Li / SOCl2 batteries have many excellent properties:

(1) The highest voltage among all batteries, the open circuit voltage of the single battery reaches 3.6 ~ 3.7V;

(2) The voltage is stable and the load voltage accuracy is high. When the discharge current speed is 1mA / cm, the voltage is 3.3V, and the voltage remains unchanged within the energy range of the battery above 90;

(3) The specific energy in the primary battery is high, SOCl2 is both a solvent and a positive electrode active material, and the theoretical energy is as high as 1875Wh / kg and 2013Wh / kg. The actual specific energy is as high as 600Wh / kg, the medium rate discharge is 400Wh / kg, and the low rate discharge is 300Wh / kg.

(4) Wide operating temperature range, from -55 ℃ ～ + 85 ℃, excellent performance at high temperature and low temperature

(5) Long battery storage life. The self-discharge rate is less than 1%. Because lithium forms a LiCl protective film on the electrolyte surface. Make lithium very stable in electrolyte, plus battery sealing structure. The shelf life of the battery is up to 10 years.

Although Li / SOCl2 battery is commercialized later than other lithium batteries, it is a rising star. Has become the main lithium battery series produced in the world today. There are many types and types of Li / SOCl2 batteries today: there are dozens of button-type, cylindrical and rectangular batteries. The capacity ranges from several mA · h to hundreds of thousands of mA · h, which is mainly used for cardiac pacemakers and CMOS support power. At the same time, it also has a lot of applications in the military field, mainly used for artillery shells, missiles, fuzes and water needs. At present, low and medium rate batteries are widely used.

However, the current Li / SOCl2 battery has a problem of failure after storage, which affects the reliability of the battery. Reliability refers to the ability of a product to perform a specified function under specified conditions and within a specified time, and is one of the important indicators of product quality. For Li / SoCl2 batteries, the significance of introducing the concept of reliability is to enable the product to have a very high quality guarantee during storage and use. and so. In recent years, more and more attention has been paid to the reliability management of battery production. There are many factors that affect the reliability of Li / SOCl2 batteries, such as insufficient initial charge to cause early battery failure, poor sealing performance caused by electrolyte leakage, battery self-discharge, voltage lag, etc.

1 Research on sealing performance

It is generally believed that sealing is the basic condition for ensuring the storage life of batteries. Under good sealing conditions, it can not only prevent the leakage of electrolyte, but also prevent the infiltration of external water vapor and oxygen. Because SOCl2 is a highly corrosive liquid, the casing of Li / SOCl2 battery is made of stainless steel with good corrosion resistance, the pole is also wrapped with stainless steel, and the battery uses a hermetically sealed structure. Even so, the electrolyte often leaks, causing the failure of Li / SOCl2 batteries stored at room temperature and causing significant corrosion outside the batteries.

The accelerating method of battery heating was used to accelerate the test of the sealing performance of small Li / SOCl2 batteries. Observe the tightness with a scanning electron microscope. As a result, it was found that the weld seam of the stainless steel remained good, and its weakness was the uneven performance of the joint between the ceramic and the stainless steel and the sealing ceramic. The combined effect of temperature, stress and corrosion causes the ceramic sealing insulator to rupture, the sealing performance is lost, and the electrolyte leaks.

The key to improvement lies in the development of suitable sealing materials and the improvement of the connection process between sealing materials and stainless steel.

2 Initial capacity study

The three small Li / SOCl2 batteries with slightly different structures and manufacturing processes were observed at high temperature and compared with the results at normal temperature. The discharge experiment results were analyzed with reference to ISo 2859, and the expiration date of the battery was discussed. It was pointed out that the lack of initial charge is one of the main causes of early failure of the battery, because for a well-sealed battery, the reduction in battery capacity is mainly due to the internal self-discharge of the battery The reaction consumes active materials, so the reliability of small Li / SoCl2 batteries is closely related to their internal capacity.

3 Voltage lag study

3.1 Adding additives

3.1.1 Add PVC (polyvinyl chloride), VC-VOC (polyethylene-vinylidene chloride copolymer)

In 1.5mol / L LiAlCl4-SOCl2, the neutral electrolyte (with and without PVC additives)