Archive for the ‘Auto’ Category

Recently, the topic of spontaneous combustion of lithium-ion batteries often flashes in the news headlines: the smartphone lights up, the hover board, or the car. So what happens inside the battery during thermal acceleration and why does spontaneous combustion occur?

Elements of Lithium-ion batteries:

Lithium-ion batteries consist of an anode and a cathode, separated by a porous polymer separator. The cathode active material is most often transition metal oxides with lithium ions embedded in the crystal. Graphite is commonly used in the anode. The electrolyte, which is filled with an electrochemical cell, is an organic solution of lithium salts. When the manufacturer first charges, when lithium is embedded in the anode on the electrodes (especially on the anode), a protective ion-conducting layer (SEI) is formed, consisting of decomposed electrolyte. This layer protects the electrodes from parasitic reactions with electrolyte.

Causes of explosion:

The most common cause of spontaneous combustion of batteries is a short circuit inside the electrochemical cell. Electrical contact between the anode and the cathode can occur for many reasons. This may be, for example, mechanical damage to the cell. Another internal short circuit arises due to the violation of production technology in case of uneven cutting of electrodes or metal particles between the anode and cathode, which leads to damage to the porous separator. Also, the cause of the internal short circuit may be the “germination” of metal lithium chains (dendrites) through the separator. This effect occurs if lithium ions do not have time to integrate into the anode crystal when charging too fast or at low temperatures, as well as if the capacity of the cathode active material exceeds the capacity of the anode. Right now MapQuest explores the different aspects of the complications that arises.

Since reactions with electrolyte are exothermic, the temperature and pressure inside the battery continue to rise. When the temperature reaches 180–200 ° C, the cathode material, usually a transition metal oxide with lithium embedded in the crystal, reacts to disproportionate and liberates oxygen. This is where the spontaneous combustion and even more sharp temperature jumps occur. In parallel, there is a thermal decomposition of the electrolyte (200-300 ° C), which also produces heat. It looks like this:

Fully loaded:

The batteries are also equipped with fuses and valves, which, when the pressure and temperature inside increase, either disconnect the electrodes from the circuit, or contribute to the release of accumulated gas. In the latter case, since the gases are flammable, a flame arises when it comes into contact with oxygen outside. An example of the action of safety valves could be observed in an accident involving the Tesla car Model S, where the battery was punctured by a large metal object. Since in Tesla the battery valves were aimed down on the asphalt and the individual blocks were well isolated from each other, only the front of the battery burned (as Elon Musk said, if the same metal object broke through the gasoline tank, the car would burn completely).

Twenty years ago there was not such a big choice of bicycles. Most people skated on a reliable bike, used when driving on any roads. Of course, it is easier to move on dirt roads on a mountain bike for this purpose. And on a lighter road, you can move faster on an asphalt road.

With the advent of the sale of many imported copies and their specialization, many people do not know how to choose a bicycle, considering:

Take a moment and accurately measure your height without shoes. Its actual growth is important to know in order to choose the right Sports bike with regard to its growth. There are times when people call it with an error as much as 10 cm.

This is the size of the frames of bicycles in inches, centimeters or written in conventional notation. Large frames (L, XL, XXL) are assembled from thicker pipes to support the greater weight of the taller cyclist. The smaller bike has an average weight of 150-200 grams smaller than the neighboring, larger, growth. A bicycle with a small frame is more maneuverable and easier to hold in a vertical position than a car with a huge frame. On models with a large frame, you can take the ideal position to develop the maximum speed.

Grid Mesh manufacturer

First of all, when choosing a bicycle, you need to look at the size grid of a particular firm. Such tables should be made by the manufacturer of bicycles. Often the necessary information can be found when searching in online stores. If the manufacturer did not provide such information, then you can choose a bicycle on the universal grid.

Universal mesh

Especially precisely the standard grids allow you to pick up a bicycle with a classic frame, assembled from two triangles.

Indirect definition

There is also a computational method for determining the growth, which will be useful for buying through the online store. To properly place a bike order, you will need to measure your height from groin to floor and multiply the resulting measurement in centimeters by a factor of 0.66 for a road bike, or 0.57 for a mountain bike. The result of the calculation is a flyover in centimeters. To translate the result into inches, it is enough to divide the value by 2.54.

Test drive

If you can ride a bike that you like, be sure to try a new car. When buying in the market or in a store, set the bike between your legs, touching the back of the saddle spout. In this position between your groin and the frame should be free space of at least 10 cm, that is, approximately at the width of the palm. Riding a bike with a too high frame is dangerous, because in case of danger, you jump off without hesitation, from the saddle and hit the crotch on the upper tube of the frame.