Tesla Electric Cars. Does it have the best battery in the business? index

1.Tesla Electric Cars. Does it have the best battery in the business?

Tesla Electric Vehicles are fantastic to drive and low cost to run.

Tesla - some of the best new technology !

Batteries are one of the most important technologies used by any electric vehicle, and Tesla already has some of the best. Tesla is soon going to update us on its latest battery technologies, and this analysis will provide the information that you need to understand those updates.

The timing of the battery day announcements is highly likely to be dependent on the completion and publication of a whole string of new battery related patent applications presently going through the patent process. When the patents are granted and published we will have our battery day!

So what makes a good battery?

Why are Tesla's batteries so good?

and how can Tesla improve them further?

Will the model Y use any of these improvements?

There are many different factors that contribute to a good battery, and most of these factors interact with each other, so the big question is - what is the optimum balance of these factors for the best battery?

What do we need from a good battery? - an Overview

A battery is not a simple structure like a fuel tank!

We want to store the most energy in the smallest mass: 

We want to store the most energy in the smallest volume:

When we store energy, we want to get almost all of it back again.

When we store energy, we don't want it leaking away over time:

We want to be able to charge as fast as possible without damaging the battery. For many battery designs this means having the battery at the right temperature. Warming it up if it is too cold and cooling it down if it is too hot. Then as soon as charging has finished changing the battery temperature to the optimum temperature for driving the EV, or the optimum temperature for when the EV is not in use.

So ideally we want a battery that is stable and usable over a very wide temperature range. But with existing chemistries we need battery packs with efficient heating and cooling systems to keep the battery at the optimum temperature, and a very good battery management system (BMS) 

We want to be able to charge as efficiently as possible - when we buy more electricity we want to be able to store of much of it as possible, and when the vehicle is regenerating electricity by slowing itself down we want to store as much of that recovered energy in the battery.

We want to be able to use as much of the battery capacity as possible without damage to the battery - to charge to as near full as we can and then discharge to as near empty as we can.

We want to be able to go through the charge and then use cycle as many times as possible, without the battery losing the ability to store and supply energy.

We don't want batteries catching fire, or releasing dangerous chemicals in an accident, or have runaway reactions if something goes wrong.

We want the process of manufacture to be as easy, low cost, and as safe as possible, not use any dangerous chemicals or produce dangerous waste products, and as non polluting as possible.

We want the batteries and their components to be fully recyclable when they are no longer needed in an electric vehicle - as efficiently and cheaply as possible.

We want the raw materials for battery construction to be readily available and low cost.

We want the process of battery pack assembly to be as simple and as low cost as possible.

Battery packs are built of many battery cells. We want to be able to monitor the performance of individual cells and dynamically switch out cells that develop faults. 

We want batteries to last for many years and for thousands of charge and discharge cycles without the need for maintenance or servicing.

So what are the problems with present state of the art batteries that need to be solved to gain the ultimate battery?

We know of battery chemistries that can store far more energy per unit of volume, or per unit of weight. We know of battery chemistries that could charge much faster.

We also know of other battery chemistries that can be charged and recharged almost indefinitely - but don't have many of the other desirable properties.

So why do batteries that have most of the properties that we want, fail to last very long? One of the biggest problems in our otherwise most potentially desirable batteries is that the volume of the anode or cathode changes as the battery charges up and then discharges. These volume changes soon start to break up the structure of the battery. Breaking up the anode or cathode. breaking up the important layers that form between anode and cathode that allow a rechargeable battery to function. Tesla already uses a matrix with some silicon oxide that allows a small amount of expansion and contraction to increase the life of a battery.

Researchers have discovered that it is possible to carefully control where this expansion and contraction takes place - and by creating tiny spaces within which nano grains of the electrode material can expand and contract, the bulk material no longer breaks up. Some researchers have created a sponge like matrix, others have created a matrix of tiny tubes of graphene, or a nano scale array of tubes of mixed ionic-electronic conductors.  The expansion and contraction of the lithium metal nanoparticles then takes place within these tubes without impacting the bulk structure of the electrode. An electrode using nano particles of silicon in a matrix that controls expansion is also distinctly possible. New designs for this matrix would allow the same mass of battery to hold a higher charge, and to charge faster, and to last much longer- without changing the battery chemistry.

Production of these batteries also requires new methods of producing uniform nano-scale particles of the electrode material to fit inside the sponge or tube matrix.

Creating nano-scale spaces in tubes or sponges for expansion and contraction within the battery is the key to solid state lithium batteries -where the expansion and contraction of existing prototypes cause them to break down within a few hundred cycles. I expect that we will hear that Tesla's team working on these solid batteries is now achieving thousands of cycles.

These expansion tolerant battery design will also allow rapid charging to a higher state of charge and discharge to much lower values without impacting the life of the batteries.

Another common problem is the nature of the layer that forms between the electrode and the electolyte. This layer needs to be stable and keep its structure through many thousands of charge and discharge cycles. In early designs of lithium metal batteries this layer was unstable and tended to grow needle like crystals of lithium that could cause the battery cell to fail. Some researchers have developed techniques to explore the structure of this interface and to design polymer composites that create a much more stable interface. Others  are developing solid ceramic electrolytes to perform the same function, for example using a nano layer of boron nitride. Both these polymer and ceramic composites can be designed to be non flammable, some even include a fire-retardant additive such as deca bromo diphenyl ethane , and can be solid state rather than liquid, avoiding the risk of batteries contributing to a fire in an accident.

Some researchers have been looking at the manufacturing methods for these new battery cell designs and have developed low cost methods of creating these new electrode and electrolyte designs, such as mixing the electrode nano particles together with the nano tubes in a water based slurry before forming the electrode layers and drying in vacuum.

I expect to hear from Tesla,  that use of new interface polymers is resulting in higher energy densities and stability over many more cycles of charge and discharge.

For the future, These techniques for using nano particles in the electrodes for controlling expansion and getting a much better understanding of the electrode /electrolyte interface are likely to speed up the development of other battery chemistries

Others to watch are lithium sulphur, sulphur bromine and potassium ion batteries.

More accurate and rapid temperature control of the battery pack is also likely to feature at Tesla battery day. Some Tesla patents for this have already been published and older patents abandoned.  Tesla has detailed records of the long term performance of its batteries and knows how few need replacing. One development we are likely to see is a dramatic simplification of the battery pack and its supporting structures. This could be the creation of the floor of the car as a single new casting that forms the cooling and heating plate and includes the cooling channels, and all the supporting structures for the individual cells, plus new wiring harnesses that simplifies connection and control of individual cells, doing away with the need for a separate battery pack casing and the battery modules and reducing the manufacturing costs.

In Tesla's recent patent each battery cell is insulated from the next. Heat from each cell is transferred from the cell to the cooling plate it sits on by hollow fins partially filled with a liquid. This liquid evaporates using heat from the cell and condenses against the cooling plate below. Liquid flowing through the channels in the cooling plate removes the heat. 

The direction of heat flow can be reversed by heating the fluid pumped through the basal plate, and the hollow fins will now efficiently transfer heat back to the cells.

Tesla plans to use a heat pump to heat or cool the circulating fluid and also to be able to store heat in a heat reservoir to increase the efficiency of the system.

More attention to rapid heating and cooling of the cells results in optimal battery temperatures for charging, for supplying the motors, and for cooling to the optimal temperatures when not active. Such a battery management system would use more energy, but result in much greater efficiencies overall and longer battery life, and optimal fast charge rates.

So in summary - we are likely to see all the desirable qualities of Tesla batteries enhanced, some quite dramatically. We are likely to see batteries that are cheaper to manufacture, charge faster, and last longer.

We are also likely to see numbers of new Tesla battery patents published at the same time.

Further reading:








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