Patent Description:
In recent years, as a secondary battery having high output and high energy density, a non-aqueous electrolyte secondary battery that performs charging and discharging by moving lithium ions between a positive electrode and a negative electrode has been widely used.

There is a nail penetration test as a safety evaluation test for confirming resistance to an internal short circuit of a battery. The nail penetration test is, for example, a test in which a nail penetrates into a battery to simulatively generate an internal short circuit and a degree of heat generation is examined to confirm safety of the battery. It is important to suppress the heat generation of the battery at the time of the nail penetration from the viewpoint of securing the safety of the battery.

For example, Patent Literature <NUM> discloses a technique for suppressing heat generation of a battery in a nail penetration test by disposing a coating layer containing a functional material selected from a phosphorus-containing compound, a nitrogen-containing compound, and an inorganic silicon compound on a surface of an electrode plate of a positive electrode or a negative electrode.

For example, Patent Literature <NUM> discloses a technique for suppressing an increase in temperature at the time of abnormal heat generation of a battery by disposing an intermediate layer containing polyphosphate between a positive electrode and a negative electrode.

When a coating layer of a functional material or an intermediate layer of polyphosphate is disposed on a surface of an electrode plate as in Patent Literatures <NUM> and <NUM>, there is a problem that these layers become resistors and resistance of the battery is increased.

An electrode for a non-aqueous electrolyte secondary battery according to an aspect of the present disclosure includes a current collector, an active material layer that is formed on the current collector, and an aggregate of filler particles that is present in an island shape on a surface of the active material layer. The filler particles are compound particles containing at least one of phosphorus, silicon, boron, nitrogen, potassium, sodium, and bromine, and a transformation point of the filler particle at which the filler particle is transformed from a solid phase into a liquid phase or is thermally decomposed is in a range of <NUM> to <NUM>,<NUM>.

A non-aqueous electrolyte secondary battery according to an aspect of the present disclosure includes a positive electrode and a negative electrode, and at least one of the positive electrode and the negative electrode is the electrode for a non-aqueous electrolyte secondary battery.

According to the present disclosure, it is possible to suppress heat generation of a battery in a nail penetration test while suppressing an increase in battery resistance.

<FIG> is a schematic cross-sectional view illustrating an example of a configuration of an electrode according to the present embodiment. An electrode <NUM> illustrated in <FIG> is an electrode for a non-aqueous electrolyte secondary battery, and is applied to at least one of a positive electrode and a negative electrode of a non-aqueous electrolyte secondary battery.

The electrode <NUM> illustrated in <FIG> includes a current collector <NUM>, an active material layer <NUM> that is formed on the current collector <NUM>, and an aggregate <NUM> of filler particles that is present in an island shape on a surface of the active material layer <NUM>. That is, a surface structure of the electrode <NUM> is a sea-island structure having a sea region of the surface of the active material layer and an island region of the aggregate <NUM> of filler particles. The aggregate <NUM> is an aggregation of a single or a plurality of filler particles.

The filler particles constituting the aggregate <NUM> are compound particles containing at least one of phosphorus, silicon, boron, nitrogen, potassium, sodium, and bromine, and a transformation point of the filler particle at which the filler particle is transformed from a solid phase into a liquid phase or is thermally decomposed is in a range of <NUM> to <NUM>,<NUM>.

By using the electrode for a non-aqueous electrolyte secondary battery according to the present embodiment, an increase in battery temperature in a nail penetration test is suppressed. This mechanism is not sufficiently clear, but the following is presumed. Due to heat generation of the battery at the time of the nail penetration test, that is, heat generation of the battery when a nail penetrates into the battery and an internal short circuit is simulatively generated, the filler particles constituting the aggregate <NUM> are transformed from a solid phase into a liquid phase and flow on the surface of the active material layer <NUM>, or extend on the surface of the active material layer <NUM> by thermal decomposition and become a coating film covering the surface of the active material layer <NUM>. The coating film functions as a resistor component, and thus, the amount of short circuit current flowing between the positive and negative electrodes through the nail is suppressed. As a result, an increase in battery temperature in the nail penetration test is also suppressed. The formation of the coating film after the transformation of the filler particles into the liquid phase depends on the type of filler particle, and is performed by, for example, an increase in temperature higher than a melting point of a filler material, a thermal fusion reaction, a dehydration condensation reaction, a thermal polymerization reaction, or the like.

In addition, according to the electrode for a non-aqueous electrolyte secondary battery according to the present embodiment, an increase in battery resistance is suppressed. In normal use in which abnormal heat generation does not occur in a battery, since the aggregate <NUM> of filler particles is a material having low lithium ion conductivity, in a case where the aggregate <NUM> is present in a layer shape, movement of lithium ions is inhibited and an increase in battery resistance is caused. However, in the present embodiment, since the aggregate <NUM> has an island shape, a gap exists between the aggregates <NUM>, and ions such as lithium ions can easily pass through the gap. Therefore, it is considered that since lithium ions smoothly move between the positive and negative electrodes during charging and discharging of the battery as compared with a case where the entire surface of the active material layer <NUM> is covered with a coating layer of filler particles without a gap, an increase in battery resistance is suppressed.

Hereinafter, a constituent material of the electrode <NUM> will be described in more detail.

The filler particles are compound particles containing at least one of phosphorus, silicon, boron, nitrogen, potassium, sodium, and bromine and are not particularly limited as long as a transformation point of the filler particle at which the filler particle is transformed from a solid phase into a liquid phase or is thermally decomposed is in a range of <NUM> to <NUM>,<NUM>. A material of the filler particle include a phosphoric acid compound, a silicic acid compound, a boric acid compound, a melamine compound, a potassium salt compound, and a sodium salt compound. Examples of the phosphoric acid compound include metal phosphates such as phosphate-lithium salt, phosphate-sodium salt, phosphate-potassium salt, phosphate-calcium salt, phosphate-magnesium salt, and aluminum phosphate, condensed phosphates such as ammonium polyphosphate, sodium tripolyphosphate, and melamine polyphosphate, and phosphoric acid esters such as trimethyl phosphate and triphenyl phosphate. Examples of the boric acid compound include metal borates such as borate-sodium salt, borate-potassium salt, borate-calcium salt, borate-magnesium salt, aluminum borate, and melamine borate, boric acid esters such as trimethyl borate, boron oxide, and condensed borate. Examples of the silicic acid compound include metal silicate such as silicate-sodium salt, silicate-potassium salt, silicate-calcium salt, silicate-magnesium salt, silicate-barium salt, and silicate-manganese salt. Examples of the melamine compound include melamine cyanurate, melamine pyrophosphate, ethylene dimelamine, trimethylene dimelamine, tetramethylene dimelamine, hexamethylene dimelamine, and <NUM>,<NUM>-hexylene dimelamine. Examples of the potassium salt compound include potassium pyrosulfate (K<NUM>S<NUM>O<NUM>), potassium citrate monohydrate (C<NUM>H<NUM>K<NUM>O<NUM>•H<NUM>O), and potassium carbonate. Examples of the sodium salt compound include sodium carbonate. Among them, melamine polyphosphate, ammonium polyphosphate, sodium tripolyphosphate, sodium silicate, sodium borate, potassium citrate monohydrate, lithium metaphosphate, potassium dihydrogen phosphate, melamine cyanurate, potassium pyrosulfate, boron oxide, ethylene-<NUM>,<NUM>-bis(pentabromophenyl), ethylenebistetrabromophthalimide, potassium carbonate, and sodium carbonate are preferable.

The transformation point of the filler particle may be in a range of <NUM> to <NUM>,<NUM> and is preferably in a range of <NUM> to <NUM> so that the filler particle is appropriately transformed from a solid phase into a liquid phase or is thermally decomposed due to heat generation of the battery in the nail penetration test.

A covering rate of the aggregate <NUM> to the surface of the active material layer <NUM> is preferably <NUM>% or less, and more preferably <NUM>% or less, from the viewpoint of suppressing an increase in battery resistance. In addition, the covering rate of the aggregate <NUM> to the surface of the active material layer <NUM> is preferably <NUM>% or more from the viewpoint of suppressing an increase in battery temperature in the nail penetration test. As the covering rate is increased, the formation time of the coating layer covering the surface of the active material layer <NUM> during heat generation of the battery is shortened, but an optimum configuration is required according to the purpose because the battery resistance is increased. The covering rate of the aggregate <NUM> is calculated as follows.

The covering rate is determined by performing element mapping of the electrode surface by energy dispersive X-ray spectrometry (SEM-EDX) or the like. For example, a ratio of an area of the island region to a total area of the island region and the sea region is calculated by distinguishing the island region of the aggregate <NUM> and the sea region of the surface of the active material layer by element mapping. As an accuracy of the element mapping, when there is an uncovered region of about <NUM> square, it is possible to discriminate between the sea region and the island region.

The number of the aggregates <NUM> having an area of <NUM>,<NUM><NUM> or less is preferably <NUM>% or more and preferably <NUM>% or more with respect to the total number of the aggregates <NUM>. As the number of the aggregates <NUM> having an area of <NUM>,<NUM><NUM> or less is increased, the number of the gaps between the aggregates <NUM>, which are paths through which ions such as lithium ions easily pass, is increased in a wide range in a more uniform form, and thus, an increase in battery resistance can be suppressed.

The number of the aggregates <NUM> is preferably <NUM> or more and more preferably <NUM> or more per <NUM><NUM>. As the amount of the filler particles constituting the aggregate <NUM> is increased, the surface of the active material layer <NUM> is quickly covered by transformation of the filler particle from a solid phase into a liquid phase or thermal decomposition due to the heat generation of the battery at the time of the nail penetration test, and thus, an increase in battery temperature in the nail penetration test can be effectively suppressed.

An average particle diameter of the filler particles constituting the aggregate <NUM> is preferably <NUM> to <NUM>, and is more preferably in a range of <NUM> to <NUM>. The average particle diameter of the filler particles is determined as follows. First, <NUM> filler particles are randomly selected from an SEM image of the electrode surface. Next, grain boundaries of the selected <NUM> filler particles are observed, an outer shape of the filler particle is specified, an area of each of the <NUM> filler particles is determined, and the average particle diameter of the filler particles is calculated from an average value thereof.

The aggregate <NUM> may contain a binder in addition to the filler particles described above. By containing the binder, a binding property between the filler particles or a binding property between the filler particles and the current collector <NUM> can be improved. The binder is not particularly limited, and examples thereof include polyvinylidene fluoride (PVdF), ethylene dimethacrylate, allyl methacrylate, t-dodecyl mercaptan, α-methylstyrene dimer, and methacrylic acid. Polyvinylidene fluoride (PVdF), ethylene dimethacrylate, allyl methacrylate, t-dodecyl mercaptan, α-methylstyrene dimer, and methacrylic acid can allow the electrode <NUM> to adhere to a separator <NUM> by applying a pressure and/or heat to the aggregate <NUM>. In addition, the aggregate <NUM> may contain compound particles in addition to the filler particles described above. Examples of the compound particles in addition to the filler particles described above include inorganic particles formed of alumina, boehmite, titania, and the like.

In a case where the electrode <NUM> is used as a positive electrode, as the current collector <NUM> to be a positive electrode current collector, for example, a foil of a metal stable in a potential range of the positive electrode, such as aluminum, a film in which the metal is disposed on a surface layer, or the like can be used. In addition, it is preferable that the active material layer <NUM> to be a positive electrode active material layer contains a positive electrode active material and contains a conductive agent or a binder.

Examples of the positive electrode active material include lithium-transition metal composite oxides. Specifically, lithium cobaltate, lithium manganate, lithium nickelate, lithium nickel manganese composite oxide, lithium nickel cobalt composite oxide, and the like can be used, and Al, Ti, Zr, Nb, B, W, Mg, Mo, and the like may be added to these lithium-transition metal composite oxides.

As the conductive agent, carbon powders such as carbon black, acetylene black, Ketjen black, and graphite may be used alone or in combination of two or more thereof.

Examples of the binder include a fluorine-based resin such as polytetrafluoroethylene (PTFE) or polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), a polyimide-based resin, an acrylic resin, and a polyolefin-based resin. These binders may be used alone or in combination of two or more thereof.

An example of a method for producing a positive electrode will be described. First, a positive electrode mixture slurry containing a positive electrode active material, a binder, a conductive agent, a solvent, and the like is applied onto a positive electrode current collector, and the coating film is dried and then compressed, thereby forming a positive electrode active material layer on the positive electrode current collector. Next, a filler slurry containing filler particles, a binder, a solvent, and the like is prepared. Then, the prepared filler slurry is sprayed, dropped, transferred, or applied to the positive electrode active material layer, and drying is performed to form an aggregate of filler particles that is present in an island shape on a surface of the positive electrode active material layer. Examples of the solvent contained in the slurry include water, N-methyl-<NUM>-pyrrolidone (NMP), and ethanol.

The island-shaped aggregate is obtained by, for example, adjusting the amounts of the filler particles and the solvent contained in the filler slurry and controlling the spray amount, the dropping amount, or the applied amount of the filler slurry. In addition, the island-shaped aggregate can also be obtained by, for example, disposing a masking sheet or the like provided with a plurality of through-holes having a predetermined size on the positive electrode active material layer, and spraying, dropping, or applying the filler slurry from above the disposed masking sheet.

In a case where the electrode <NUM> is used as a negative electrode, as the current collector <NUM> to be a negative electrode current collector, for example, a foil of a metal stable in a potential range of the negative electrode, such as copper, a film in which the metal is disposed on a surface layer, or the like can be used. In addition, it is preferable that the active material layer <NUM> to be a negative electrode active material layer contains a negative electrode active material and contains a binder and the like.

As the negative electrode active material, a carbon material capable of occluding and releasing lithium ions can be used, and in addition to graphite, non-graphitizable carbon, graphitizable carbon, fibrous carbon, coke, carbon black, and the like can be used. Furthermore, as a non-carbon-based material, silicon, tin, and a metal or an oxide mainly containing silicon and tin can be used.

Examples of the binder include a fluorine-based resin, PAN, a polyimide-based resin, an acrylic resin, a polyolefin-based resin, styrene-butadiene rubber (SBR), nitrile-butadiene rubber (NBR), carboxymethyl cellulose (CMC) or a salt thereof, polyacrylic acid (PAA) or a salt thereof (PAA-Na, PAA-K, and the like, or a partially neutralized salt may be used), and polyvinyl alcohol (PVA). These binders may be used alone or in combination of two or more thereof.

An example of a method for producing a negative electrode will be described below. First, a negative electrode mixture slurry containing a negative electrode active material, a binder, a solvent, and the like is applied onto a negative electrode current collector, and the coating film is dried and then compressed, thereby forming a negative electrode active material layer on the negative electrode current collector. Next, a filler slurry containing filler particles, a binder, a solvent, and the like is sprayed, dropped, or applied to the negative electrode active material layer, and drying is performed to form an aggregate of filler particles that is present in an island shape on a surface of the negative electrode active material layer. A method for obtaining an island-shaped aggregate is as described above.

Hereinafter, an example of the non-aqueous electrolyte secondary battery according to the present embodiment will be described.

<FIG> is a schematic cross-sectional view illustrating a non-aqueous electrolyte secondary battery as an example of an embodiment. A non-aqueous electrolyte secondary battery <NUM> illustrated in <FIG> includes a wound electrode assembly <NUM> formed by wounding a positive electrode <NUM> and a negative electrode <NUM> with a separator <NUM> interposed therebetween, a non-aqueous electrolyte, insulating plates <NUM> and <NUM> that are disposed on upper and lower sides of the electrode assembly <NUM>, respectively, and a battery case <NUM> housing the members. The battery case <NUM> includes a bottomed cylindrical case main body <NUM> and a sealing assembly <NUM> for closing an opening of the case main body <NUM>. Instead of the wound electrode assembly <NUM>, another form of an electrode assembly such as a stacked electrode assembly in which a positive electrode and a negative electrode are alternately stacked with a separator interposed therebetween may be applied. In addition, examples of the battery case <NUM> include a metal case having a cylindrical shape, a square shape, a coin shape, a button shape, or the like, and a resin case formed by laminating resin sheets (so-called laminate type resin case).

The case main body <NUM> is, for example, a bottomed cylindrical metal container. A gasket <NUM> is provided between the case main body <NUM> and the sealing assembly <NUM> to secure a sealing property of the inside of the battery. The case main body <NUM> has, for example, a projection part <NUM> in which a part of a side part thereof projects inside for supporting the sealing assembly <NUM>. The projection part <NUM> is preferably formed in an annular shape along a circumferential direction of the case main body <NUM>, and supports the sealing assembly <NUM> on an upper surface thereof.

The sealing assembly <NUM> has a structure in which a filter <NUM>, a lower vent member <NUM>, an insulating member <NUM>, an upper vent member <NUM>, and a cap <NUM> are sequentially stacked from the electrode assembly <NUM> side. Each member constituting the sealing assembly <NUM> has, for example, a disk shape or a ring shape, and the respective members except for the insulating member <NUM> are electrically connected to each other. The lower vent member <NUM> and the upper vent member <NUM> are connected to each other at the respective central parts thereof, and the insulating member <NUM> is interposed between the respective circumferential parts of the vent members <NUM> and <NUM>. When the internal pressure of the secondary battery <NUM> is increased by heat generation due to an internal short circuit or the like, for example, the lower vent member <NUM> is deformed so as to push the upper vent member <NUM> up toward the cap <NUM> side and is broken, and thus, a current pathway between the lower vent member <NUM> and the upper vent member <NUM> is cut off. When the internal pressure is further increased, the upper vent member <NUM> is broken, and gas is discharged through the opening of the cap <NUM>.

In the non-aqueous electrolyte secondary battery <NUM> illustrated in <FIG>, a positive electrode lead <NUM> attached to the positive electrode <NUM> extends through a through-hole of the insulating plate <NUM> toward a side of the sealing assembly <NUM>, and a negative electrode lead <NUM> attached to the negative electrode <NUM> extends through the outside of the insulating plate <NUM> toward the bottom side of the case main body <NUM>. The positive electrode lead <NUM> is connected to a lower surface of the filter <NUM> that is a bottom plate of the sealing assembly <NUM> by welding or the like, and the cap <NUM> that is a top plate of the sealing assembly <NUM> electrically connected to the filter <NUM> becomes a positive electrode terminal. The negative electrode lead <NUM> is connected to a bottom inner surface of the case main body <NUM> by welding or the like, and the case main body <NUM> becomes a negative electrode terminal.

The electrode <NUM> is applied to at least one of the positive electrode <NUM> and the negative electrode <NUM>. For the separator <NUM>, a porous sheet having an ion permeation property and an insulation property is used. Specific examples of the porous sheet include a fine porous thin film, a woven fabric, and a non-woven fabric. As a material of the separator <NUM>, an olefin-based resin such as polyethylene or polypropylene, cellulose, and the like are preferable. The separator <NUM> may be a laminate including a cellulose fiber layer and a thermoplastic resin fiber layer formed of an olefin-based resin or the like. In addition, a multi-layer separator including a polyethylene layer and a polypropylene layer may be used, or a separator obtained by applying a material such as an aramid-based resin or ceramic onto a surface of the separator <NUM> may be used.

The non-aqueous electrolyte contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. As the non-aqueous solvent, for example, esters, ethers, nitriles, amides, a mixed solvent of two or more thereof, and the like are used. The non-aqueous solvent may contain a halogen-substituted solvent in which at least some hydrogens in these solvents are substituted with halogen atoms such as fluorine. As the electrolyte salt, for example, a lithium salt such as LiPF<NUM> is used.

<NUM> parts by weight of a positive electrode active material represented by LiNi<NUM>Co<NUM>Al<NUM>O<NUM>, <NUM> part by weight of acetylene black (AB), and <NUM> part by weight of polyvinylidene fluoride (PVdF) were mixed, and an appropriate amount of N-methyl-<NUM>-pyrrolidone (NMP) was further added, thereby preparing a positive electrode mixture slurry. Next, the positive electrode mixture slurry was applied onto both surfaces of a positive electrode current collector formed of an aluminum foil, and the positive electrode current collector was dried. The positive electrode current collector was cut into a predetermined electrode size and was rolled using a roller to form a positive electrode active material layer on the both surfaces of the positive electrode current collector. Next, <NUM> parts by weight of melamine polyphosphate particles and <NUM> part by weight of polyvinylidene fluoride (PVdF) were mixed, and <NUM> of N-methyl-<NUM>-pyrrolidone (NMP) was further added, thereby preparing a filler slurry. <NUM> of the filler slurry was applied onto the positive electrode active material layer at a Wet film thickness equivalent to <NUM>, and the positive electrode active material layer was dried. The positive electrode active material layer was used as a positive electrode of Example <NUM>.

When a surface of the positive electrode of Example <NUM> was observed by SEM-EDX, it was confirmed that the shape of the aggregate of the melamine polyphosphate particles was an island shape, and a covering rate of the aggregate of the melamine polyphosphate particles was <NUM>%.

<NUM> parts by weight of a graphite powder, <NUM> part by weight of carboxymethyl cellulose (CMC), and <NUM> part by weight of styrene-butadiene rubber (SBR) were mixed, and an appropriate amount of water was further added, thereby preparing a negative electrode mixture slurry. Next, the negative electrode mixture slurry was applied onto both surfaces of a negative electrode current collector formed of a copper foil, and the negative electrode current collector was dried. The negative electrode current collector was cut into a predetermined electrode size and was rolled using a roller to form a negative electrode active material layer on the both surfaces of the negative electrode current collector.

Lithium hexafluorophosphate (LiPF<NUM>) was dissolved in a mixed solvent obtained by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) at a volume ratio of <NUM> : <NUM> : <NUM> so that a concentration thereof was <NUM> mol/liter to prepare a non-aqueous electrolyte.

A non-aqueous electrolyte secondary battery was produced in the same manner as in Example <NUM>, except that the amount of the melamine polyphosphate particles added was <NUM> parts by weight and <NUM> of the prepared filler slurry was applied onto the positive electrode active material layer at a Wet film thickness equivalent to <NUM> in the preparation of the filler slurry. When a surface of the positive electrode of Example <NUM> was observed by SEM-EDX, it was confirmed that the shape of the aggregate of the melamine polyphosphate particles was an island shape, and a covering rate of the aggregate of the melamine polyphosphate particles was <NUM>%.

Non-aqueous electrolyte secondary batteries of Examples <NUM>, <NUM>, and <NUM> were produced in the same manners as in Examples <NUM>, <NUM>, and <NUM>, respectively, except that the melamine polyphosphate particles were replaced with ammonium polyphosphate particles in the preparation of the filler slurry. When surfaces of the positive electrodes of Examples <NUM> to <NUM> were observed by SEM-EDX, it was confirmed that the shape of each of the aggregates of the ammonium polyphosphate particles was an island shape, and covering rates of the aggregates of the ammonium polyphosphate particles were <NUM>%, <NUM>%, and <NUM>%, respectively.

Non-aqueous electrolyte secondary batteries of Examples <NUM>, <NUM>, and <NUM> were produced in the same manners as in Examples <NUM>, <NUM>, and <NUM>, respectively, except that the melamine polyphosphate particles were replaced with lithium metaphosphate ((LiPO<NUM>)n) particles in the preparation of the filler slurry. When surfaces of the positive electrodes of Examples <NUM> to <NUM> were observed by SEM-EDX, it was confirmed that the shape of each of the aggregates of the lithium metaphosphate particles was an island shape, and covering rates of the aggregates of the lithium metaphosphate particles were <NUM>%, <NUM>%, and <NUM>%, respectively.

Non-aqueous electrolyte secondary batteries of Examples <NUM>, <NUM>, and <NUM> were produced in the same manners as in Examples <NUM>, <NUM>, and <NUM>, respectively, except that the melamine polyphosphate particles were replaced with sodium silicate (Na<NUM>SiO<NUM>) particles in the preparation of the filler slurry. When surfaces of the positive electrodes of Examples <NUM> to <NUM> were observed by SEM-EDX, it was confirmed that the shape of each of the aggregates of the sodium silicate particles was an island shape, and covering rates of the aggregates of the sodium silicate particles were <NUM>%, <NUM>%, and <NUM>%, respectively.

Non-aqueous electrolyte secondary batteries of Examples <NUM>, <NUM>, and <NUM> were produced in the same manners as in Examples <NUM>, <NUM>, and <NUM>, respectively, except that the melamine polyphosphate particles were replaced with sodium borate (Na<NUM>B<NUM>O<NUM>) particles in the preparation of the filler slurry. When surfaces of the positive electrodes of Examples <NUM> to <NUM> were observed by SEM-EDX, it was confirmed that the shape of each of the aggregates of the sodium borate particles was an island shape, and covering rates of the aggregates of the sodium borate particles were <NUM>%, <NUM>%, and <NUM>%, respectively.

A non-aqueous electrolyte secondary battery was produced in the same manner as in Example <NUM>, except that the filler slurry was not used.

A non-aqueous electrolyte secondary battery was produced in the same manner as in Example <NUM>, except that the amount of the melamine polyphosphate particles added was <NUM> parts by weight and <NUM> of the prepared filler slurry was applied onto the positive electrode active material layer at a Wet film thickness equivalent to <NUM> in the preparation of the filler slurry.

Non-aqueous electrolyte secondary batteries were produced in the same manner as in Comparative Example <NUM>, except that the melamine polyphosphate particles were replaced with ammonium polyphosphate particles in Comparative Example <NUM>, lithium metaphosphate particles in Comparative Example <NUM>, sodium silicate particles in Comparative Example <NUM>, and sodium borate particles in Comparative Example <NUM> in the preparation of the filler slurry.

When surfaces of the positive electrodes of Comparative Examples <NUM> to <NUM> were observed by SEM-EDX, the island-shaped aggregates of the filler particles ware not confirmed, and covering rates of the aggregates of the filler particles were <NUM>%.

The non-aqueous electrolyte secondary batteries of Examples <NUM> to <NUM> and Comparative Examples <NUM> to <NUM> were subjected to a nail penetration test in the following procedure.

The battery resistance of each of the non-aqueous electrolyte secondary batteries of Examples <NUM> to <NUM> and Comparative Examples <NUM> to <NUM> was measured as follows. Under a temperature environment of <NUM>, the non-aqueous electrolyte secondary battery was charged at a constant current of <NUM> C until the battery voltage reached <NUM> V, the non-aqueous electrolyte secondary battery was charged at a constant voltage until the current value reached <NUM> C, and then, the non-aqueous electrolyte secondary battery was discharged at a constant current of <NUM> C to set SOC to <NUM>%. Next, voltage values when discharge currents of <NUM> A, <NUM> A, <NUM> A, and <NUM> A were applied for <NUM> seconds were acquired. DC-IR was calculated from an absolute value of a slope when the voltage value after <NUM> seconds to each discharge current value was linearly approximated by a least-square method, and the value was summarized in Table <NUM> as the battery resistance.

As shown in Table <NUM>, in all of Examples <NUM> to <NUM> in which the aggregate of the filler particles was present in an island shape on the surface of the positive electrode active material layer, the battery temperature after the nail penetration test was lower than that in Comparative Example <NUM> in which the filler particles were absent on the surface of the positive electrode active material layer. Here, when the covering rate of the aggregate of the filler particles was <NUM>% as in Comparative Examples <NUM> to <NUM>, the battery resistance was significantly increased in comparison to Comparative Example <NUM>. However, in Examples <NUM> to <NUM>, an increase in battery resistance was suppressed in comparison to Comparative Examples <NUM> to <NUM>. That is, in Examples <NUM> to <NUM>, an increase in battery resistance was suppressed, and heat generation of the battery in the nail penetration test was suppressed.

Non-aqueous electrolyte secondary batteries of Examples <NUM> to <NUM> were produced in the same manners as in Examples <NUM> to <NUM>, respectively, except that the filler slurry was applied onto the negative electrode active material layer instead of being applied onto the positive electrode active material layer.

Non-aqueous electrolyte secondary batteries of Comparative Examples <NUM> to <NUM> were produced in the same manners as in Comparative Examples <NUM> to <NUM>, respectively, except that the filler slurry was applied onto the negative electrode active material layer instead of being applied onto the positive electrode active material layer.

The covering rates of the aggregates of the filler particles in Examples <NUM> to <NUM> and Comparative Examples <NUM> to <NUM> are summarized in Table <NUM>. In addition, in the non-aqueous electrolyte secondary batteries of Examples <NUM> to <NUM> and Comparative Examples <NUM> to <NUM>, the nail penetration test and the battery resistance measurement were performed. The results thereof are summarized in Table <NUM>.

As can be seen from Table <NUM>, the results of the negative electrode were similar to those of the positive electrode. That is, in Examples <NUM> to <NUM>, an increase in battery resistance was suppressed, and heat generation of the battery in the nail penetration test was suppressed.

Non-aqueous electrolyte secondary batteries were produced in the same manner as in Example <NUM>, except that the melamine polyphosphate particles were replaced with sodium tripolyphosphate particles in Example <NUM>, potassium phosphate (KH<NUM>PO<NUM>) particles in Example <NUM>, melamine cyanurate in Example <NUM>, potassium pyrosulfate (K<NUM>S<NUM>O<NUM>) particles in Example <NUM>, boron oxide (B<NUM>O<NUM>) particles in Example <NUM>, ethylene-<NUM>,<NUM>-bis(pentabromophenyl) particles in Example <NUM>, ethylenebistetrabromophthalimide particles in Example <NUM>, potassium citrate (C<NUM>H<NUM>K<NUM>O<NUM>) particles in Example <NUM>, potassium carbonate (K<NUM>CO<NUM>) particles in Example <NUM>, and sodium carbonate (Na<NUM>CO<NUM>) particles in Example <NUM> in the preparation of the filler slurry.

The covering rates of the aggregates of the filler particles in Examples <NUM> to <NUM> are summarized in Table <NUM>. In addition, in the non-aqueous electrolyte secondary batteries of Examples <NUM> to <NUM>, the nail penetration test and the battery resistance measurement were performed. The results thereof are summarized in Table <NUM>.

Claim 1:
An electrode (<NUM>) for a non-aqueous electrolyte secondary battery (<NUM>) comprising:
a current collector (<NUM>); an active material layer (<NUM>) that is formed on the current collector (<NUM>); an aggregate (<NUM>) of filler particles that is present in an island shape on a surface of the active material layer (<NUM>),
wherein the filler particles are compound particles containing at least one of phosphorus, silicon, boron, nitrogen, potassium, sodium, and bromine, and a transformation point of the filler particle at which the filler particle is transformed from a solid phase into a liquid phase or is thermally decomposed is in a range of <NUM> to <NUM>,<NUM>.