Patent Description:
The liquid electrolyte is usually used for the existing lithium ion secondary battery as a medium for the lithium ion transport. However, the volatile property of the liquid electrolyte may adversely affect the human body and the environment. Moreover, it is also a great security concern for the battery users due to the flammability of the liquid electrolyte.

Furthermore, one reason for the destabilization of lithium batteries is the greater surface activity of the negative electrode and the higher voltage of the positive electrode. When the liquid electrolyte is directly contacted to the electrodes, the interfaces therebetween is destabilized and the exothermic reaction is occurred to form a passivation layer. These reactions would consume the liquid electrolyte and the lithium ion and generate heat. When a local short circuit occurs, the local temperature rises rapidly. The passivation layer will become unstable and release heat. This exothermic reaction is cumulative to cause the temperature of the whole battery to continue to rise. The one of safety concerns of using a battery is that once the battery temperature is increased to a starting temperature (trigger temp. ), the thermal runaway is initiated to cause an ignition or explosion of the battery. That is a major safety issue for using.

In recent years, the solid electrolytes is a focusing research. The ionic conductivity of the solid electrolytes are similar to the ionic conductivity of the liquid electrolytes, without having the properties of evaporating and burning. Also, the interfaces between the solid electrolytes and the surface of active materials are relatively stable, regardless chemically or electrochemically. However, differing from the liquid electrolyte, the contact area between the solid electrolytes with the active materials is quite small, the contact surface is poor, and the charge transfer coefficient is low. So there is a problem that the charge transfer interface resistances of the active materials with the positive and negative electrodes are large. It is adverse for the efficient transmission of lithium ions. Therefore, it is still difficult to completely replace the liquid electrolytes by the solid electrolytes.

Moreover, for the negative electrode materials of the lithium ion batteries, the theoretical volumetric capacity of the conventional graphite carbon negative electrode materials is only <NUM> mAh/g, which limits the improvement of the energy density of the lithium ion batteries. While the volumetric capacity is up to <NUM> mAh/g, silicon is became the focus of current research. However, when elementary silicon is used as a negative electrode, a huge volume change (up to <NUM>%) would be occurred during the charging and discharging processes, which may easily lead to the formation of a void interface between the electrolyte and the elementary silicon to cause the continued decline in electrode performance.

Therefore, how to adapt solid electrolytes efficiently in large amount, while taking into account the improvement of the electrical capacity of the electrode layer, is an urgent problem to be solved in this art.

Relevant prior art is for example described in documents <CIT> and <CIT>.

It is an objective of this invention to provide an active material ball electrode layer structure to overcome the forgoing shortcomings. The dual-type electrolytes with different percentages or characteristics are utilized. Therefore, the problems of the high resistance of the charge transfer and small contact area, caused by the directly contact of the solid electrolyte and the active material, are eliminated. The amount of organic solvents is reduced, and the safety of the battery is improved.

Also, it is another objective of this invention to provide an active material ball electrode layer structure. The different percentages and characteristics configuration of the electrolytes inside and outside the active material balls is utilized. The void problems caused by the huge volume change of the active materials can be solved by the electrolytes inside of the active material balls, and the expansion resistance can be provided for the active materials by the electrolytes outside of the active material balls.

In order to implement the abovementioned, this invention discloses an active material ball electrode layer structure, which includes a plurality of active material balls and a second mixed electrolyte. The active material ball includes a plurality of active material particles, a first electrically conductive material, a first binder and a first mixed electrolyte. The active material balls and the different characteristics configuration of the first mixed electrolyte and the second mixed electrolyte are utilized. The void problems caused by the huge volume change of the active material particles can be solved by the first mixed electrolyte inside of the active material balls, and the expansion resistance can be provided for the active material balls by the second mixed electrolyte outside of the active material balls. In addition, the problems of the high resistance of the charge transfer and small contact area, caused by the directly contact of the solid electrolyte and the active material, are eliminated. Therefore, the better ion-conduction is achieved with improved safety.

Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

The present invention will become more fully understood from the detailed description given hereinbelow illustration only, and thus are not limitative of the present invention, and wherein:.

Please refer to <FIG>, which is a schematic diagram of the active material ball of this invention. As shown, the active material ball <NUM> is pre-formed as a sphere. The active material ball <NUM> includes a plurality of first active material particles <NUM>, a first electrically conductive material <NUM> and a first mixed electrolyte <NUM>. The average particle diameter D50 of the first active material particles <NUM> does not greater than <NUM>% of the diameter of the active material ball <NUM>. The volume change of the first active material particles <NUM> during extraction and insertion reactions is <NUM>% to <NUM>%.

Please also see <FIG>, which is a schematic diagram of the active material ball electrode layer structure of this invention. The active material ball electrode layer structure <NUM> of this invention is composed of the pre-formed active material ball <NUM>. A first mixed electrolyte <NUM> is located inside the active material ball <NUM>, and a second mixed electrolyte <NUM> is located outside the active material ball <NUM>. The first mixed electrolyte <NUM> is mainly composed of a deformable electrolyte, and the second mixed electrolyte <NUM> is mainly composed of an electrolyte with relatively lesser deformation ability than the deformable electrolyte of the first mixed electrolyte <NUM>. The average particle diameter D50 of the active material ball <NUM> does not greater than <NUM>% of a thickness of the electrode layer structure <NUM>. The electrolyte with relatively greater deformation is selected from a gel electrolyte, a liquid electrolyte, an ionic liquid, an ionic liquid electrolyte, a soft solid electrolyte or a combination thereof. The soft solid electrolyte is selected from a sulfide-based solid electrolyte, a hydride solid electrolyte, a halide based solid electrolyte, a polymer solid electrolyte or a combination thereof. The polymer solid electrolyte includes a polyethylene oxide (PEO), a polyvinylidene fluoride (PVDF), a polyacrylonitrile (PAN), a polymethylmethacrylate (PMMA) and a polyvinylchloride (PVC).

The sulfide-based solid electrolyte may be the Thio-LISICON (LixM1_x005FyM0yS<NUM>, where M is Si or Ge, M0 is P, Al, Zn, Ga or Sb), Li<NUM>-x005FxGe<NUM>-x005FxPxS<NUM>, Li<NUM>GeS<NUM>, Li<NUM>Zn<NUM>GeS<NUM>, Li<NUM>Ge<NUM>Ga<NUM>S<NUM>, Li<NUM>Ge<NUM>P<NUM>S<NUM>, Li<NUM>Si<NUM>P<NUM>S<NUM>, Li<NUM>Zn<NUM>Zr<NUM>S<NUM>, Li<NUM>P<NUM>S<NUM>, Li<NUM>SnS<NUM>, Li<NUM>GeP<NUM>S<NUM>, Li<NUM>Ge<NUM>Si<NUM>P<NUM>S<NUM>, Li<NUM>Si<NUM>P<NUM>S<NUM>Cl<NUM>, or the LGPS family such as Li<NUM>GeP<NUM>S<NUM>, Li<NUM>MP<NUM>S<NUM> (where M is Si4+ or Sn4+), Li<NUM>+dM<NUM>+dP<NUM>-x005FdS<NUM>(where M is Si4+ or Sn4+), or Li<NUM>Ge<NUM>-x005FxSnxP<NUM>S<NUM>, or argyrodite crystal system such as, Li<NUM>PS<NUM>X (where X is Cl, Br or I) or <NUM>(<NUM>. 75Li<NUM>S·<NUM>. 25P<NUM>S<NUM>)·33LiBH<NUM>, or thiophosphates type such as Li<NUM>PS<NUM>I or Li<NUM>P<NUM>S<NUM>I, or layered sulfide such as Li3x[LixSn<NUM>-x005FxS<NUM>], Li<NUM>Sn<NUM>S<NUM>, Li<NUM>SnS<NUM> or Li<NUM>tLi<NUM>Sn<NUM>S<NUM>]. The borohydride based solid electrolyte may be LiBH<NUM>-LiI (-LiNH<NUM>; -P<NUM>I<NUM>; -P<NUM>S<NUM>).

Excepting for the above-mentioned materials, the polymer solid electrolyte may also be PEO-LiX(where X is ClO<NUM>, PF<NUM>, BF<NUM>, N(SO<NUM>CF<NUM>)<NUM>), PEO-LiCF<NUM>SO<NUM>, PEO-LiTFSI, PEO-LiTFSI-Al<NUM>O<NUM> Composite solid polymer, PEO-LiTFSI-<NUM>% TiO<NUM> Composite solid polymer, PEO-LiTFSI-<NUM>% HNT Composite solid polymer, PEO-LiTFSI-<NUM>% MMT Composite solid polymer, PEO-LiTFSI-<NUM>% LGPS Composite solid polymer, PEO-LiClO<NUM>-LAGP, or Poly(ethylene glycol) diacrylate (PEGDA), Poly(ethylene glycol) dimethacrylate (PEGDMA), Poly(ethylene glycol) monomethylether (PEGME), Poly(ethylene glycol) dimethylether (PEGDME), poly[ethylene oxide-co-<NUM>-(<NUM>-methoxyethoxy)ethyl glycidyl ether] (PEO/MEEGE), Poly(ethyl methacrylate) (PEMA), poly(oxyethylene), poly (cyanoacrylate) (PCA), Polyethylene glycol (PEG), Poly(vinyl alcohol) (PVA), Polyvinyl butyral (PVB), Poly(viny chloride) (PVC), PVC-PEMA, PEO-PMMA, Poly(acrylonitrile-co-methyl methacrylate) P(AN-co-MMA), PVA-PVdF, PAN-PVA, PVC-PEMA, or hyperbranched polymers such as poly[bis(triethylene glycol)benzoate], or polycarbonates such as poly(ethylene oxide-co-ethylene carbonate) (PEOEC), Polyhedral oligomeric silsesquioxane (POSS), Polyethylene carbonate (PEC) , poly (propylene carbonate) (PPC), poly(ethyl glycidyl ether carbonate) (P(Et-GEC), poly(t-butyl glycidyl ether carbonate) P(tBu-GEC), or cyclic carbonates such as poly (trimethylene carbonate) (PTMC), or polysiloxane-based such as Polydimethylsiloxane (PDMS), poly(dimethyl siloxane-co-ethylene oxide) P(DMS-co-EO), Poly(siloxane-g-ethyleneoxide), or plastic crystal electrolytes (PCEs) such as succinonitrile (SN), PEO/SN, ETPTA/SN , PAN/PVA-CN/SN, or polyesters such as ethylene adipate, ethylene succinate, ethylene malonate, or polynitriles such as polyacrylonitrile (PAN), poly(methacrylonitrile) (PMAN), poly(N-<NUM>-cyanoethyl)ethyleneamine (PCEEI), Poly(vinylidenedifluoridehexafluoropropylene) (PvdF-HFP), Poly(vinylidenedifluoride) (PvdF), Poly(ε-caprolactone) (PCL).

The electrolyte with relatively lesser deformation is selected from the solid electrolyte with higher hardness (inherently lower fracture toughness), such as an oxide-based solid electrolyte and its fracture toughness is approximately <NUM> MPa. The oxide-based solid electrolyte is a lithium lanthanum zirconium oxide (LLZO) electrolyte or a lithium aluminum titanium phosphate (LATP) electrolyte and their derivatives. Generally, the description of the electrolyte materials with relatively greater deformation or relatively lesser deformation is only for illustration, and is not intended to limit the present invention to these electrolytes with the relatively greater deformation or the relatively lesser deformation. The above-defined relatively greater deformation and relatively lesser deformation refer to the deformation that the electrolytes can be recoverable to the original situation after deforming. For example, if the fragmentation is occurred during deforming, it has to be called irrecoverable. That should not be within the scope of relatively greater deformation and relatively lesser deformation defined in this invention.

When the first mixed electrolyte <NUM> is selected from a gel electrolyte, a liquid electrolyte, or an ionic liquid, the first mixed electrolyte <NUM> is extruded by the first active material particles <NUM> caused by the expansion during the charging and discharging processes. Therefore, the first mixed electrolyte <NUM> would be slightly extruded from the active material ball <NUM>. When the volume contraction of the first active material particles <NUM> is occurred, the first mixed electrolyte <NUM> would be sucked into the active material ball <NUM>. Therefore, during the whole charging and discharging processes, the void will not be occurred and the derived void problems would be happened. When the first mixed electrolyte <NUM> is a soft solid electrolyte, the squeezed first mixed electrolyte <NUM> will form a buffer zone due to the elasticity of the soft solid electrolyte. Additionally, if the proportion of the soft solid electrolyte in the first mixed electrolyte <NUM> is higher, it can also constraint the active material particles <NUM>.

The second mixed electrolyte <NUM> is disposed outside of the active material balls <NUM> and filled the gaps between the active material balls <NUM> to be against the outer surfaces of the active material balls <NUM>. Due to the second mixed electrolyte <NUM> is mainly composed of an electrolyte with relatively lesser deformation, it can form a resistance to volume expansion of the active material balls <NUM>. When it is configured, the second mixed electrolyte <NUM> may intersect or partially invade the boundary of the active material balls <NUM>. As shown in figures, the active material balls <NUM> are only for illustration, and does not limit the boundary thereof is maintained such a complete state. The second mixed electrolyte <NUM> depicted in the figures is also only for illustration, not to limit its position, size, distribution, etc..

The first mixed electrolyte <NUM> may also include the electrolyte with relatively lesser deformation, and the second mixed electrolyte <NUM> may also include the electrolyte with relatively greater deformation, but with different volume contents. For example, the volume content of the electrolyte with relatively greater deformation of the first mixed electrolyte <NUM> is greater than <NUM>% of the total volume content of the first mixed electrolyte <NUM>, preferably is greater than <NUM>%. The volume content of the electrolyte with relatively lesser deformation of the second mixed electrolyte <NUM> is greater than <NUM>% of the total volume content of the second mixed electrolyte <NUM>, preferably is greater than <NUM>%.

Therefore, by the different percentages and characteristics configuration of the electrolytes inside and outside the active material balls <NUM>, the expansion resistance can be provided for the active material balls <NUM>. Also, the contact area and condition of the active material particles and the electrolytes are maintained in a better status, and the void problems caused by the huge volume change of the active material particles can be solved.

In order to make the aforementioned active material balls <NUM> more clear, the following description only illustrates one possible manufacturing process. When the first mixed electrolyte <NUM> is in liquid, firstly, the active material particles <NUM>, the first electrically conductive material <NUM> and the first binder (not shown in the figure) are mixed with a solvent and then coated on the temporary substrate. The temporary substrate is removed after successively drying and removing the solvent, and then crushing and using ball milling to obtain the active material balls <NUM>. In the meantime, when the solvent is removed, the holes formed in the active material balls <NUM> are roughly irregular in shape. The first mixed electrolyte <NUM> can be filled in the holes.

Since the holes have to be filled with electrolytes, the first mixed electrolyte <NUM> is mainly composed of the electrolyte with relatively greater deformation to fill the spaces of the holes easily. By the characteristics of soft and deformable, the electrolyte can be deformed according to the size or the shape of the holes. Therefore, the electrolyte can be definitely filled in the holes to ensure the contact state of the first mixed electrolyte <NUM> and the active materials particles <NUM>. Also, when the first mixed electrolyte <NUM> is mainly composed of the soft solid electrolyte, the soft solid electrolyte may be mixed directly to the active material particles <NUM>, the first electrically conductive material <NUM> and the first binder.

The first active material particles <NUM> is selected a lithium metal, a carbon material, a silicon based materials, such as a silicon and/or a silicon oxide, or a combination thereof, which may have volume change during the electrochemical reactions. The first binder is used to fix their relative positions or can be selected, adjusted or modified according to the characteristics of different active materials to solve the derived problems. For example, in the case of the silicon and/or the silicon oxide as the active materials, in order to control the volume expansion during charging and discharging processes, the first binder mainly includes a cross-linked polymer. The volume content of the cross-linked polymer in the first binder is greater than <NUM>%. Also, with a higher proportion of the first electrically conductive material <NUM> and the first binder, it can provide sufficient high expansion constraint force and electrical conductivity.

In the conventional electrode layer (in the example where silicon and/or silicon oxide (Si/SiOx) and graphite are directly mixed), the volume content of the electrically conductive material is about <NUM>%, the volume content of the binder is about <NUM>%, and the volume content of the active materials, including silicon and/or silicon oxide (Si/SiOx) and graphite, is about <NUM>%. However, in this invention, the volume content of the first electrically conductive material <NUM> in the active material balls <NUM> is <NUM>% to <NUM>%, and the volume content of the first binder in the active material balls <NUM> is <NUM>% to <NUM>%. Therefore, with a higher amount of the first binder, whose main component is a cross-linked polymer, it can greatly increase the expansion constraint force to effectively control the huge volume change of the silicon material during charging and discharging processes.

The first electrically conductive material <NUM> may include an artificial graphite, a carbon black, an acetylene black, a graphene, a carbon nanotube, a vapor grown carbon fiber (VGCF) or a combination thereof. The carbon nanotube and the VGCF can not only be used as electrically conductive materials, but also have the ability to absorb electrolyte and elastic deformation. The first binder is mainly a cross-linked polymer with strong physical or chemical adhesion. Therefore, the first binder has less elasticity. For example, the first binder may also have good electron donor with acid group, including polyimide (PI), acrylic resin, epoxy, or a combination thereof. With above-mentioned higher amount of the binder, the first binder with strong rigidity can be used to constraint the active material particles to control the expansion scale of the active material particles after charging and discharging. Therefore, the irrecoverable void zone would be controlled or eliminated.

The higher amount of the rigid first binder and the first electrically conductive material <NUM> will reduce the bending ability, and also limit to reduce the ratio of the remaining active materials. Therefore, the specific capacity will be reduced. However, the active material ball <NUM> of the present invention is only served as part of the active materials in the electrode layer structure, there are no such concerns, that is, these defects will not affect the electrode layer structure of this invention, which will be described in detail later.

Please return to <FIG>, the pre-formed active material balls <NUM> and the second binder are mixed to form the active material ball electrode layer structure <NUM>. The second binder is different from the first binder. For example, the first binder is mainly composed of the rigid binder to control the volume change of the active material balls <NUM>. Therefore, the elasticity of the first binder is poor. The second binder is selected the binder with good elasticity. Therefore, the elasticity of the second binder is better than the elasticity of the first binder. The second binder is mainly composed of the linear polymer with good elasticity, including Polyvinylidene fluoride (PVDF), Polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), styrene-butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC), to maintain the flexibility of the active material ball electrode layer structure <NUM>. The material characteristics of PVDF, PVDF-HFP, SBR have a sponge-like structure that can have a high ability to absorb electrolyte.

The second binder, the second electrically conductive material <NUM> and the second mixed electrolyte <NUM> are mixed between the active material balls <NUM>, i.e. outside of the active material balls <NUM>. The second mixed electrolyte <NUM> is far away from the first active material particles <NUM> than the first mixed electrolyte <NUM> of the active material balls <NUM>.

Compared to the requirements of the first mixed electrolyte <NUM>, which emphasizes larger contact surface of the active material particles <NUM> to obtain high charge transfer, the requirements of the second mixed electrolyte <NUM>, which far away from the active material particles <NUM>, for effective contact area is lesser. Therefore, the second mixed electrolyte <NUM> is mainly composed of the electrolyte with relatively lesser deformation. In addition to greatly reducing the amount of organic solvent, the gel and the liquid electrolyte, it has better thermal stability and heat dissipation performance to maintain safety continuously. Also, the electrolyte with relatively lesser deformation can constraint the active material balls <NUM>. That means that the electrolyte with relatively lesser deformation, such as a hard solid electrolyte, is used to limit or resist the deterioration of the internal distribution of the active material balls <NUM> caused by the expansion of the internal active material particles <NUM>, especially the volume shrinkage and expansion during the charging and discharging cycle. Further, due to the requirements for effective contact area is lesser, the electrolyte with relatively lesser deformation can be used to preform the ion conduction to allow the lithium ions to perform high speed and bulk transport between the electrolyte with relatively lesser deformation and the active material balls or between the electrolytes with relatively lesser deformation. The composition of the electrolyte with relatively lesser deformation and the electrolyte with relatively greater deformation can be the same as described above, and the process of forming or filling is also the same, and will not be repeated here.

Please refer to <FIG>, there have a plurality of second active material particles <NUM> and the second electrically conductive material <NUM> disposed among the active material balls <NUM>. The second electrically conductive material <NUM> may include an artificial graphite, a carbon black, an acetylene black, a graphene, a carbon nanotube, a vapor grown carbon fiber (VGCF) or a combination thereof. The composition of the first electrically conductive material <NUM> and the second electrically conductive material <NUM> are the same or different. The second active material particles <NUM> has to be selected according to the properties of the active material balls <NUM>. The material characteristic of the second active material particles is different from the material characteristic of the first active material particles <NUM>.

Furthermore, the active material balls <NUM> may include a plurality of third active material particles <NUM>, showing in <FIG>. The composition of the third active material particles <NUM> and the first third active material particles <NUM> are the same or different.

Claim 1:
An active material ball electrode layer structure, comprising:
a plurality of active material balls, each of the active material balls includes a plurality of first active material particles, a first electrically conductive material, a first binder and a first mixed electrolyte; and
a second mixed electrolyte, disposed outside of the active material balls and filled gaps between the active material balls to be against an outer surface of the active material balls to form a resistance of volume expansion of the active material balls;
wherein the first mixed electrolyte is mainly composed of an electrolyte, and the second mixed electrolyte is mainly composed of an electrolyte with relatively lesser deformation ability comparing to the mainly electrolyte of the first mixed electrolyte.