Positive electrode active material for a lithium ion secondary battery

Abstract

The present invention provides a positive electrode active material for a lithium ion battery, the positive electrode active material comprising a doped lithium manganese iron phosphate (dLMFP) according to the following molecular formula: LiMn x Fe y M 1‑x‑ y PO4 (where 0.9 < x + y < 1; M is selected from one or more of Mg, Ca, and Ba) and a blend of a lithium nickel cobalt manganese oxide (NMC) compound (the Ni content of which is greater than 0.6 relative to the total amount of metals other than Li) and a lithium nickel cobalt aluminum oxide (NCA) compound. In particular, the present invention provides a blend in which the weight ratio of dLMFP to NMC and / or NCA (i.e., dLMFP:(NMC + NCA)) is >70:<30, such as 75:25, 80:20, 85:15, 90:10, etc.

Description

Technical Field

[0001] The present invention relates to an active material for a positive electrode (or cathode) intended for a rechargeable lithium electrochemical cell (or secondary battery), and also to a lithium-ion secondary battery including a cathode having said positive electrode active material. Background Art

[0002] In a secondary battery, an active material is a material that participates in an electrochemical reaction to generate electric energy when the secondary battery discharges. Transition metal lithiated oxides are considered to be cathode active materials that can be used in lithium secondary batteries. In a positive electrode, the general formula of the lithiated oxide of a transition metal is LiMO2, where M represents at least one transition metal (e.g., Mn, Ni, Co, or a mixture thereof), and it is commonly used as an active material. These active materials allow for high performance, particularly in terms of cyclic reversible capacity (where the reversible capacity represents the stable capacity provided by the electrode after completion of the formation cycle) and lifespan. For example, the capacities of LiCoO2 and LiNiO2 are approximately 180 mAh / g and 220 mAh / g, respectively. However, LiCoO2 has two main drawbacks, namely toxicity and high cost.

[0003] The use of lithiated oxides of manganese is also known, which belong to the spinel family and have the molecular formula LiMn2O4. This compound is low in cost and non-toxic, but it has a reduced capacity (110 mAh / g) and a shortened lifespan due to the significant dissolution of the oxide in the secondary battery electrolyte.

[0004] Another known active cathode material is the compound Li(Ni 0.8 Co 0.15 Al 0.05 )O2, which is the lithiated oxide of nickel cobalt aluminum (or NCA). This material is used as the positive electrode of a lithium rechargeable generator for industrial applications (e.g., electric hybrid vehicles and space applications). However, this type of active material does not have sufficient thermal stability. In fact, in the case of overcharging or accidental short-circuiting of the generator, due to the exothermic reaction of the active material with the electrolyte, the temperature will increase significantly and suddenly. Given the very unstable structure of most materials, overheating can cause the degradation of these active materials. When these positive electrode materials are used in small generators intended to provide strong current (power components), their insufficient thermal stability can cause safety problems.

[0005] Other active materials that are less costly than LiCoO2, exhibit good thermal stability, and are non-toxic have been studied, among which are lithiated phosphates of at least one transition metal, such as LiFePO4 and LiMnPO4. However, the use of LiFePO4 and LiMnPO4 is hindered by their low electronic conductivity. To obtain a secondary battery with good discharge performance at high currents, it is generally necessary to add a high proportion of an electron-conducting material to the electrode. In addition, due to the low electrochemical working potential of LiFePO4, it has a lower specific energy. LiMnPO4 has a higher working potential, but on the other hand, under cycling conditions, when it is used as a positive electrode material in a secondary battery together with a graphite negative electrode, it exhibits poor lifetime. In addition, it is difficult to reduce the porosity of an electrode made of any of these materials, which results in a low unit mass capacity of a battery containing these materials.

[0006] US 2002 / 0004169 (US'169) discloses a lithium-ion battery that is less costly than conventional lithium-ion batteries. US'169 discloses that the operating stability of the lithium-ion battery under special conditions (such as high temperature) is improved and it exhibits excellent over-discharge resistance characteristics, while ensuring compatibility equivalent to the working voltage and energy density of conventional lithium-ion batteries compared to conventional lithium-ion batteries. For this purpose, US'169 discloses a positive electrode active material that is a composite material of a first lithium compound and a second lithium compound (having a potential higher than that of the first lithium compound) represented by the molecular formula Li x M y PO4 (where 0 < x < 2, 0.8 < y < 1.2, and M includes Fe). In US'169, there is no clear definition of the potential mentioned. In US'169, the first lithium compound is used to improve stability and reduce costs. In its examples, US'169 uses LiFePO4 (LFP) as the first lithium compound in combination with LiCoO2, LiMn 0.8 Mg 0.2 O2 or LiNi 0.8 Co 0.2 O2 as the second lithium compound. Other examples use LiFe 0.4 Mn 0.6 PO4 (LFMP) as the first lithium compound and LiMn 0.8 Mg 0.2 O2 as the second lithium compound. In the examples of US'169, the weight ratio of the first lithium compound (LFP or LFMP) to the second lithium compound is from 10:90 to 50:50.

[0007] US 8,828,605 (US'605) discloses a cathode material mixture, which includes: at least one of lithium cobaltate and lithium nickelate; and at least one of a manganese spinel represented by the empirical formula Li (1+x1) (Mn 1-y1 A' y1 ) 2-x1 O z1 (where A' is at least one of Mg, Al, Co, Ni, and Cr) and an olivine compound represented by the formula Li (1-x2) A” x2 MPO4 (where A” is at least one of Na, Mg, Ca, K, Ni, and Nb; M is at least one of Fe, Mn, Co, and Mg). In another embodiment, US'605 discloses an active cathode material mixture, which includes: lithium nickelate selected from LiCoO2-coated LiNi 0.8 Co 0.15 Al 0.05 O2 and Li(Ni 1 / 3 Co 1 / 3 Mn 1 / 3 )O2; and a manganese spinel represented by the empirical formula Li (1+x7) Mn 2-y7 O z7 . In the examples of US'605, there is no embodiment with an LFMP compound as the manganese spinel, and the implemented manganese spinel compound is always a minor component of the active material mixture.

[0008] US 2016 / 0233488 (US'488) discloses a cathode material mixture, which includes (a) at least one compound of the formula Li (1+x) [Ni a Co b Mn c M 1d (1-x) O2 (where x is from 0.01 to 0.05, a is from 0.3 to 0.6, b is from 0 to 0.35, c is from 0.2 to 0.6, d is from 0 to 0.05, a + b + c + d = 1, and M1 is at least one metal selected from Ca, Zn, Fe, Ti, Ba, and Al), (b) a compound of the formula LiFe (1-x) M 2y ​At least one compound of PO4 (where y is from 0 to 0.8 and M2 is selected from Ti, Co, Mn, Ni, V, Mg, Nd, Zn, and Y), which includes at least one additional iron - phosphorus compound in the form of a solid solution in compound (b) or in a domain, and (c) conductively modified carbon. In the examples of US'488, the LFMP compound was not used as a manganate spinel, and the manganate spinel was always a minor component of the active material mixture. In the examples of US'488, there was no embodiment where the LFMP compound was used as a manganate spinel, and the compound of formula (II) was always a minor component of the active material mixture.

[0009] US 2011 / 0223482 (US'482) discloses a positive electrode material mixture that includes lithium manganese iron phosphate (LMFP) and lithium - nickel - manganese - cobalt composite oxide (NMC). In the examples of US'482, the weight ratio of LMFP to NMC is from 10:90 to 70:30. US'482 does not disclose doped LMFP.

[0010] However, there is still a need for a secondary battery for a battery management system (BMS) that has a high capacity per unit mass, a high cycle life, improved rate capacity, and improved ease of use. The present disclosure provides a positive electrode active material that addresses these needs. Summary of the Invention

[0011] Embodiments of the present invention relate to a positive electrode active material that includes a blend of doped lithium iron phosphate (dLMFP) with a lithium nickel cobalt manganese oxide (NMC) compound (i.e., a lithiated oxide of nickel (Ni), manganese (Mn), and cobalt (Co), where the Ni content is greater than 0.6 relative to the total amount of metals other than Li) or a lithium nickel cobalt aluminum oxide (NCA) compound (i.e., a lithiated oxide of Ni, Co, and aluminum (Al)), and this blend can meet the above - mentioned needs. Embodiments of the present invention also relate to a lithium - ion secondary battery that includes this positive electrode active material.

[0012] In an embodiment of the present invention, the positive electrode active material includes a doped lithium manganese iron phosphate (dLFMP) compound according to the following formula (1):

[0013] LiMn x Fe y M 1-x-y PO4 (1),

[0014] wherein, in formula (1):

[0015] 0.9 < x + y < 1; and

[0016] M is selected from one or more of Co, Ni, V, Y, Mg, Ca, Ba, Al, Sc, and Nd.

[0017] In some embodiments, the positive electrode active material includes the lithium nickel cobalt manganese oxide (NMC) compound and the lithium nickel cobalt aluminum oxide (NCA) compound.

[0018] In some embodiments, when the total weight of the dLMFP compound, NMC compound, and NCA compound in the positive electrode active material is regarded as 100 wt%, the dLMFP compound is included in the positive electrode active material in an amount greater than 70 wt%.

[0019] In some embodiments, the amount of the dLMFP compound in the positive electrode active material is 75 wt% or more.

[0020] In some embodiments, the positive electrode active material includes the NMC compound and the NCA compound, and the weight ratio of the NMC compound to the NCA compound (NMC:NCA) is from 1:99 to 99:1.

[0021] In some embodiments, the NMC compound having a Ni content greater than 0.6 relative to the total amount of metals other than Li is a lithiated oxide according to the following formula (2):

[0022] Li (1+x) Ni a Mn b Co c M' d O2 (2),

[0023] wherein, in formula (2):

[0024] 0 ≤ x ≤ 0.15,

[0025] a > 0.6; b > 0; c > 0; d ≥ 0 and a + b + c + d = 1, and

[0026] M' is selected from one or more of B, Mg, Al, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, and Mo.

[0027] In some embodiments, the NMC compound is LiNi 0.605 Mn 0.197 Co 0.198 O2 (also referred to herein as NMC622).

[0028] In some embodiments, the NMC compound is LiNi 0.8 Mn 0.1 Co 0.1O2 (also referred to herein as NMC811).

[0029] In some embodiments, the NCA compound is a lithiated oxide of nickel (Ni), cobalt (Co), and aluminum (Al) according to the following formula (3):

[0030] Li 1+x (Ni a Co b Al c )O2 (3),

[0031] wherein, in formula (3):

[0032] a, b, and c are non-zero,

[0033] a + b + c = 1, and

[0034] 0 ≤ x ≤ 0.15.

[0035] In some embodiments, the NCA compound is LiNi 0.8 Co 0.15 Al 0.05 O2.

[0036] In some embodiments, when both the NMC compound and the NCA compound are included in the blend, the content of Ni in the NMC compound can be 0.6 or less relative to the total amount of metals other than Li.

[0037] In some embodiments, when the blend contains the dLMFP compound and the NMC compound, the weight ratio of dLMFP:NMC can be >70:<30, 75:25, 80:20, 85:15, 90:10, 95:5, 96:4, 97:3, 98:2, or 99:1.

[0038] In some embodiments, when the blend contains the dLMFP compound and the NCA compound, the weight ratio of dLMFP:NCA can be >70:<30, 75:25, 80:20, 85:15, 90:10, 95:5, 96:4, 97:3, 98:2, or 99:1.

[0039] In some embodiments, the positive electrode active material according to the present invention comprises a blend of dLMFP with an NMC compound according to formula (2) and an NCA compound according to formula (3).

[0040] In another embodiment of the present invention, a lithium ion secondary battery is disclosed, which includes a cathode containing the positive electrode active material according to any one of the embodiments of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Any accompanying drawings included in this document are provided only as examples and do not limit the present invention.

[0042] Figure 1A To show the relationship diagram of the voltage (V) and the depth of discharge (DoD) of the half-cell prepared in Example 1.

[0043] Figure 1B To show the relationship diagram of the voltage (V) and the discharge capacity (mAh / g) of the half-cell prepared in Example 1.

[0044] Figure 2A To show the relationship diagram of the voltage (V) and the depth of discharge (DoD) of the half-cell prepared in Example 2.

[0045] Figure 2B To show the relationship diagram of the voltage (V) and the discharge capacity (mAh / g) of the half-cell prepared in Example 2.

[0046] Figure 3 To show the curve diagram of the capacity retention result of the prismatic battery prepared in Example 3.

[0047] Figure 4 To show the relationship diagram of the battery impedance (m ohm) and the capacity (%) of the 45Ah cylindrical battery prepared in Example 4 at 30°C.

[0048] Figure 5 To show the curve diagram of the rate performance of the half-cell prepared in Example 5. Detailed Description of the Invention

[0049] It should be understood that the foregoing general description and the following detailed description are both exemplary and are intended to provide further explanation of the claims. Therefore, various changes, modifications, and equivalents of the methods, devices, and / or systems described herein will be apparent to those of ordinary skill in the art. In addition, descriptions of known functions and structures may be omitted for the sake of clarity and conciseness.

[0050] The terms used in the specification are only intended to describe the embodiments and should in no way be restrictive. Unless otherwise clearly used, expressions in the singular form include the meaning of the plural form. In this specification, for example, expressions such as "comprising" or "including" are intended to specify features, quantities, steps, operations, elements, parts, or combinations thereof, and should not be construed as excluding the possibility of the existence of any one or more other features, quantities, steps, operations, elements, parts, or combinations thereof.

[0051] Any range will be understood to include and disclose each discrete point and sub-range within that range.

[0052] (Positive (cathode) active material)

[0053] The positive (cathode) active material of the present invention comprises a blend of (A) a doped lithium manganese iron phosphate compound (referred to herein as dLMFP) according to the following formula (1) and (B) a lithium nickel cobalt manganese oxide (NMC) compound (the Ni content of which is greater than 0.6 relative to the total amount of metals other than Li) and / or a lithium nickel cobalt aluminum oxide (NCA) compound.

[0054] (dLMFP)

[0055] Lithium manganese iron phosphate (LMFP) compounds and their synthesis are known, for example, as described in the background section above. The doped lithium manganese iron phosphate (dLMFP) compound for use in the positive electrode active material of the present invention is a compound according to the following formula (1):

[0056] LiMn x Fe y M 1-x-y PO4 (1),

[0057] wherein, in formula (1):

[0058] 0.9 < x + y < 1; and

[0059] M is one or more of Co, Ni, V, Y, Mg, Ca, Ba, Al, Sc and Nd.

[0060] In one embodiment of the dLMFP compound according to formula (1), M is one or more of Mg, Ca, Ba. In a preferred embodiment, M is Mg.

[0061] Compared with LMFP, using the dLMFP compound according to formula (1) as the positive electrode active material provides favorable results. For example, it is expected that magnesium-doped LMFP (i.e., the dLMFP compound according to formula (1) where M is Mg) can inhibit the dissolution of Mn and Fe and also improve the electrochemical performance of LMFP.

[0062] The positive electrode active material of the present invention is blended with a lithium nickel cobalt manganese oxide (NMC) compound and / or a lithium nickel cobalt aluminum oxide (NCA) compound.

[0063] NMC and NCA (used alone or together) have a potential equal to or lower than that of dLMFP. Since dLMFP and NMC and / or NCA operate in the same voltage window of the battery, the above potential is defined as the quotient of the total discharge energy (Wh) divided by the total discharge capacity (Ah) of the individual components.

[0064] The dLMFP compound according to Formula (1) has a very flat charge / discharge plateau. This is shown in Figure 1 (discussed further in the examples below). This makes it difficult for the battery management system (BMS) to monitor the state of charge to accurately predict the remaining charge for further utilization. However, it has been found that blending dLMFP with NMC and / or NCA produces voltage slopes at the beginning and end of charge / discharge, which is not only beneficial to the BMS but also improves the energy density. It has also been found that blending dLMFP with NMC and / or NCA can improve the coating quality, adhesion, and electrode density of dLMFP. It has also been found that blending dLMFP with NMC and / or NCA significantly improves the rate performance and cycle life of dLMFP.

[0065] (NMC)

[0066] The NMC compound (or lithiated oxide of Ni, Mn, and Co) for the positive electrode active material according to the present invention can be any known NMC compound used as a positive electrode active material, provided that the content of Ni is greater than 0.6 relative to the total amount of metals other than Li, as described below.

[0067] The NMC compound used as a positive electrode active material and its synthesis are known. For example, the NMC compound disclosed in U.S. Patent Application No. 2018 / 0145314 is incorporated herein by reference in its entirety. In a preferred embodiment, the NMC compound is according to the following Formula (2):

[0068] Li (1+x) Ni a Mn b Co c M' d O2 (2),

[0069] wherein, in Formula (2):

[0070] 0≤x≤0.15,

[0071] a>0.6b>0; c>0; d≥0 and a + b + c + d = 1, and

[0072] M' is selected from one or more of B, Mg, Al, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, and Mo.

[0073] In certain embodiments of the NMC compound according to Formula (2), 0.40>b≥0.15; or 0.35≥b≥0.20.

[0074] In certain embodiments of the NMC compound according to Formula (2), 0.30≥c≥0.10; or 0.25≥c≥0.15.

[0075] In certain embodiments of the NMC compound according to formula (2), x ≤ 0.10; or 0.01 ≤ x ≤ 0.06.

[0076] Specific examples of the NMC compound according to formula (2) are:

[0077] LiNi 0.605 Mn 0.197 Co 0.198 O2 (also referred to herein as NMC622); and

[0078] Li 1+x Ni 0.8 Mn 0.1 Co 0.1 O2 (also referred to herein as NMC811), 0.01 ≤ x ≤ 0.10, preferably 0.01 ≤ x ≤ 0.06.

[0079] In other embodiments of the present invention, when both the NMC compound and the NCA compound are included in the blend, the content of Ni in the NMC compound can be less than or equal to 0.6 relative to the total amount of metals other than Li (for example, when the NCA compound is blended with the dLMFP compound, the NMC compound can be LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 O2).

[0080] (NCA)

[0081] The NCA compound used as the positive electrode active material is known. Any known lithiated oxide of Ni, Co, and Al can be used as the NCA compound. In a preferred embodiment, the NCA compound is LiNi 0.8 Co 0.15 Al 0.05 O2.

[0082] The NCA compound can also be a compound according to the following formula (3):

[0083] Li 1+x (Ni a Co b Al c )O2 (3),

[0084] wherein, in formula (3):

[0085] a, b, and c are non-zero,

[0086] a + b + c = 1, and

[0087] 0 ≤ x ≤ 0.15.

[0088] (Blending Ratio of Cathode Active Material)

[0089] In a preferred embodiment, when the total content of dLMFP, NMC, and NCA in the cathode active material is regarded as 100 wt%, the blend weight ratio of dLMFP to the total amount of NMC and / or NCA (i.e., dLMFP:(NMC + NCA)) is greater than 70 wt% of dLMFP and less than 30 wt% of NMC and / or NCA (or this weight ratio can be simplified to a range of >70:<30 to 99:1). In other preferred embodiments of the cathode active material according to the present invention, the weight ratio of dLMFP:(NMC + NCA) can be 75:25, 80:20, 85:15, 90:10, 95:5, 96:4, 97:3, 98:2, or 99:1.

[0090] When the blend contains dLMFP compound and NMC compound, the weight ratio of dLMFP:NMC can be >70:<30, 75:25, 80:20, 85:15, 90:10, 95:5, 96:4, 97:3, 98:2, or 99:1.

[0091] When the blend contains dLMFP compound and NCA compound, the weight ratio of dLMFP:NCA can be >70:<30, 75:25, 80:20, 85:15, 90:10, 95:5, 96:4, 97:3, 98:2, or 99:1.

[0092] In an embodiment that includes both NMC compound and NCA compound simultaneously, the weight ratio range of NMC to NCA (NMC:NCA) can be 1:99 to 99:1 by weight. In other embodiments, the weight ratio of NMC:NCA can be 1:9 to 9:1, 2:8 to 8:2, 3:7 to 7:3, 4:6 to 6:4, or 1:1.

[0093] (Lithium-Ion Battery)

[0094] The present invention also provides a lithium-ion battery, including a cathode, an anode, and an electrolyte having the cathode active material of the present invention. A separator can be disposed between the anode and the cathode.

[0095] (Cathode)

[0096] There is no particular limitation on the structure of the cathode as long as the cathode contains at least the cathode active material of the present invention on the current collector. The cathode material can also include one or more binder materials and one or more conductive materials.

[0097] In a preferred embodiment, the positive electrode active material of the present invention accounts for 100 wt% of the active material of the cathode material. However, in other embodiments, it is contemplated that the positive electrode material may include another known active material such that the positive electrode active material of the present invention may account for 10 wt% or more of the active material of the cathode material, such as 20 wt% or more, 30 wt% or more, 40 wt% or more, 50 wt% or more, 60 wt% or more, 70% or more, 80% or more, 90% or more, 95% or more, or 99% or more.

[0098] There is no particular limitation on the current collector, and known materials and designs can be used. In a preferred embodiment, the current collector is a two-dimensional conductive carrier (such as a solid or perforated sheet) based on carbon or metal (such as nickel, steel, stainless steel, or aluminum).

[0099] There is no particular limitation on the binder material, and known materials for this function can be used. For example, the binder material may include one or more of the following components: polyvinylidene fluoride (PVdF) and its copolymers, polytetrafluoroethylene (PTFE), polyacrylonitrile (PAN), polymethyl methacrylate or polybutyl methacrylate, polyvinyl chloride (PVC), polyvinylformal, polyester and amide block polyethers, acrylic polymers, methacrylic acid, acrylamide, itaconic acid, sulfonic acid, elastomers, and cellulose compounds.

[0100] Among the elastomers that can be used, mention may be made of ethylene / propylene / diene terpolymer (EPDM), styrene / butadiene copolymer (SBR), acrylonitrile / butadiene copolymer (NBR), styrene / butadiene / styrene block copolymer (SBS) or styrene / acrylonitrile / styrene block copolymer (SIS), styrene / ethylene / butene / styrene copolymer (SEBS), styrene / butadiene / vinylpyridine terpolymer (SBVR), polyurethane (PU), chloroprene rubber, polyisobutylene (PIB), butyl rubber, and mixtures thereof.

[0101] The cellulose compound may be, for example, carboxymethyl cellulose (CMC), hydroxypropyl methyl cellulose (HPMC), hydroxypropyl cellulose (HPC), hydroxyethyl cellulose (HEC), or other cellulose derivatives.

[0102] There is no particular limitation on the conductive material, and any known conductive material can be used. For example, the conductive material may be selected from one of graphite, carbon black, acetylene black (AB), soot, or mixtures thereof.

[0103] To fabricate the cathode, the cathode material can be combined with a binder material and a conductive material and applied to a current collector by known methods. For example, it is contemplated that particles including the cathode material can be formed and pressed onto the current collector by known methods, or a slurry including the cathode material and a solvent can be coated onto the current collector and then dried by known methods.

[0104] There are no particular limitations on the amounts of the binder, conductive material, and other additives. When the total weight of the positive electrode material is regarded as 100 wt%, the amount of the conductive material is preferably 1 wt% to 20 wt% (or any amount within this range, such as 4 wt% to 18 wt%), and the amount of the binder is preferably 1 wt% to 20 wt% (or any amount within this range, such as 1 wt% to 7 wt%).

[0105] (Anode)

[0106] There are no particular limitations on the structure of the negative electrode (or anode), and known anode active materials can be used as long as the materials can act as the negative electrode active materials of a lithium-ion battery. For example, the anode active material can include carbon-based negative electrode active materials (such as graphite and coke), alloy-based negative electrode active materials (such as Si and / or Sn, lithium metal, lithium titanate oxide (LTO)), or mixtures thereof. Similar to the cathode, the anode material can include the anode active material and a binder, and the anode material can be applied to a current collector. In a preferred embodiment, the anode active material of the present invention can account for 50 wt% to 99 wt% of the anode material (or any amount within this range, such as 95 wt% to 99 wt%, or 97 wt% to 99 wt%).

[0107] (Electrolyte)

[0108] The electrolyte can be a known non-aqueous electrolyte, which includes a lithium salt dissolved in a solvent.

[0109] There are no particular limitations on the lithium salt, and known lithium salts for non-aqueous lithium-ion batteries can be used. In a preferred embodiment, the electrolyte salt can include one or more of lithium bis(fluorosulfonyl)imide (“LiFSI”), lithium bis(trifluoromethanesulfonyl)imide (“LiTFSI”), LiBF4, lithium bis(oxalato)borate (“LiBOB”), LiClO4, LiAsF6, LiPF6, LiCF3SO3, lithium 4,5-dicyano-2-(trifluoromethyl)imidazole (“LiTDI”), LiPO2F2, etc.

[0110] In a preferred embodiment, the lithium salt concentration in the electrolyte is greater than 1.0 M, greater than 1.2 M, greater than 1.4 M, greater than 1.5 M, greater than 1.6 M, greater than 1.7 M, greater than 1.8 M, or greater than 2.0 M. In a preferred embodiment, the lithium salt concentration is less than 4.0 M, less than 3.6 M, less than 3.2 M, less than 2.8 M, less than 2.4 M, less than 2.0 M, less than 1.6 M or less than 1.2 M.

[0111] There is no particular limitation on the solvent, and known solvents for non-aqueous lithium ion batteries can be used. The solvent can be a single solvent or a mixture of multiple solvents. The solvent can be selected from common organic solvents, especially saturated cyclic carbonates, unsaturated cyclic carbonates, acyclic (or linear) carbonates, alkyl esters (such as formates, acetates, propionates or butyrates), ethers, lactones (such as γ-butyrolactone, tetrahydrothiophene dioxide, nitrile solvents and mixtures thereof). Among these saturated cyclic carbonates, for example, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) and mixtures thereof can be specifically mentioned. Among the unsaturated cyclic carbonates, for example, vinylene carbonate (VC), its derivatives and mixtures thereof can be specifically mentioned. Among the acyclic carbonates, for example, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dipropyl carbonate (DPC) and mixtures thereof can be specifically mentioned. Among the alkyl esters, for example, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate and mixtures thereof can be specifically mentioned. Among the ethers, for example, dimethyl ether (DME) or diethyl ether (DEE) and mixtures thereof can be mentioned. Known fluorinated solvents can also be used, including, for example, fluorinated benzenes (such as hexafluorobenzene, pentafluorobenzene, 1,2,3,4-tetrafluorobenzene, etc.), fluorine-substituted linear carbonates, etc.

[0112] The electrolyte can include known additives for non-aqueous lithium ion batteries.

[0113] An additive that can be included in the electrolyte is a gas generating agent for implementing a pressure type current interrupt device (CID). Exemplary gas generating agents include cyclohexylbenzene (CHB), biphenyl and fluorinated biphenyl, the oxidation potential of which is lower than the oxidation potential of the solvent in the electrolyte. When the lithium ion battery reaches an overcharged state, this compound will react to generate gas before the electrolyte decomposes. When included, the amount of the gas generating agent is preferably 0.01 wt% to 10 wt% (or any amount within this range, such as 0.1 wt% to 5 wt%, or 1 wt% to 3 wt%).

[0114] The use of known fluorinated compound additives can also be specifically mentioned. For example, the electrolyte can include the commonly used additive fluoroethylene carbonate (FEC). When included, FEC (and / or another additive) can be added to the solvent in an amount of 0.1 to 10 wt% based on the total weight of the solvent, or any amount within this range can be added, such as 1 to 10 wt%, 2 to 9 wt%, 3 to 8 wt%, 4 to 7 wt%, 5 to 6 wt%, 1 to 5 wt%, 1 to 4 wt%, 1 to 3 wt%, 1 to 2 wt%, 2 to 3 wt%, or 0.1 to 1 wt%.

[0115] (Separator)

[0116] There are no particular restrictions on the separator, and known separators for non-aqueous lithium ion batteries can be used. The separator allows Li + to pass through and prevents electrical contact between the anode and the cathode. In one embodiment, the separator is a microporous membrane made of a polyolefin-based material, such as a microporous membrane made of polyethylene (PE), polypropylene (PP), etc.

[0117] Examples

[0118] Hereinafter, although the embodiments of the present invention are further described in detail by way of examples, the present invention is not limited thereto.

[0119] (Example 1)

[0120] In Example 1, Cells 1A, 1B, 1C, 1D, and 1E were prepared, and the relationships between voltage (V) and depth of discharge (DoD) (%), and capacity (mAh / g) were measured, and dLMFP was compared with dLMFP blended with NMC622 (LiNi 0.605 Mn 0.197 Co 0.198 O2). Each cell used lithium metal as the anode and an electrolyte containing 1 M LiPF6 in a mixed organic solvent (volume ratio of EC / EMC / DMC is 1:1:1). The only difference between these cells was the positive electrode active material. For Cell 1A, the positive electrode active material was pure magnesium-doped LMFP (LiMn 0.75 Fe 0.2 Mg 0.05 PO4). For Cell 1B, the same magnesium-doped LMFP compound used in Cell 1A was mixed with an NMC compound (LiNi 0.605 Mn 0.197 Co 0.198Blended with O2 (or NMC622), the weight ratio of dLMFP:NMC is 90:10. For Cell 1C, the same magnesium-doped LMFP compound used in Cell 1A is blended with NMC622, and the weight ratio of dLMFP:NMC is 70:30. For Cell 1D, the same magnesium-doped LMFP compound used in Cell 1A is blended with NMC622, and the weight ratio of dLMFP:NMC is 40:60. For Cell 1E, the same magnesium-doped LMFP compound used in Cell 1A is blended with NMC622, and the weight ratio of dLMFP:NMC is 10:90. The summary of Cells 1A to 1E is shown in Table 1. Cells 1A and 1B were discharged at a constant rate (0.1C) at a temperature of about 25 °C to measure the relationship between voltage (V), depth of discharge (DoD) (%), and capacity (mAh / g). The results of Example 1 are shown in Figure 1A and Figure 1B in.

[0121] Table 1

[0122] Battery Anode Cathode Electrolyte Battery 1A Lithium metal dLMFP <![CDATA[1 M LiPF6 in EC / EMC / DMC (1:1:1)]]> Battery 1B Lithium metal dLMFP:NMC622(90:10) <![CDATA[1 M LiPF6 in EC / EMC / DMC (1:1:1)]]> Battery 1C Lithium metal dLMFP:NMC622(70:30) <![CDATA[1 M LiPF6 in EC / EMC / DMC (1:1:1)]]> Battery 1D Lithium metal dLMFP:NMC622(40:60) <![CDATA[1 M LiPF6 in EC / EMC / DMC (1:1:1)]]> Battery 1E Lithium metal dLMFP:NMC622(10:90) <![CDATA[1 M LiPF6 in EC / EMC / DMC (1:1:1)]]>

[0123] As Figure 1A shown, pure dLMFP has a very flat discharge platform, which will make it difficult for the BMS to monitor the state of charge, such as predicting the remaining energy for further utilization. However, Figure 1A it is also shown that adding NMC622 (10 wt% to 90 wt%) produces a voltage slope at both the start and end of the charge / discharge characteristics. This is not only beneficial to the BMS but also improves the energy density (as Figure 1B shown), because NMC622 has a higher capacity compared to dLMFP. The results exceeded expectations.

[0124] (Example 2)

[0125] In Example 2, Cells 2A - 2E were prepared in the same manner as in Example 1, except that for the cells with the active material blend, Li1Ni 0.8 Mn 0.1 Co 0.1 O2 (or NMC811) was used instead of NMC622. Cell 2A includes the same pure magnesium-doped dLMFP as in Example 1, and Cells 2B - 2E include blends of magnesium-doped dLMFP and NMC811. The summary of Cells 2A - 2E is shown in Table 2. The results of Example 2 are shown in Figure 2A and Figure 2B in.

[0126] Table 2

[0127] Battery Anode Cathode Electrolyte Battery 2A Lithium metal dLMFP <![CDATA[1 M LiPF6 in EC / EMC / DMC (1:1:1)]]> Battery 2B Lithium metal dLMFP:NMC811(90:10) <![CDATA[1 M LiPF6 in EC / EMC / DMC (1:1:1)]]> Battery 2C Lithium metal dLMFP:NMC811(70:30) <![CDATA[1 M LiPF6 in EC / EMC / DMC (1:1:1)]]> Battery 2D Lithium metal dLMFP:NMC811(40:60) <![CDATA[1 M LiPF6 in EC / EMC / DMC (1:1:1)]]> Battery 2E Lithium metal dLMFP:NMC811(10:90) <![CDATA[1 M LiPF6 in EC / EMC / DMC (1:1:1)]]>

[0128] As Figure 2A shown, pure dLMFP has a very flat discharge plateau, which will make it difficult for the BMS to monitor the state of charge, such as predicting the remaining energy for further utilization. However, Figure 2A it is also shown that adding NMC811 (10 wt% to 90 wt%) generates a voltage slope at the start and end of the charge / discharge characteristics. This is not only beneficial to the BMS, but also improves the energy density (as Figure 2B shown), because NMC811 has a higher capacity compared to dLMFP. The results exceeded expectations.

[0129] (Example 3)

[0130] In Example 3, a prismatic battery 3A and a battery 3B were prepared, and the capacity after about 400 cycles was measured. Each battery used graphite as the anode and the same electrolyte as in batteries 1A and 1B of Example 1. The only difference between battery 3A and battery 3B was the cathode active material. Battery 3A used the same magnesium-doped LMFP compound as in Example 1. For battery 3B, the same magnesium-doped LMFP compound was blended with an NCA compound (Li 1.04 Ni 0.8 Co 0.15 Al 0.05 O2), and the weight ratio of dLMFP:NCA was 90:10. A summary of battery 3A and battery 3B is shown in Table 3. The measurement was carried out by repeatedly charging and discharging the battery. Both battery 3A and battery 3B had exactly the same battery format, the same electrolyte, the same anode, and the same loading of both electrodes. Except that 10% of the NCA in battery 3B was replaced with the same amount of dLMFP, the rest in the two batteries was the same. The results of Example 3 are shown in Figure 3 (battery 3A = green line; battery 3B = orange line).

[0131] Table 3

[0132] Battery Anode Cathode Electrolyte Battery 4A Graphite dLMFP <![CDATA[1 M LiPF6 in EC / EMC / DMC (1:1:1)]]> Battery 4B Graphite dLMFP:NCA(90:10) <![CDATA[1 M LiPF6 in EC / EMC / DMC (1:1:1)]]>

[0133] As Figure 3 shown, adding NCA as a minor component (10 wt%) provided a significantly improved capacity and better cycle life. The results exceeded expectations.

[0134] (Example 4)

[0135] In Example 4, cylindrical cells 4A and 4B with a capacity of 45 Ah were prepared to measure the relationship between cell impedance (m ohm) and capacity (%). Each cell used graphite as the anode and the same electrolyte as in cells 1A and 1B of Example 1. The only difference between cells 4A and 4B was the positive electrode active material. Cells 4A and 4B used the same positive electrode active materials as cells 3A and 3B in Example 3, respectively. A summary of cells 4A and 4B is shown in Table 4. The cells were cycled between 2.7 and 4.2 V. The cells tested here are the same as those in Figure 3 .

[0136] The results of Example 4 are shown in Figure 4 (Cell 4A = red line; Cell 4B = black line).

[0137] Table 4

[0138] Battery Anode Cathode Electrolyte Battery 5A Graphite dLMFP <![CDATA[1 M LiPF6 in EC / EMC / DMC (1:1:1)]]> Battery 5B Graphite dLMFP:NCA(90:10) <![CDATA[1 M LiPF6 in EC / EMC / DMC (1:1:1)]]>

[0139] As Figure 4 shown, adding NCA as a minor component (10 wt%) provided a significantly reduced internal impedance. The results exceeded expectations.

[0140] (Example 5)

[0141] In Example 5, cells 5A, 5B, and 5C were prepared to measure the rate performance. Each cell used graphite as the anode and the same electrolyte as in Example 1. The only difference between cells 5A, 5B, and 5C was the positive electrode active material. Each cell used the same magnesium-doped dLMFP compound as in Example 1. Cell 5A used pure dLMFP. Cell 5B blended dLMFP with the NCA compound used in Example 3, with a weight ratio of dLMFP:NCA of 90:10. Cell 5C blended dLMFP with the same NCA compound used in Example 3, with a weight ratio of dLMFP:NCA of 75:25. A summary of cells 5A to 5C is shown in Table 5. The results are shown in Figure 5 (Cell 5A = yellow line; Cell 5B = blue line; Cell 5C = red line).

[0142] Table 5

[0143] Battery Anode Cathode Electrolyte Battery 6A Graphite dLMFP <![CDATA[1 M LiPF6 in EC / EMC / DMC (1:1:1)]]> Battery 6B Graphite dLMFP:NCA(90:10) <![CDATA[1 M LiPF6 in EC / EMC / DMC (1:1:1)]]> Battery 6C Graphite dLMFP:NCA(75:25) <![CDATA[1 M LiPF6 in EC / EMC / DMC (1:1:1)]]>

[0144] As Figure 5 shown, adding NCA as a minor component (10 wt% or 25 wt%) provided improved rate performance. The results exceeded expectations.

[0145] The present invention is susceptible to various modifications and alternative means, and specific embodiments thereof are described in detail herein. However, it should be understood that the present invention is not limited to the specific embodiments or methods disclosed, and on the contrary, the present invention will cover all modifications, equivalents, and alternatives falling within the spirit and scope of the claims.

Claims

1. A positive electrode active material for a lithium ion secondary battery, the positive electrode active material comprising LiMn 0.75 Fe 0.2 Mg 0.05 PO4 and a blend of a lithium nickel manganese cobalt oxide compound or Li 1.04 Ni 0.8 Co 0.15 Al 0.05 O2, wherein, The lithium nickel manganese cobalt oxide compound is LiNi 0.605 Mn 0.197 Co 0.198 O2 or Li1Ni 0.8 Mn 0.1 Co 0.1 O2, Wherein when the total weight of LiMn 0.75 Fe 0.2 Mg 0.05 PO4 and the lithium nickel manganese cobalt oxide compound or Li 1.04 Ni 0.8 Co 0.15 Al 0.05 O2 is regarded as 100 wt%, the weight ratio of LiMn 0.75 Fe 0.2 Mg 0.05 PO4 and the lithium nickel manganese cobalt oxide compound or Li 1.04 Ni 0.8 Co 0.15 Al 0.05 O2 is 90:10 to 99:

1.

2. A lithium ion secondary battery, comprising: A cathode, comprising the positive electrode active material according to claim 1, An anode, comprising a negative electrode active material, and An electrolyte, comprising a lithium salt and an organic solvent.

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