging voltage exceeds the oxygen evolution voltage (2.35 volts) or the hydrogen evolution voltage (2.42 volts) of the single cell, the battery will open the valve due to excessive oxygen evolution, resulting in dehydration and increased electrolyte concentration. The vulcanization has increased.

5After discharge, it cannot be charged in time as a means of transport. The charging and discharging of electric bicycles are completely separated. It is difficult to charge them in time after discharging, and the large amount of lead sulfate formed after discharge is not recharged to lead oxide if it is more than half an hour. It will vulcanize into crystals.

3. Reasons for production of lead storage batteries Various battery manufacturers have adopted various methods for the specificity of lead-acid batteries for electric bicycles. The most typical method is as follows:

1 increase the number of plates.

The original design of the single cell 5 6-piece system was changed to 6 7-piece, 7 8-chip, or even 8 9-piece. By reducing the thickness of the plate and the separator, increase the number of plates to improve the battery capacity.

2 Increase the sulfuric acid content of the battery.

The proportion of sulfuric acid in floating batteries is generally between 1.21 and 1.28, while the sulfuric acid of batteries for electric bicycles is generally around 1.36 to 1.38, which can provide a larger current and increase the initial capacity of the battery.

3 Increase the amount and proportion of lead oxide in the positive plate active material.

Increasing the lead oxide increases the amount of electrochemical reactions involved in the discharge, increasing the discharge time and increasing the battery capacity.

Through these measures, the initial capacity of the battery satisfies the capacity requirements of the electric bicycle, and in particular, the high current discharge characteristics of the battery are improved. However, the number of plates has increased, the capacity of sulfuric acid has decreased, and the heat generated by the battery has led to a large amount of water loss. At the same time, the probability of micro-short-circuiting and bridging of the battery has increased. Increasing the specific gravity of sulfuric acid increases the initial capacity of the battery, but the vulcanization phenomenon becomes more serious. One of the most basic principles of a sealed battery is that after the oxygen is evolved from the positive plate, oxygen is directly sent to the negative plate and absorbed by the negative plate to be reduced to water. The parameter for evaluating the battery's specifications is called the “sealing reaction efficiency”. This phenomenon is called “oxygen”. cycle". In this way, the water loss of the battery is very low, and “maintenance-free” is achieved, that is, no water is added. For this reason, it is required that the capacity of the negative electrode plate be larger than that of the positive electrode plate, which is also referred to as the negative electrode transition. Increasing the active material of the positive electrode plate inevitably results in a decrease in the negative electrode transition, a deterioration of the oxygen cycle, an increase in water loss, and a vulcanization. Although these measures have increased the initial capacity of the battery, they will cause water loss and vulcanization, and water loss and vulcanization will contribute to each other. The end result is to sacrifice the life of the battery.

There is also the problem of extremely group assembly of Welds. The place where it is easy to make a weld is a plate. Each battery cell has 15 plates, that is, 15 solder joints, a battery has 6 single cells, there are 90 solder joints, a battery consists of 3 12V batteries, there are 270 solder joints . If there is a weld in a solder joint, the cell capacity will drop, and then the cell will fall behind in the cell, causing the entire cell to lag behind, and the battery will form a serious imbalance, leading to premature failure of this set of cells. Even if the imaginary welding is controlled at one ten-thousandth, on average, there will be a group of batteries that have an imaginary weld in every 37 batteries. This is absolutely not allowed. However, lead-calcium alloy grid cells will precipitate calcium during welding to hide the problem of co-welding. As a result, many battery manufacturers prefer to use low-brass alloy grids instead of lead-calcium alloys. On the other hand, the low-vanadium alloy has a lower voltage for oxygen evolution and hydrogen evolution. The battery has a large amount of gas and the water loss is relatively severe. The battery is more likely to be vulcanized.

4. Reasons for the production of electric bicycles Most vehicle controllers have left a line loss plug, and many dealers use a speed limit to attract customers. Some depots simply remove the governor from the factory, which not only attracts customers who value the speed of the car, but also reduces costs. Such vehicles have very high currents at high speeds and can severely shorten the battery life.

The minimum protection voltage of a 12V lead-acid battery is 10.5V. If it is a 36V battery pack, the minimum reserve voltage is 31.5V. At present, most controllers use a controller with an undervoltage protection voltage of 31.5V. On the surface, this is correct. However, when the battery voltage of the 36V battery pack is only 31.5V, there will certainly be a battery voltage less than 10.5V due to the battery capacity difference. The battery is in an overdischarged state. At this time, the capacity of the over-discharged battery drastically decreases. At this time, the damage to the battery is not only the single battery, but affects the life of the entire battery. In fact, after the battery voltage is lower than 32V until 27V, the added continuous line capacity is less than 2 kilometers, and the damage to the battery is very large. As long as such a situation occurs 10 times, the battery capacity will be less than 70% of the nominal capacity. In addition, some users found that after the battery was undervoltage, after 10 minutes, the battery did not undervoltage, and then to take power to drive, which is more damage to the battery, and most of the car's instructions did not give the user a warning. At present, most controllers have adjustable potentiometers inside, and the vibration drift of this adjustable potentiometer is quite serious. In the price competition, in the face of a user group that pays more attention to the appearance of the car, few products use anti-vibration precision multi-turn potentiometers, and it is not surprising that such controllers drift after vibration.

5, the reason for the charging equipment The industry is widely circulated in the sentence: the battery is not bad, it is bad enough. In order to meet the short-term high-capacity charging of an electric bicycle battery, in the three-stage constant voltage current limiting charging, the constant voltage value has to be increased to 2.47V to 2.49V. In this way, the oxygen evolution voltage of the positive plate of the battery and the hydrogen evolution voltage of the negative plate are greatly exceeded. Some charger manufacturer's products in order to reduce the indication of charging time, increase the constant voltage to float the charging current, and make the charging instructions fully charged, but not fully charged, to compensate for the increase in floating voltage. In this way, many chargers have a float voltage of more than 2.35V per cell, so that a large amount of oxygen is still being evolved during the float charging phase. The oxygen cycle of the battery is not good, so that in the floating stage is also constantly exhaust. The high constant pressure value ensures the charging time, but sacrifices water loss and vulcanization. The constant voltage value is low, and it is difficult to guarantee the charging time and charging power. In improving the battery grid alloy of the battery, increasing the gas potential, improving the oxygen cycle performance, and improving the sealing reaction efficiency, the maximum charge voltage of the control charge is 2.42 V or less, that is, below the hydrogen evolution potential. This will inevitably lead to an increase in charging time, which must be added to the negative pulse of depolarization in the state of high-current charging (current-limiting charging) to improve the battery's charge acceptance ability, and to charge more when charging at high current. Some battery power reduces the charging time. 70% of the 2C current charging is when the battery is relatively high in charge acceptance ability, the battery is charged with a large current, and the damage to the battery is relatively small. The battery is basically no higher than the severe hydrogen evolution voltage. Once above the hydrogen evolution voltage, the battery will quickly lose water. The use of such chargers, you must use continuous charge and discharge, if you stop charging a few days halfway, the battery will produce more severe vulcanization and premature failure. The use of a battery by the user cannot ensure that the battery can be charged in a timely manner after each use. If the battery is not recharged several times within one year, the vulcanization of the battery will accumulate. Most charger manufacturers say that the car manufacturer does not accept chargers that can guarantee battery life because of price factors. It should be acknowledged that this is true of most small businesses, but there are large and large companies that have developed and do not have a good charger. Some charger manufacturers exaggerate certain features and the efficacy of the finished product is not as good as it advertises. There are also many features that fall into the category of selling concepts and have limited effectiveness.

6, other reasons a lot of batteries in the monomer test, you can get better results, but for the battery string, because the capacity, open circuit voltage, state of charge, the degree of vulcanization are not the same, this difference will be Serial battery packs are enlarged, and the poor state of the monomers affects the entire battery pack, and its lifespan is significantly reduced.

Charging from the battery in the production line, to the use of the car after the user purchased the car to go through this period of time to go through many links, the interval may even be up to several months, during this period, because there is no battery to supplement the electricity, the large amount of lead sulfate generated by self-discharge Accumulation of crystals, the new battery the user has just purchased may be a battery that has been aged or even charged.

When a battery manufacturer performs a warranty, the battery recovery is not completely eliminated. After the battery returns, the battery manufacturer re-inspects the charge and discharge. In the inspection, it is often found that more than 60% of the battery cells are batteries that do not meet the return and return conditions. The reason for this is that in a series battery pack, individual batteries fall behind to form a whole group of batteries with a reduced function, causing the entire group to fall back. Many battery manufacturers re-provision, refill, and desulfurize the returned battery, and then re-provide it to the user to increase the useful life of the battery, reduce the rejection rate, and reduce part of the claims of the battery manufacturer. Therefore, many dealers have already felt that the batteries provided by manufacturers are obviously "not as good as one generation."

Third, how to solve the vulcanization of the battery To reduce the vulcanization of the battery to extend the battery life, we must first improve the working environment of the electric bicycle. Reduce the weight of the car body, remove unnecessary decorative parts, properly speed limit, do not carry heavy objects, do not need to use electric bikes for a long time to do supplementary charging, it is best to charge in time after each discharge, and do a good job of undervoltage protection. To prevent battery over-discharge, the nominal 24V undervoltage protection should be set at 21.5V to 22V. For the nominal 36V undervoltage protection, 32.5V±0.5V should be selected. For the nominal 48V, it should be set at 44V to 45V. This voltage is only less than 2 kilometers to continue to improve, but it can effectively extend the battery life. Regularly visit the professional maintenance point every three months to inspect the battery and replenish the water in time. These methods are simple and economical. However, it is difficult to strictly observe them. Therefore, special equipment can be used for sulfur removal maintenance. These methods are:

1. The use of desktop quick desulfurization equipment The principle of the desktop quick desulfurization equipment is high voltage and high current pulse charging, and elimination of vulcanization by negative resistance breakdown. This method is fast and effective, and can temporarily eliminate the effect of vulcanization. However, the high voltage and high current can also eliminate the sulfur and also remove the active material, causing serious water loss and softening of the positive plate during the elimination of vulcanization. Fatal damage to the battery, after such equipment sulfur removal twice after the battery will be basically scrapped. In addition, the current professional maintenance point for a sulfur removal charge is basically between 60 and 80 yuan, and can extend the battery life up to six months, and does not have significant economic benefits for the user. At present, professional battery maintenance shopkeepers on the market have already understood the dangers of this method. Therefore, equipment for removing sulfur by pulse discharge has appeared. In fact, the fundamental principle has not changed, but it has only changed from a constant high-voltage constant current to an instantaneous one. Peak high pressure will still damage the active material on the plate. Friends who used this type of product should be very clear about this.

2. Selectable sulfur-removable charger There are three working principles for the current sulfur-removal charger. One is similar to the working principle of the desktop quick-removing sulfur removal device. The high-voltage and large-current pulse charging is used to remove sulfur through negative resistance. It has been demonstrated that this method can be fatal to battery life and has been negated by the market. The second is the use of a fast pulse front charge and discharge pulse, which uses instantaneous peaks to interfere with battery cure during charging. The other method is to periodically use a 10% to 20% overcharge method to reduce the lead sulfate crystals of the battery. Both types of chargers can remove sulfur when charging, but it will cause under-charge or over-charge, and also ignore the fact that the battery discharge process is the most important curing process, so the effect is not ideal, most users are With a charger equipped with an electric vehicle, this reinvestment of sulfur removal method will be abandoned.

3. The use of an on-line lead-acid battery extender Inline lead-acid battery extender in parallel with a battery can prevent and eliminate vulcanization in 24 hours. This method is relatively slow to repair, repair time is relatively long, often more than 120 hours, but both charge and discharge process can prevent and eliminate the vulcanization, repair effect is very good. Because of the low voltage and low current, the extender does not have a strong impact on the battery plate, resulting in dehydration and softening. This is a kind of continuous maintenance mode that the user can devote to once, especially for new batteries with better quality. Extend the battery life by 2 to 5 times, and once invested, it can be accompanied by an electric automatic car. The next time the battery is replaced, the extender can continue to be used, which can save a lot of economic costs for the user. If the user replaces the battery once a year, a set of battery 280 yuan, the user will spend 2800 yuan on the replacement of the battery in 10 years, the conservative calculation, if you use an extension device to extend the battery life twice, 10 years can save nearly half Battery charge.

The significance of this method is very great. The first is to bring real economic benefits to the user, reducing the user's trouble. The second is to increase the reputation of the depot and provide conditions for expanding production. Thirdly, it is difficult for electric vehicle dealers to solve the problem of battery warranty, reduce complaints, increase credibility, and increase profits. At the same time, it also increases the sales plan that facilitates transactions in store sales. Fourth, the battery manufacturer’s claim fees can be greatly reduced. Fifth, improve the image of electric bicycles and expand the overall development of electric bicycles. Sixth, improving the utilization of batteries is conducive to environmental protection.