JP6380269B2 - Method for producing lithium ion secondary battery - Google Patents

Description

The present invention relates to a method for manufacturing a lithium ion secondary battery including a positive electrode plate having a positive electrode active material layer containing positive electrode active material particles, a negative electrode plate, and a non-aqueous electrolyte solution containing a compound containing fluorine.

  Conventionally, in a lithium ion secondary battery (hereinafter also simply referred to as a battery), the positive electrode potential is high, so that the nonaqueous solvent of the nonaqueous electrolyte solution is likely to be oxidatively decomposed on the surface of the positive electrode active material particles. Are known. When hydrogen ions are generated by oxidative decomposition of the non-aqueous solvent, hydrogen ions may react with fluorine to generate hydrofluoric acid (HF) when the non-aqueous electrolyte has a compound containing fluorine. Then, by the action of this hydrofluoric acid, the transition metal in the positive electrode active material particles is eluted, and the battery capacity is reduced. For this reason, in such a battery, there is a problem that the battery capacity is greatly reduced when a charge / discharge cycle test is performed.

In order to solve this problem, a technique in which metal phosphate particles (powder) such as lithium phosphate are included in the positive electrode active material layer is known. When the metal phosphate particles are included in the positive electrode active material layer, when the battery is charged for the first time, the above-described hydrofluoric acid reacts with the metal phosphate, so that fluorine and phosphorus are present on the surface of the positive electrode active material particles. Is formed. Since this coating prevents the non-aqueous electrolyte from coming into direct contact with the positive electrode active material, the non-aqueous solvent can be prevented from being oxidatively decomposed even when the positive electrode potential exceeds the oxidative decomposition potential of the non-aqueous solvent. Therefore, it is possible to suppress a decrease in battery capacity after performing a charge / discharge cycle test on the battery.
For example, Patent Document 1 discloses a technique in which a positive electrode mixture layer (positive electrode active material layer) contains metal phosphate particles such as lithium phosphate and sodium phosphate.

JP 2014-103098 A

However, since the film containing fluorine and phosphorus is itself a resistor, the battery resistance tends to increase when the film is thick. On the other hand, it has been found that when the dispersibility of the metal phosphate particles in the positive electrode active material layer is improved, the battery resistance can be prevented from increasing due to the presence of the coating. The reason is that the better the dispersibility of the metal phosphate particles, the higher the frequency of reaction with hydrofluoric acid, and the reaction for forming the film is completed in a short time, so that the film is formed thinner. For this reason, it is thought that the resistance of the film is lowered and the battery resistance is lowered.
However, in order to reduce the size of metal phosphate particles (nanoparticles) in order to improve the dispersibility of metal phosphate particles, (1) a separate process for reducing the diameter of metal phosphate is added. (2) The metal phosphate particles having a reduced diameter increase the production cost of the battery because of the difficulty in weighing and charging during the production of the paste for the positive electrode active material layer.

The present invention has been made in view of the current situation, and has a lithium ion secondary battery that can produce an inexpensive lithium ion secondary battery while having a coating film containing fluorine and phosphorus on the surface of the positive electrode active material particles. It aims at providing the manufacturing method of a battery .

  One embodiment of the present invention for solving the above problems is a lithium ion including a positive electrode plate having a positive electrode active material layer containing positive electrode active material particles, a negative electrode plate, and a non-aqueous electrolyte solution containing a compound containing fluorine. In the secondary battery, the positive electrode active material particles have a coating film containing fluorine and phosphorus on the particle surface, and the non-aqueous electrolyte is lithium containing at least one of phosphate ions and pyrophosphate ions. It is an ion secondary battery.

According to this lithium ion secondary battery, the nonaqueous electrolytic solution has at least one of phosphate ions (PO ₄ ³⁻ ) and pyrophosphate ions (P ₂ O ₇ ⁴⁻ ). Since phosphate ions or pyrophosphate ions are present in the non-aqueous electrolyte, when the battery is charged for the first time during the battery manufacturing process, the generated hydrofluoric acid is converted to phosphate ions or pyrophosphate in the non-aqueous electrolyte. By reacting with acid ions, a film containing fluorine and phosphorus is formed on the surface of the positive electrode active material particles. As described above, this coating prevents the nonaqueous electrolyte from coming into direct contact with the positive electrode active material, so that the nonaqueous solvent is oxidized even when the positive electrode potential is higher than the oxidative decomposition potential of the nonaqueous solvent. It can suppress being decomposed. Therefore, it is possible to suppress a decrease in battery capacity when a charge / discharge cycle test is performed on the battery.
Moreover, a non-aqueous electrolyte having phosphate ions or pyrophosphate ions can be easily and uniformly produced by dissolving metal phosphate or metal pyrophosphate particles in the non-aqueous electrolyte, and an inexpensive battery is obtained. be able to.

Note that the nonaqueous electrolytic solution having phosphate ions or pyrophosphate ions can be prepared by dissolving metal phosphate or metal pyrophosphate particles in the nonaqueous electrolytic solution as described above.
Examples of the metal phosphate include an alkali metal phosphate represented by M ₃ PO ₄ (M: alkali metal) and M ₃ (PO ₄ ) ₂ (M: Group 2 element). Examples include phosphates of Group 2 elements, or phosphates containing both alkali metals and Group 2 metals.
Furthermore, as the alkali metal phosphate, for example, lithium phosphate (Li ₃ PO ₄ ), sodium phosphate (Na ₃ PO ₄ ), potassium phosphate (K ₃ PO ₄ ), sodium dilithium phosphate (Li ₂ NaPO ₄ ).

Examples of Group 2 element phosphates include magnesium phosphate (Mg ₃ (PO ₄ ) ₂ ) and calcium phosphate (Ca ₃ (PO ₄ ) ₂ ).
Examples of the phosphate containing both alkali metal and Group 2 metal include sodium magnesium phosphate (MgNaPO ₄ ).
In addition, as a metal phosphate, for example, a metal containing an element other than an alkali metal and a Group 2 element such as lithium aluminum germanium phosphate (LAGP: Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ) ₃ ) Also included are phosphates.

Examples of the metal pyrophosphate include an alkali metal pyrophosphate represented by M ₄ P ₂ O ₇ (M: alkali metal) and M ₂ P ₂ O ₇ (M: group 2 element). Group 2 element pyrophosphates.
Further, examples of the alkali metal pyrophosphate include lithium pyrophosphate (Li ₄ P ₂ O ₇ ), sodium pyrophosphate (Na ₄ P ₂ O ₇ ), and potassium pyrophosphate (K ₄ P ₂ O ₇ ). .
Examples of Group 2 element pyrophosphates include magnesium pyrophosphate (Mg ₂ P ₂ O ₇ ) and calcium pyrophosphate (Ca ₂ P ₂ O ₇ ).

Examples of the positive electrode active material forming the “positive electrode active material particles” include lithium transition metal composite oxides. Examples of the lithium transition metal composite oxide include lithium nickel cobalt manganese based composite oxide containing nickel (Ni), cobalt (Co) and manganese (Mn) as transition metals, and nickel and manganese as transition metals. Examples thereof include lithium nickel manganese composite oxide, lithium nickelate (LiNiO ₂ ), lithium cobaltate (LiCoO ₂ ), and lithium manganate (LiMn ₂ O ₄ ).

More specifically, a lithium nickel manganese composite oxide having a spinel crystal structure represented by the following general formula (1) can be used as the positive electrode active material.
_{Li (Ni x M y Mn 2} -xy) O 4 ··· (1)
However, x is x> 0, preferably 0.2 ≦ x ≦ 1.0.
Further, y is y ≧ 0, preferably 0 ≦ y <1.0.
Further, x + y <2.0.
“M” is any transition metal element other than Ni and Mn (eg, one or more selected from Fe, Co, Cu, Cr), or a typical metal element (eg, Zn, Al). 1 type or 2 types or more selected).
Note that whether or not the crystal structure of the positive electrode active material has a spinel structure can be determined by, for example, X-ray structure analysis (preferably single crystal X-ray structure analysis). Specifically, it can be determined by X-ray diffraction measurement using CuKα rays.

The “coating containing fluorine and phosphorus” may contain decomposition products of non-aqueous electrolyte components (electrolytes, non-aqueous solvents, additives, etc.) in addition to fluorine and phosphorus.
In the “positive electrode active material layer”, in addition to the positive electrode active material particles, for example, conductive materials such as graphite, carbon black, and acetylene black, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), styrene butadiene rubber ( A binder such as SBR) can be included.
Examples of the “negative electrode plate” include a negative electrode active material layer including negative electrode active material particles provided on a negative electrode current collector foil. Examples of the negative electrode active material particles include particles made of a carbon material capable of inserting and removing lithium such as graphite.

Examples of the non-aqueous solvent for the “non-aqueous electrolyte solution” include organic solvents such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, and the like. It can be used alone or in admixture of two or more.
As the electrolyte of the "non-aqueous _{electrolyte", LiPF 6, LiBF 4, LiAsF} 6, LiSbF 6, LiCF 3 such SO ₃ and the like, may be used in combination either singly or in combination.

In addition, the “nonaqueous electrolytic solution” may contain an additive other than the above electrolyte. Examples of the additive include fluoride and lithium bisoxalate borate (LiBOB). The fluoride, for _{example, AgF, CoF 2, CoF 3} , CuF, CuF 2, FeF 2, FeF 3, LiF, etc. _{MnF 2, MnF 3, SnF 2} , SnF 4, TiF 3, TiF 4, ZrF 4 is These may be used alone or in combination of two or more.
The “compound containing fluorine” contained in the nonaqueous electrolytic solution may be an electrolyte containing fluorine such as LiPF ₆ or an additive containing fluorine such as LiF. Moreover, the compound containing a fluorine may be only 1 type, and 2 or more types may be contained.

  Furthermore, in the above lithium ion secondary battery, the positive electrode active material layer is preferably a lithium ion secondary battery including particles of at least one of metal phosphate and metal pyrophosphate.

  In this lithium ion secondary battery, not only the phosphate ion and pyrophosphate ion are included in the non-aqueous electrolyte solution, but also the positive electrode active material layer has particles of at least one of metal phosphate and metal pyrophosphate. including. As a result, even when hydrofluoric acid is generated along with the oxidative decomposition of the nonaqueous solvent during use of the battery after production, this hydrofluoric acid is used in addition to phosphate ions and pyrophosphate ions in the nonaqueous electrolyte solution. It can also be consumed by reacting with metal phosphate and metal pyrophosphate particles in the positive electrode active material layer. For this reason, it can suppress that the transition metal in a positive electrode active material particle elutes by the effect | action of a hydrofluoric acid, and battery capacity decreases. Therefore, it is possible to more effectively suppress the battery capacity from decreasing when the charge / discharge cycle test is performed.

  The metal phosphate and metal pyrophosphate particles included in the positive electrode active material layer have the same composition as the metal phosphate and metal pyrophosphate particles dissolved in the non-aqueous electrolyte (for example, both lithium phosphate Particles) or a different composition (for example, lithium phosphate particles are dissolved in a non-aqueous electrolyte and sodium phosphate particles are included in the positive electrode active material layer).

Furthermore, in any of the above lithium ion secondary batteries, the redox potential of the positive electrode active material particles (SOC 0% to 100%) in any of the operating ranges (SOC 0% to 100%) of the lithium ion secondary battery. It is preferable to use a lithium ion secondary battery having an operating potential) of 4.3 V (vs. Li / Li ⁺ ) or higher.

In this lithium ion secondary battery, since the redox potential of the positive electrode active material particles is a high potential of 4.3 V (vs. Li ^/ Li ⁺ ) or higher in any SOC within SOC 0% to 100%, The nonaqueous solvent of the nonaqueous electrolytic solution is easily oxidized and decomposed on the surface of the active material particles, and hydrofluoric acid is easily generated. However, as described above, since the coating film containing fluorine and phosphorus is formed on the surface of the positive electrode active material particles, the oxidative decomposition of the non-aqueous solvent is prevented, and the positive electrode active material particles in the positive electrode active material particles are activated by the action of hydrofluoric acid. It is possible to more effectively suppress the decrease of the battery capacity by preventing elution of the transition metal.

Moreover, as another aspect, the positive electrode plate having a positive electrode active material layer containing positive electrode active material particles, a negative electrode plate, and a non-aqueous electrolyte solution containing a compound containing fluorine, the positive electrode active material particles include: on the particle surface has a coating containing fluorine and phosphorus, the non-aqueous electrolyte, saw including at least one of phosphate ion and pyrophosphate ions, the positive electrode active material layer, metal phosphates and metal A method for manufacturing a lithium ion secondary battery including at least one particle of pyrophosphate, an assembling process for assembling a battery using the positive electrode plate, the negative electrode plate, and the non-aqueous electrolyte, and the assembling process after, and initial charge of the battery, Rutotomoni the generated hydrogen fluoride is reacted with phosphoric acid ions and pyrophosphate ions in the nonaqueous electrolyte solution, and the metal phosphate particles of the positive electrode active material layer Metal pyrroline Is reacted with a salt particles, the positive electrode active material film formation step of forming the coating on the particle surfaces of the particles, comprising a non-aqueous electrolyte solution used in the assembly process, pre phosphate ion and pyrophosphate ion It is preferable to use a method for producing a lithium ion secondary battery that is an electrolytic solution containing at least one of the above .

In this method of manufacturing a lithium ion secondary battery, after the battery is assembled, the battery is initially charged, and the generated hydrofluoric acid is reacted with phosphate ions and pyrophosphate ions in the non-aqueous electrolyte solution. By reacting with metal phosphate particles and metal pyrophosphate particles in the material layer, a film containing fluorine and phosphorus is formed on the particle surface of the positive electrode active material particles. By doing in this way, a uniform film can be easily formed on the particle surface of positive electrode active material particles, and a battery can be manufactured at low cost.

1 is a perspective view of a lithium ion secondary battery according to an embodiment. It is the longitudinal cross-sectional view which cut | disconnected the lithium ion secondary battery which concerns on embodiment by the plane in alignment with a battery horizontal direction and a battery vertical direction. It is an expanded view of an electrode body which concerns on embodiment and shows the state which mutually accumulated the positive electrode plate and the negative electrode plate through the separator. It is explanatory drawing which shows typically the mode of particle surface vicinity among the cross sections of positive electrode active material particle in connection with embodiment. It is a graph which shows the relationship between the addition amount to the non-aqueous electrolyte of metal phosphate particle | grains, and the capacity | capacitance maintenance factor of a battery about each battery which concerns on an Example and a comparative example. It is a graph which shows the relationship between the addition amount to the non-aqueous electrolyte of a metal phosphate particle, and battery resistance ratio about each battery which concerns on an Example and a comparative example.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. 1 and 2 show a lithium ion secondary battery (hereinafter also simply referred to as “battery”) 1 according to the present embodiment. FIG. 3 shows a development view of the electrode body 20 constituting the battery 1. In the following description, the battery thickness direction BH, the battery lateral direction CH, and the battery vertical direction DH of the battery 1 are defined as the directions shown in FIGS. 1 and 2.
The battery 1 is a rectangular and sealed lithium ion secondary battery mounted on a vehicle such as a hybrid vehicle or an electric vehicle. The battery 1 includes a battery case 10, an electrode body 20 and a nonaqueous electrolyte solution 40 accommodated therein, a positive terminal 50 and a negative terminal 51 supported by the battery case 10, and the like.

  Among these, the battery case 10 has a rectangular parallelepiped shape and is made of metal (in this embodiment, aluminum). This battery case 10 includes a rectangular parallelepiped box-shaped case main body member 11 whose upper side is opened, and a rectangular plate-shaped case lid member 13 welded in a form to close the opening 11h of the case main body member 11. . The case lid member 13 is provided with a safety valve 14 that opens when the internal pressure of the battery case 10 reaches a predetermined pressure. The case lid member 13 is formed with a liquid injection hole 13 h that communicates the inside and outside of the battery case 10 and is hermetically sealed with a sealing member 15.

  Further, the case lid member 13 has a positive terminal 50 and a negative terminal 51 formed of an internal terminal member 53, an external terminal member 54, and a bolt 55, respectively, via an internal insulating member 57 and an external insulating member 58 made of resin. It is fixed. The positive terminal 50 is made of aluminum, and the negative terminal 51 is made of copper. In the battery case 10, the positive electrode terminal 50 is connected and connected to the positive electrode current collector 21 m of the positive electrode plate 21 in the electrode body 20 described later. Further, the negative electrode terminal 51 is connected to the negative electrode current collector 31 m of the negative electrode plate 31 in the electrode body 20 and is conductive.

  Next, the electrode body 20 will be described (see FIGS. 2 and 3). The electrode body 20 has a flat shape and is accommodated in the battery case 10. The electrode body 20 is obtained by winding a belt-like positive electrode plate 21 and a belt-like negative electrode plate 31 on each other via a pair of belt-like separators 39 and compressing them in a flat shape.

The positive electrode plate 21 is formed by providing a positive electrode active material layer 23 in a band shape on a region extending in a part of the width direction and extending in the longitudinal direction among both main surfaces of a positive electrode current collector foil 22 made of a band-shaped aluminum foil. The positive electrode active material layer 23 includes positive electrode active material particles 24, a conductive material (conductive aid) 26, a binder 27, and metal phosphate particles 28, which will be described later. In the present embodiment, acetylene black (AB) is used as the conductive material 26, polyvinylidene fluoride (PVDF) is used as the binder 27, and lithium phosphate (Li ₃ PO ₄ ) particles (powder) are used as the metal phosphate particles 28. Used.

The mixing ratio of the positive electrode active material particles 24, the conductive material 26, and the binder 27 is 89: 8: 3 by weight. In addition, the compounding ratio of the metal phosphate (lithium phosphate) particles 28 is 2.95 parts by weight based on the positive electrode active material particles 24 (100 parts by weight).
One end of the positive electrode current collector foil 22 in the width direction is a positive electrode current collector part 21 m in which the positive electrode current collector foil 22 is exposed without the positive electrode active material layer 23 in the thickness direction of the positive electrode current collector foil 22. The positive electrode terminal 50 described above is welded to the positive electrode current collector 21m.

In the present embodiment, the positive electrode active material particles 24 are made of lithium transition metal composite oxide, specifically, LiNi _0.5 Mn _1.5 O ₄ which is one of lithium nickel manganese composite oxide having a spinel crystal structure. Particles. A coating 25 containing fluorine and phosphorus is formed on the particle surface 24n of the positive electrode active material particles 24 (see FIG. 4). In addition to fluorine and phosphorus, the coating 25 includes decomposition products of other components (electrolyte and nonaqueous solvent) of the nonaqueous electrolytic solution 40.

Next, the negative electrode plate 31 will be described. This negative electrode plate 31 is provided with a negative electrode active material layer 33 in a band shape on a region extending in a part of the width direction and extending in the longitudinal direction out of both main surfaces of a negative electrode current collector foil 32 made of a strip-shaped copper foil. . The negative electrode active material layer 33 includes negative electrode active material particles, a binder, and a thickener. In the present embodiment, graphite particles are used as negative electrode active material particles, styrene butadiene rubber (SBR) is used as a binder, and carboxymethyl cellulose (CMC) is used as a thickener. Also, one end in the width direction of the negative electrode current collector foil 32 is the negative electrode current collector part 31m where the negative electrode active material layer 33 is not present in the thickness direction of the negative electrode current collector foil 32 and the negative electrode current collector foil 32 is exposed. Yes. The negative electrode terminal 51 described above is welded to the negative electrode current collector 31m.
The separator 39 is a porous film made of resin and has a strip shape.

Next, the nonaqueous electrolytic solution 40 will be described. The non-aqueous electrolyte 40 is accommodated in the battery case 10, a part of the non-aqueous electrolyte 40 is impregnated in the electrode body 20, and the rest is accumulated at the bottom of the battery case 10 as an excess liquid. The electrolyte of this nonaqueous electrolytic solution 40 is lithium hexafluorophosphate (LiPF ₆ ), and its concentration is 1.0M. The nonaqueous solvent of the nonaqueous electrolytic solution 40 is a mixed organic solvent in which fluoroethylene carbonate (FEC) and 2,2,2-trifluoroethyl methyl carbonate are mixed at a volume ratio of 1: 1. As described above, the nonaqueous electrolytic solution 40 has LiPF ₆ as the compound 41 containing fluorine.
Further, as will be described later, the metal phosphate particles 42, specifically, lithium phosphate (Li ₃ PO ₄ ) particles are dissolved in the non-aqueous electrolyte 40. Contains phosphate ions (PO ₄ ³⁻ ).

Next, a method for manufacturing the battery 1 will be described. First, the positive electrode plate 21 is formed. Specifically, positive electrode active material particles 24 made of LiNi _0.5 Mn _1.5 O ₄ which is a lithium nickel manganese composite oxide having a spinel structure are prepared. The positive electrode active material particles 24, the conductive material 26 (acetylene black), the binder 27 (polyvinylidene fluoride), the metal phosphate particles 28 (lithium phosphate particles, center particle size 1.5 μm), Is kneaded with a solvent (NMP in this embodiment) to produce a positive electrode paste.

The mixing ratio of the positive electrode active material particles 24, the conductive material 26, and the binder 27 is 89: 8: 3 by weight. In addition, the compounding ratio of the metal phosphate (lithium phosphate) particles 28 is 2.95 parts by weight based on the positive electrode active material particles 24 (100 parts by weight).
Thereafter, this positive electrode paste is applied to one main surface of the positive electrode current collector foil 22 made of a strip-shaped aluminum foil and dried to form the positive electrode active material layer 23. Further, a positive electrode paste is applied to the other main surface of the positive electrode current collector foil 22 and dried to form the positive electrode active material layer 23. Then, this is pressed and the positive electrode plate 21 is obtained.
Separately, the negative electrode plate 31 is formed by a known method.

Next, the positive electrode plate 21 and the negative electrode plate 31 are overlapped with each other via a pair of separators 39 and wound using a winding core. Further, the electrode body 20 is formed by compressing it into a flat shape.
Separately, a case lid member 13, an internal terminal member 53, an external terminal member 54, a bolt 55, an internal insulating member 57 and an external insulating member 58 are prepared. Then, the positive terminal 50 and the negative terminal 51 including the internal terminal member 53, the external terminal member 54, and the bolt 55 are fixed to the case lid member 13 via the internal insulating member 57 and the external insulating member 58, respectively. Thereafter, the positive electrode terminal 50 and the negative electrode terminal 51 integrated with the case lid member 13 are welded to the positive electrode current collector 21m and the negative electrode current collector 31m of the electrode body 20, respectively.
Next, the case body member 11 is prepared, and after the electrode body 20 is accommodated in the case body member 11, the case lid member 13 is welded to the case body member 11 to form the battery case 10.

Separately, a non-aqueous electrolyte 40 is prepared. Specifically, LiPF ₆ (compound 41 containing fluorine) is added at a concentration of 1.0M to a mixed organic solvent in which fluoroethylene carbonate and 2,2,2-trifluoroethyl methyl carbonate are mixed at a volume ratio of 1: 1. Dissolve so that Further, metal phosphate (lithium phosphate) particles 42 are dissolved in this. Specifically, when the weight of the positive electrode active material particles 24 contained in the positive electrode active material layer 23 accommodated in the battery 1 is used as a reference (100 parts by weight), the nonaqueous electrolytic solution injected into the battery 1 The metal phosphate particles 42 are dissolved in the above-described electrolytic solution so that the metal phosphate particles 42 dissolved in 40 are 0.05 parts by weight. Thereby, the nonaqueous electrolyte solution 40 containing a phosphate ion is obtained.
Then, the nonaqueous electrolytic solution 40 is injected into the battery case 10 through the injection hole 13h, and the electrode body 20 is impregnated with the nonaqueous electrolytic solution 40. Thereafter, the liquid injection hole 13h is temporarily sealed.

Next, the battery is initially charged to form a coating 25 containing fluorine and phosphorus on the particle surface 24 n of the positive electrode active material particles 24. Specifically, this battery is charged to a battery voltage of 4.9 V with a constant current of 5 C (CC-CV charging).
At the time of this initial charge, on the particle surface 24n of the positive electrode active material particles 24, the nonaqueous solvent of the nonaqueous electrolytic solution 40 is oxidized and decomposed to generate hydrogen ions. This hydrogen ion reacts with the fluorine-containing compound 41 (LiPF _{6 in the} present embodiment) in the nonaqueous electrolytic solution 40 to generate hydrofluoric acid (HF). First, the hydrofluoric acid preferentially reacts with phosphate ions in the non-aqueous electrolyte solution 40 to form a coating film 25 containing fluorine and phosphorus on the particle surface 24 n of the positive electrode active material particles 24. Thereafter, when phosphate ions in the non-aqueous electrolyte solution 40 present in the vicinity of the positive electrode active material particles 24 are reduced, metal phosphate (lithium phosphate) particles 28 contained in the positive electrode active material layer 23 are generated. By reacting with an acid, a film 25 containing fluorine and phosphorus is further formed.
Thereafter, various inspections are performed on the battery. Thus, the battery 1 is completed.

(Examples and Comparative Examples)
Subsequently, the result of the test conducted in order to verify the effect of this invention is demonstrated. As shown in Table 1 below, five types of batteries of Examples 1 to 3 and Comparative Examples 1 and 2 were prepared. Specifically, in each of the batteries of Examples 1 to 3 and Comparative Example 2, in order to unify the conditions, the weight of the positive electrode active material particles contained in the positive electrode active material layer accommodated in each battery was determined based on the weight (100 wt. Part), the total amount of metal phosphate (lithium phosphate) particles contained in each battery was 3.00 parts by weight in any battery.

  In the battery of Comparative Example 2, 3.00 parts by weight of metal phosphate particles were added only to the positive electrode active material layer. Therefore, the battery of Comparative Example 2 does not have phosphate ions in the nonaqueous electrolytic solution. On the other hand, in the battery of Example 1, 2.98 parts by weight of metal phosphate particles were added to the positive electrode active material layer, and the remaining 0.02 parts by weight of metal phosphate particles were added to the non-aqueous electrolyte. (Dissolved). In the battery of Example 2, 2.95 parts by weight of metal phosphate particles were added to the positive electrode active material layer, and the remaining 0.05 parts by weight of metal phosphate particles were added to the non-aqueous electrolyte. (Dissolved). In the battery of Example 3, 2.90 parts by weight of metal phosphate particles were added to the positive electrode active material layer, and the remaining 0.10 parts by weight of metal phosphate particles were added to the non-aqueous electrolyte. (Dissolved). In addition, the battery of the comparative example 1 does not contain a metal phosphate in the battery. That is, the battery of Comparative Example 1 does not include metal phosphate particles in the positive electrode active material layer, and does not have phosphate ions in the nonaqueous electrolytic solution. The battery of Example 2 is the same as the battery 1 of the above-described embodiment. Moreover, about each battery of Examples 1 and 3 and Comparative Examples 1 and 2, parts other than the above were the same as those of the battery 1 of the embodiment.

  Next, for each of the batteries of Examples 1 to 3 and Comparative Examples 1 and 2, a “charge / discharge cycle test” was performed, and the capacity retention ratio (%) before and after the test was obtained. Specifically, in a temperature environment of 60 ° C., each battery is charged from 3.5 V to 4.9 V with a constant current of 2 C, and then paused for 10 minutes. Thereafter, the battery is discharged to 3.5 V with a constant current of 2 C, and then rests for 10 minutes. Such charging / discharging was made into 1 cycle, and charging / discharging was performed 100 cycles. The battery capacity was measured before and after the charge / discharge cycle test, and the capacity retention rate (%) was calculated from the battery capacity after the test with respect to the battery capacity before the test. The results are shown in Table 1 and FIG.

As can be seen from Table 1 and FIG. 5, the positive electrode active material layer does not contain metal phosphate particles, and the non-aqueous electrolyte does not have phosphate ions. Each of the batteries of Examples 1 to 3 including metal phosphate particles in the nonaqueous electrolyte solution and phosphate ions in the nonaqueous electrolyte solution, and the positive electrode active material layer includes the metal phosphate particles. It can be seen that all of the batteries of Comparative Example 2 having no phosphate ion have a high capacity retention rate (84.0% or more).
The reason is considered as follows. That is, the battery of Comparative Example 1 does not contain metal phosphate particles in the positive electrode active material layer and does not have phosphate ions in the non-aqueous electrolyte, so when the battery is first charged in the battery manufacturing process. The film containing fluorine and phosphorus is not formed on the surface of the positive electrode active material particles. For this reason, when the positive electrode potential becomes higher than the oxidative decomposition potential of the non-aqueous solvent, the non-aqueous solvent is oxidatively decomposed, hydrogen ions and thus hydrofluoric acid are generated, and the transition metal is eluted from the positive electrode active material particles. For this reason, it is thought that the battery capacity was greatly reduced in the charge / discharge cycle test.

On the other hand, in each of the batteries of Examples 1 to 3, when the battery was charged for the first time, the generated hydrofluoric acid first reacted preferentially with phosphate ions in the non-aqueous electrolyte, and particles of positive electrode active material particles A film containing fluorine and phosphorus is formed on the surface. After that, when the phosphate ions in the non-aqueous electrolyte present in the vicinity of the positive electrode active material particles are reduced, the metal phosphate particles contained in the positive electrode active material layer react with the generated hydrofluoric acid, and fluorine and phosphorus are removed. A coating film is further formed.
In the battery of Comparative Example 2, since the non-aqueous electrolyte does not have phosphate ions, the hydrofluoric acid generated when the battery is charged for the first time reacts with the metal phosphate particles contained in the positive electrode active material layer. Thus, a film containing fluorine and phosphorus is formed on the surface of the positive electrode active material particles.

  In each of the batteries of Examples 1 to 3 and Comparative Example 2, a film having a sufficient thickness is formed on the particle surface of the positive electrode active material particles by the initial charge. For this reason, the non-aqueous electrolyte is prevented from coming into direct contact with the positive electrode active material due to the presence of the coating. Therefore, even when the positive electrode potential is higher than the oxidative decomposition potential of the non-aqueous solvent, the non-aqueous solvent is oxidized and decomposed. In addition, hydrogen ions and, in turn, hydrofluoric acid are generated, and the elution of transition metals from the positive electrode active material particles can be suppressed. For this reason, even when a charge / discharge cycle test is performed on the battery, it is considered that the decrease in battery capacity could be suppressed.

  Next, about each battery of Examples 1-3 and Comparative Examples 1 and 2, battery resistance (IV resistance) was measured, respectively. Specifically, in a temperature environment of 25 ° C., each battery is adjusted to a battery voltage of 3.5 V (SOC 60%), discharged at a constant current of 0.3 C for 10 seconds, and a change in the battery voltage value before and after the discharge. Was measured. Further, only the discharge current value was different from 1C, 3C, and 5C, and discharge was performed under the same conditions as above, and the change in the battery voltage value was measured before and after the discharge for 10 seconds. After that, these data are plotted on a coordinate plane with the horizontal axis representing the discharge current value and the vertical axis representing the change in the battery voltage value before and after the discharge, and an approximate straight line (primary expression) is calculated by the least square method, and the slope Was obtained as an IV resistance value. Then, the “battery resistance ratio” of other batteries was calculated using the battery resistance (IV resistance) of the battery of Comparative Example 2 as a reference (= 1.00). The results are shown in Table 1 and FIG.

  As can be seen from Table 1 and FIG. 6, when phosphate ions are present in the non-aqueous electrolyte (Examples 1 to 3), compared to the case where phosphate ions are not present in the non-aqueous electrolyte (Comparative Example 2). Thus, it can be seen that the battery resistance is lowered. It can also be seen that the battery resistance decreases as the addition amount is increased at least in the range (Examples 1 to 3) where the addition amount (dissolution amount) of the metal phosphate particles to the nonaqueous electrolytic solution is 0.10 wt. .

  The reason is considered as follows. That is, since the metal phosphate particles used in Examples 1 to 3 and Comparative Example 2 have a particle size of 1.5 μm and a large particle size, the dispersibility of the metal phosphate particles in the positive electrode active material layer is high. Not good. Since the battery of Comparative Example 2 does not have phosphate ions in the nonaqueous electrolytic solution, the coating is formed only by the metal phosphate particles in the positive electrode active material layer as described above. This film is considered to have increased battery resistance because it is less uniform and thicker than the film formed by the reaction of phosphate ions and hydrofluoric acid in the non-aqueous electrolyte.

  On the other hand, in each of the batteries of Examples 1 to 3, since the non-aqueous electrolyte has phosphate ions, as described above, the generated hydrofluoric acid is first in the non-aqueous electrolyte as described above. It reacts preferentially with the phosphate ions to form a uniform thin film on the surface of the positive electrode active material particles. When the phosphate ions in the non-aqueous electrolyte present in the vicinity of the positive electrode active material particles are reduced, the metal phosphate particles contained in the positive electrode active material layer react with the generated hydrofluoric acid to further coat the film. Form. As described above, the film formed by reacting with the phosphate ions in the non-aqueous electrolyte is formed uniformly and thinner than the film formed by reacting with the metal phosphate particles in the positive electrode active material layer. Battery resistance is lowered. For this reason, in each battery of Examples 1-3, it is thought that battery resistance became low compared with the battery of the comparative example 2.

  Moreover, when the batteries of Examples 1 to 3 are compared, the amount of phosphate ions contained in the non-aqueous electrolyte is the largest in the battery of Example 3 and the smallest in the battery of Example 1. For this reason, the ratio of the film formed by reacting with phosphate ions in the non-aqueous electrolyte among the films formed at the time of initial charge is the largest in the battery of Example 3 and the smallest in the battery of Example 1 ( In other words, the ratio of the film formed by reacting with the metal phosphate particles contained in the positive electrode active material layer in the film formed at the time of initial charge is the smallest in the battery of Example 3, and Most common with batteries). Accordingly, the battery of Example 2 is made thinner than the battery of Example 1, and the battery of Example 3 is made thinner than the battery of Example 2 more uniformly. For this reason, it is considered that the battery resistance of the battery of Example 2 is lower than that of the battery of Example 1, and the battery of Example 3 is lower than that of the battery of Example 2.

  Incidentally, the battery of Comparative Example 1 has the lowest battery resistance because, in the battery of Comparative Example 1, as described above, a film containing fluorine and phosphorus is formed on the surface of the positive electrode active material particles during the initial charge. Not. Since this film is a resistor, it is considered that the battery of Comparative Example 1 in which the film was not formed has a low battery resistance. However, if a film is not formed on the positive electrode active material particles, the capacity retention rate after the charge / discharge cycle test is greatly reduced as described above, such being undesirable.

As described above, in the battery 1, phosphate ions (PO ₄ ³⁻ ) are present in the non-aqueous electrolyte 40. Therefore, when the battery is initially charged in the manufacturing process of the battery 1, The acid reacts with phosphate ions in the nonaqueous electrolytic solution 40, and a coating 25 containing fluorine and phosphorus is formed on the particle surface 24 n of the positive electrode active material particles 24. The coating 25 suppresses the non-aqueous electrolyte 40 from coming into direct contact with the positive electrode active material, so that the non-aqueous solvent is oxidatively decomposed even when the positive electrode potential is higher than the oxidative decomposition potential of the non-aqueous solvent. Can be suppressed. Therefore, when the battery 1 is subjected to a charge / discharge cycle test, it is possible to suppress a decrease in battery capacity.
Moreover, the non-aqueous electrolyte solution 40 having phosphate ions can be easily manufactured by dissolving the metal phosphate (lithium phosphate) particles 42 in the non-aqueous electrolyte solution 40, and the battery 1 can be made inexpensive. .

In the above, the present invention has been described with reference to the embodiment. However, the present invention is not limited to the above-described embodiment, and it is needless to say that the present invention can be appropriately modified and applied without departing from the gist thereof.
For example, in the embodiment, the lithium phosphate particles are dissolved in the non-aqueous electrolyte to produce the non-aqueous electrolyte 40 containing phosphate ions, but the present invention is not limited to this. For example, other metal phosphate particles such as sodium phosphate, potassium phosphate, magnesium phosphate, and calcium phosphate may be dissolved in the non-aqueous electrolyte to produce a non-aqueous electrolyte containing phosphate ions.
The non-aqueous electrolyte may be an electrolyte containing pyrophosphate ions. Specifically, pyrophosphate particles such as lithium pyrophosphate, sodium pyrophosphate, magnesium pyrophosphate, and calcium pyrophosphate may be dissolved in a non-aqueous electrolyte to produce a non-aqueous electrolyte containing pyrophosphate ions. .

1 Lithium ion secondary battery (battery)
DESCRIPTION OF SYMBOLS 20 Electrode body 21 Positive electrode plate 22 Positive electrode current collection foil 23 Positive electrode active material layer 24 Positive electrode active material particle 24n Particle | grain surface 25 Coating 28 Metal phosphate particle 31 Negative electrode plate 40 Non-aqueous electrolyte 41 Fluorine containing compound 42 Metal phosphate particle

Claims (1)

A positive electrode plate having a positive electrode active material layer containing positive electrode active material particles, a negative electrode plate, and a non-aqueous electrolyte solution containing a compound containing fluorine,
The positive electrode active material particles have a film containing fluorine and phosphorus on the particle surface,
The non-aqueous electrolyte contains at least one of phosphate ions and pyrophosphate ions,
The positive electrode active material layer includes particles of at least one of metal phosphate and metal pyrophosphate.
A method for producing a lithium ion secondary battery, comprising:
An assembly step of assembling a battery using the positive electrode plate, the negative electrode plate and the non-aqueous electrolyte;
After the assembly step, the battery is initially charged, the generated hydrofluoric acid is reacted with phosphate ions and pyrophosphate ions in the non-aqueous electrolyte, and the metal phosphate in the positive electrode active material layer A film forming step of reacting the particles and metal pyrophosphate particles to form the film on the particle surfaces of the positive electrode active material particles,
The non-aqueous electrolyte used in the assembly process is an electrolyte containing at least one of phosphate ions and pyrophosphate ions in advance.
A method for producing a lithium ion secondary battery.

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