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    Once again Stephane has written an excellent summary about the science of Lithium Ion batteries and raises a great question. Hopefully someone can answer

    stephane@disqus_XgstkgZcVY

    Perhaps we should ask ourselves, why most Li-ion batteries exhibit catastrophic failure when punctured.

    Most Li-Ion batteries don’t contain Lithium in metallic form. So, from where comes the issue?

    As soon as Lithium (in metallic form) meets the oxygen that’s in the ambient air, it forms an oxide layer (kind of passivization layer), and when this happens past a certain temperature, Lithium self ignites, and violently burns. Therefore, your eyes never see Lithium in metallic form. Your eyes see the oxide layer that’s instantly forming, when Lithium meets the ambient air containing Oxygen. Kind of instant rust.

    As soon as Lithium (in metallic form) meets water, it spontaneously heats up, dissociates water into hydrogen and oxygen, and violently burns because of the heat, and the spontaneous ignition possibility of the hydrogen and oxygen mix.

    But, as I wrote above, Most Li-Ion batteries don’t contain Lithium in metallic form.
    So, from where comes the issue?

    Before answering this, I would like to check if I’m okay with the understanding of what’s a Li-Ion battery.

    Most Li-Ion batteries contain Lithium that’s bonded or docked on other stuff like Carbon (C), Cobalt (Co) and Oxygen (O). Bonded is not the same as docked.
    By “bonded”, I mean a strong permanent chemical bond like covalent (HCl) or ionic (NaCl).
    By “docked” I mean a weak surface intercalation docking feature, kind of surface adsorption.

    Currently, surface chemistry, especially the surface intercalation docking chemistry, is a hot topic dealing with Hydrogen adsorption (for getting rid of big pressurized H2 bottles), Lithium cations or Sodium cations intercalation (for getting lighter batteries), and polyrotaxanes (for getting more robust batteries). The rings featured by polyrotaxanes rely on yet another kind of relatively weak surface bond, which is the particular surface bond exhibiting one degree of freedom, that led to the 2016 Nobel Prize in Chemistry “for the design and synthesis of molecular machines”.

    So, in a Li-ion battery, some percentage of Lithium gets permanently bonded to CoO2 (positive electrode) and C6 (negative electrode) for forming the bulk of both electrodes.
    The remaining percentage of Lithium shows as Lithium cations (positively charged ions) acting like heavy and bulky anti-electrons, kind of dense gas made of positively charged particles in case you like the electron gas analogy. There shall thus be an ionic current inside the battery, in one direction when the battery gets charged, and in the reverse direction when the battery gets discharged.

    The chemical formula of the electrodes surfaces depend on the amount of Lithium cations, having actually docked.

    The positive electrode surface is described as Li(x)CoO2
    The (x) tells how much Lithium is actually present. Part of the x is variable, depending on the amount of Lithium cations having docked.

    The negative electrode surface is described as Li(y)C6
    The (y) tells how much Lithium is actually present. Part of the y is variable, depending on the amount of Lithium cations having docked.

    I guess that x + y is a constant, as Lithium cations never escape from the battery.

    Lithium cations (positively charged), get dispersed as an ultra thin powder, forming a colloidal solution into a liquid or gel that’s not conducting electricity (otherwise the battery would self-discharge), this inside a 3D matrix that’s also non-conductive, exhibiting 50 nanometer wide holes and a 50% permeability, for allowing the Lithium cations (positively charged) to freely circulate inside such matrix, like a dense anti-electronic gas, while immobilizing the bigger liquid or gel molecules. Such is the “ionic center” inside a battery. Please note, the “ionic center” relies on a liquid or gel electrolyte acting as Lithium cations (positively charged) reservoir, and on a porous separator.

    The battery is thus a stack made of three layers :
    – the positive electrode whose active surface is described as Li(x)CoO2, where Li cations can dock and undock
    – the “ionic center” containing mobile Li cations (positively charged ions) acting as dense anti-electronic gas
    – the negative electrode whose active surface is described as Li(y)C6, where Li cations can dock and undock

    In order to produce the Lithium cations, a Lithium cations factory needs to exist within the battery, for the “ionic center” to remain densely populated after thousands of charge – discharge cycles, especially in case each charge – discharge cycle sees a proportion of Lithium cations getting neutralized when encountering some negative charge while travelling. One can rely on a redox arrangement. The most frequent redox arrangement is basing on copper (positive terminal) and aluminium (negative terminal). For the redox to work, some intermediate stuff must exist between the copper and the aluminium. You would expect Bleach over there (NaOCl in other words Sodium Hypochlorite) but wait a minute, we are not dealing with a primary cell here, so logically we want to avoid Hydrogen gas formation, electrode plating, electrode consumption, etc. So what to do ? Guess what we put as intermediate stuff : the above mentioned “ionic center”. Looks so bizarre. Currently I have no better way to explain. Can somebody please help?

    Considering the aluminium/copper redox necessity, the battery is thus a stack made of five layers :
    – the aluminium collector (positive terminal)
    – the positive electrode whose active surface is described as Li(x)CoO2, where Li cations can dock and undock
    – the “ionic center” containing mobile Li cations (positively charged ions) acting as dense anti-electronic gas
    – the negative electrode whose active surface is described as Li(y)C6, where Li cations can dock and undock
    – the copper collector (negative terminal)
    Is this correct?

    So, anyway, here is what’s supposed to happen inside a Li-ion battery, when charging it.

    Let’s see what’s supposed to happen at the negative terminal.

    The literature says everywhere like a parrot, that upon charging, the Lithium cations (positively charged) get attracted by electrostatics by the negative terminal, they intercalate on the negative electrode surface Li(y)C6, and the electrons coming from the charger, rush into the negative terminal of the battery.
    Such explanation doesn’t satisfy me. Here is why. Say we get electrons rushing into the negative terminal. Letting this happen, aren’t we neutralizing the Lithium cations ? What do they become, after getting neutralized? Lithium metal? How do they dis-intercalate doing the discharge, then? You see the problem? Can somebody please help?

    Let’s see what’s supposed to happen at the positive terminal.

    Such charging current can only exist in case at the exact same time, there is the exact same quantity of electrons, rushing out the positive terminal, going inside the charger. Such current duly exists, because during the charge, the Lithium cations (positively charged) get repelled by electrostatics by the positive terminal, and as consequence, they dis-intercalate from the positive electrode surface Li(x)CoO, and they contribute to the ionic current that’s occurring inside the “ionic center”, transferring Lithium cations (positively charged) to the negative electrode.
    Such explanation may satisfy me, because it bases on the electrostatic repulsion phenomenon. This allows the Lithium cations (positively charged) to remain intact, not mating with electrons. This makes me think about loading a kind of electrostatic spring. Can somebody please help?

    The charging process gets problematic as soon as one the three following conditions is met :
    – negative electrode surface getting fully intercalated
    – positive electrode surface getting fully dis-intercalated
    – no more Lithium cations remaining in the “ionic center”

    Once charged, we leave the battery unconnected.
    The literature says everywhere like a parrot, that the battery doesn’t self discharge because the “ionic center” embeds a porous separator, immobilizing everything that’s larger than 50 nanometer. I can imagine that 50 nanometer is wide enough for letting ultrafine Lithium cations (positively charged) pass through it. Albeit I’m asking if really, the Lithium cations are so fine, less than 50 nanometers tall. Are we absolutely sure that inside the “ionic center”, most Lithium cations are less than 50 nanometer tall? What’s the real purpose of the porous separator? What if the porous separator also blocks the Lithium cations, only letting some “electric propagation” to happen through “pure charges” ? Say there are positive electrons. Say they are our positive charges, freely circulating through the “ionic center”. Positive electrons, I know this sounds ridiculous. But wait a moment, as positive electron approximation, we have protons (H+). Amazing. I still don’t understand why a porous separator that’s blocking things larger than 50 nanometers, or only letting pass “pure positive charges” is going to prevent the battery from self discharging. I’m asking this here, because I want to avoid any misconception in my mind, about what’s a porous separator, and how it operates.

    Can somebody please help?

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