Positive electrode material, positive electrode sheet and lithium ion battery

Abstract

A positive electrode material, a positive electrode sheet and a lithium ion battery. The positive electrode material is a mixture of a lithium manganese iron phosphate material and a ternary material, and during mixing, a mass ratio n of the ternary material to the lithium manganese iron phosphate material in the positive electrode material is determined on the basis of the range of a ratio k of actual gram capacities of the ternary material and the lithium manganese iron phosphate material. Specifically, when k is less than 1.34, n is 1-9; and when k is greater than 1.34, n is 0.1-1, which can avoid the occurrence of the following situations: due to an improper mixing ratio of the two materials, the lithium ion battery prepared using the positive electrode material is prone to problems such as low capacity retention rate, low cycle retention rate, and serious cycle gas generation. The lithium ion battery prepared from the positive electrode material may have high energy density, high capacity retention rate, good cycle performance and good safety performance at the same time.

Description

Positive electrode material, positive electrode sheet, and lithium-ion battery Technical Field

[0001] The embodiments of the present invention relate to, but are not limited to, the technical field of lithium-ion batteries, and specifically, to a positive electrode material, a positive electrode sheet, and a lithium-ion battery. Background Art

[0002] Lithium iron manganese phosphate (LiMnPO4) balances safety and low cost. By increasing the voltage platform through dissolved manganese, it increases energy density by 10% to 20%. However, this comes at the expense of the material's cycling and rate performance. Currently, not only is the dissolved manganese content inconsistent, but there's also no fixed method for its application. Ternary materials are relatively expensive, and compared to high-nickel ternary materials, medium-nickel ternary materials have lower energy density. Energy density is typically increased by increasing voltage at the expense of long-term performance. High-nickel ternary materials offer higher energy density, but current safety concerns limit their rapid adoption.

[0003] By blending lithium iron manganese phosphate and ternary materials to form a composite positive electrode system, balanced energy density and safety performance can be achieved. However, at present, for the positive electrode material obtained by blending lithium iron manganese phosphate and ternary materials, when the blending ratio of the two materials is not appropriate, the lithium-ion battery made using the positive electrode material is prone to problems such as low capacity retention rate, low cycle retention rate, and high cycle gas production. In addition, for the positive electrode material obtained by blending lithium iron manganese phosphate and ternary materials, it is difficult for the lithium-ion battery made using the positive electrode material to have suitable energy density, high capacity retention rate, high cycle retention rate, and low cycle gas production at the same time.

[0004] Summary of the Invention

[0005] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0006] The embodiment of the present invention provides a positive electrode material, which includes w1 parts of active material A Li i1 Mn x1 Fe y1 PO4M f1 and w2 parts of B active material Li i2 Ni x2 Co y2 Mn z O2H f2 ,

[0007] wherein i1 is 0.95 to 1.1, the ratio of x1 to y1 is 0.5 to 4, the sum of x1 and y1 is 1, f1 is 200 ppm to 3000 ppm, and M includes at least one of V, Al, Mo, Zr, Mg, Ti, W, Sr, Cr, La, and Ce; i2 is 0.95 to 1.1, the sum of x2, y2, and z is 1, f2 is 200 ppm to 8000 ppm, and H includes at least one of Al, Zr, Ti, Mg, Sr, W, Y, Nb, Ca, Mo, B, F, Ge, Sn, Ce, and Ta;

[0008] The actual gram capacity of the active substance A is c1, the actual gram capacity of the active substance B is c2, the ratio of c2 to c1 is k, and the ratio of w2 to w1 is n; when k is less than or equal to 1.34, n is 1 to 9; when k is greater than 1.34, n is 0.1 to 1.

[0009] Optionally, the D50 of the active substance A is 0.2 μm to 5 μm, and the specific surface area is not higher than 25 m 2 / g, the D50 of the B active substance is 2μm to 13μm, and the specific surface area is not higher than 1.5m 2 / g.

[0010] Optionally, the particle size distribution of the active substance A satisfies the following relationship: (D90-D50) / (D90-D10)≤0.96; 0.03≤(D50-D10) / (D90-D50)≤0.24.

[0011] Optionally, the particle size distribution of the active substance B satisfies the following relationship: (D50-D10) / (D90-D10)≤0.40; 0.35≤(D50-D10) / (D90-D50)≤0.75.

[0012] Optionally, the physical property parameters of the active material A and the active material B satisfy the following relationship: 0.95≤(T1*T2*S1*S2) / (D1*D2*P1*P2)≤1.15;

[0013] Wherein, T1 and T2 are the tap densities of the active material A and the active material B, respectively; D1 and D2 are the D50 of the active material A and the active material B, respectively; P1 and P2 are the powder compaction densities of the active material A and the active material B, respectively; S1 and S2 are the specific surface areas of the active material A and the active material B, respectively.

[0014] Optionally, the three strongest peaks of the XRD spectrum of the active material A satisfy the following relationship: 0.99≤I a1 / I a2≤1.39, 0.74≤F a1 / F a2 ≤1.14, 1.07≤I a1 / I a3 ≤1.47, 0.82≤F a1 / F a3 ≤1.22;

[0015] Among them, I a1 , I a2 , I a3 are the intensity of the first strong peak, the intensity of the second strong peak, and the intensity of the third strong peak of the active substance A, respectively. a1 、F a2 、F a3 are the half-peak width of the first strong peak, the half-peak width of the second strong peak, and the half-peak width of the third strong peak of the active substance A, respectively;

[0016] The three strong peaks of the XRD spectrum of the active material B satisfy the following relationship: 1.23≤I b1 / I b2 ≤1.63, 0.6≤F b1 / F b2 ≤1.0,3.45≤I b1 / I b3 ≤3.85, 0.67≤F b1 / F b3 ≤1.07;

[0017] Among them, I b1 , I b2 , I b3 are the intensity of the first strong peak, the intensity of the second strong peak, and the intensity of the third strong peak of the B active substance, respectively. b1 、F b2 、F b3 are the half-value width of the first strong peak, the half-value width of the second strong peak, and the half-value width of the third strong peak of the B active substance, respectively.

[0018] An embodiment of the present invention further provides a positive electrode plate, comprising the positive electrode material as described above.

[0019] An embodiment of the present invention further provides a lithium-ion battery comprising the positive electrode plate described above.

[0020] Optionally, the compaction density of the positive electrode sheet is 2.0 g / cm 3 to 3.6g / cm 3 .

[0021] Optionally, during the preparation of the lithium-ion battery, the electrolyte injection coefficient is h, the ratio of the negative electrode capacity to the positive electrode capacity of the lithium-ion battery is q, and the ratio of h to q is 2.43 to 3.48.

[0022] Compared with the prior art, the embodiment of the present invention adopts a mixture of lithium manganese iron phosphate material (active material A) and a ternary positive electrode material (active material B) as the positive electrode material. The overall proportion of transition metal ions in the positive electrode sheet obtained by mixing the lithium manganese iron phosphate material and the ternary positive electrode material with the element ratio defined in the embodiment of the present invention as the positive electrode active material is moderate. At the same time, in the embodiment of the present invention, when the lithium manganese iron phosphate material and the ternary material are blended, the mass ratio n of the ternary material and the lithium manganese iron phosphate material in the positive electrode material is determined according to the range of the ratio k of the actual gram capacity of the ternary material and the lithium manganese iron phosphate material. Specifically, when k is below 1.34, n is 1 to 9; when k is greater than 1.34, n is 0.1 to 1, which can avoid the following situation: due to the improper blending ratio of the two materials, the lithium ion battery made using the positive electrode material is prone to problems such as low capacity retention rate, low cycle retention rate, and severe cycle gas production. As a result, the lithium-ion battery made of the positive electrode material may have higher energy density, higher capacity retention rate, higher cycle retention rate and lower cycle gas production.

[0023] Still other aspects will become apparent upon reading and understanding the detailed description. DETAILED DESCRIPTION

[0024] In order to make the above-mentioned objects, features and advantages of the embodiments of the present invention more obvious and easy to understand, specific embodiments of the present invention are described in detail below.

[0025] It should be noted that, unless otherwise specified, the features of the embodiments of the present invention may be combined with each other. The terms "comprising," "including," "containing," and "having" are non-restrictive and may include other steps and other ingredients that do not affect the results. The above terms encompass the terms "consisting of" and "consisting essentially of." Unless otherwise specified, materials, equipment, and reagents are commercially available. It should also be noted that, in the embodiments of the present invention, ppm means parts per million.

[0026] The embodiment of the present invention provides a positive electrode material, which comprises w1 parts of active material A Li i1 Mn x1 Fe y1 PO4M f1 and w2 parts of B active material Li i2 Ni x2 Co y2 Mn z O2H f2,

[0027] wherein i1 is 0.95 to 1.1, the ratio of x1 to y1 is 0.5 to 4, the sum of x1 and y1 is 1, f1 is 200 ppm to 3000 ppm, M includes at least one of V, Al, Mo, Zr, Mg, Ti, W, Sr, Cr, La and Ce; i2 is 0.95 to 1.1, the sum of x2, y2 and z is 1, f2 is 200 ppm to 8000 ppm, H includes at least one of Al, Zr, Ti, Mg, Sr, W, Y, Nb, Ca, Mo, B, F, Ge, Sn, Ce and Ta;

[0028] The actual gram capacity of the active substance A is c1, the actual gram capacity of the active substance B is c2, the ratio of c2 to c1 is k, and the ratio of w2 to w1 is n; when k is less than or equal to 1.34, n is 1 to 9; when k is greater than 1.34, n is 0.1 to 1.

[0029] Compared with the prior art, the present embodiment adopts a mixture of lithium manganese iron phosphate material (active material A) and a ternary positive electrode material (active material B) as the positive electrode material. The overall proportion of transition metal ions in the positive electrode sheet obtained by mixing the lithium manganese iron phosphate material and the ternary positive electrode material with the element ratio defined in the embodiment of the present invention as the positive electrode active material is moderate. At the same time, in the present embodiment, when the lithium manganese iron phosphate material and the ternary material are blended, the mass ratio n of the ternary material and the lithium manganese iron phosphate material in the positive electrode material is determined according to the range of the ratio k of the actual gram capacity of the ternary material and the lithium manganese iron phosphate material. Specifically, when k is below 1.34, n is 1 to 9; when k is greater than 1.34, n is 0.1 to 1, which can avoid the following situation: due to the improper blending ratio of the two materials, the lithium ion battery made using the positive electrode material is prone to problems such as low capacity retention, low capacity retention, and severe cycle gas production. As a result, the lithium-ion battery made of the positive electrode material may have higher energy density, higher capacity retention rate, higher cycle retention rate and lower cycle gas production.

[0030] In this embodiment, the active material A is Li i1 Mn x1 Fe y1 PO4M f1 The actual gram capacity c1 is obtained by the button test method. The following describes the test method using the 2032 button battery as an example. The specific process is as follows:

[0031] Active material A was used as the positive electrode active material to prepare button cells. Ten cells were tested for gram capacity. The average of the obtained battery gram capacity data was taken to obtain the actual gram capacity c1 of active material A. The process parameters involved in the preparation of the 2032-type button cell are as follows: positive electrode formula: conductive agent SP: binder PVDF: positive electrode active material = 4:4:92, positive electrode current collector is aluminum foil, counter electrode is metal Li, the electrolyte used is hexafluorophosphoric acid, and the separator used is Celgard2400. The positive electrode slurry coating surface density is controlled at 8.75±0.1mg / cm 2 The compaction density of the positive electrode is 1.6g / cm 3 .

[0032] The gram capacity test method for a single battery is as follows:

[0033] At 25±2℃, the half-battery is charged to V1 at a constant current of 0.1C, charged to 0.05C at a constant voltage of V1, and then discharged to V2 at a constant current of 0.1C. This cycle is repeated twice. The gram capacity of the battery is calculated based on the second discharge capacity value. The calculation formula is as follows: C=C 放电 / [(M 电极 -M 铝箔 )*0.92];

[0034] Among them, C 放电 is the capacity of half-battery after two cycles, M 电极 is the mass of the positive electrode, M 铝箔 The mass of the current collector aluminum foil in the positive electrode sheet, V1 is 4.5V, and V2 is 2V.

[0035] In this embodiment, the active material B Li i2 Ni x2 Co y2 Mn z O2H f2 The actual gram capacity c2 is obtained by the button test method. The following describes the test method using the 2032 button battery as an example. The specific process is as follows:

[0036] Using active material B as the positive electrode active material, button cells were prepared. Ten cells were tested for gram capacity. The average of the obtained battery gram capacity data was taken to obtain the actual gram capacity c2 of active material B. The process parameters involved in the preparation of the 2032 button cell are as follows: positive electrode formula: conductive agent SP: binder PVDF: positive electrode active material = 4:4:92, positive electrode current collector is aluminum foil, counter electrode is metal Li, the electrolyte used is hexafluorophosphoric acid, and the separator used is Celgard2400. The positive electrode slurry coating surface density is controlled at 8.75±0.1mg / cm 2 The compaction density of the positive electrode is 2.6g / cm 3.

[0037] The gram capacity test method for a single battery is as follows:

[0038] At 25±2℃, the half-battery is charged to V1 at a constant current of 0.1C, charged to 0.05C at a constant voltage of V1, and then discharged to V2 at a constant current of 0.1C. This cycle is repeated twice. The gram capacity of the battery is calculated based on the second discharge capacity value. The calculation formula is as follows: C=C 放电 / [(M 电极 -M 铝箔 )*0.92];

[0039] Among them, C 放电 is the capacity of half-battery after two cycles, M 电极 is the mass of the positive electrode, M 铝箔 The mass of the current collector aluminum foil in the positive electrode sheet, when x2 is less than 0.8, V1 is 4.4V, V2 is 3.0V, when x2 is greater than or equal to 0.8, V1 is 4.3V, V2 is 3.0V.

[0040] In some embodiments of the present invention, the D50 of the active substance A is 0.2-5 μm, and the specific surface area is not higher than 25 m 2 / g, the particle size distribution of the active substance A satisfies the following relationship: (D90-D50) / (D90-D10)≤0.96; 0.03≤(D50-D10) / (D90-D50)≤0.24.

[0041] Active material A has poor conductivity, and the presence of a large number of large particles in active material A can lead to a longer lithium ion transmission path and increased impedance, thereby affecting the capacity of active material A. In the embodiments of the present invention, by controlling the particle size and particle size distribution of active material A in the positive electrode material, the presence of a large number of large particles of active material A in the positive electrode material is avoided, thereby fully utilizing the high energy density advantage of active material A and ensuring that the lithium-ion battery manufactured using this positive electrode material has a relatively suitable energy density.

[0042] In some embodiments of the present invention, the D50 of the active substance B is 2-13 μm, and the specific surface area is not higher than 1.5 m 2 / g, the particle size distribution of the active substance B satisfies the following relationship: (D50-D10) / (D90-D10)≤0.40; 0.35≤(D50-D10) / (D90-D50)≤0.75.

[0043] When the number of small particles of active material B increases, side reactions will increase, leading to an increase in the gas production of the lithium-ion battery cycle. In the embodiments of the present invention, by controlling the particle size and particle size distribution of the active material B in the positive electrode material, the presence of a large number of small particles of active material B in the positive electrode material is avoided.

[0044] In some embodiments of the present invention, the physical properties of the active material A and the active material B satisfy the following relationship: 0.95≤(T1*T2*S1*S2) / (D1*D2*P1*P2)≤1.15,

[0045] Wherein, T1 and T2 are the tap densities of active material A and active material B, respectively; D1 and D2 are the D50 of active material A and active material B, respectively; P1 and P2 are the powder compaction densities of active material A and active material B, respectively; S1 and S2 are the specific surface areas of active material A and active material B, respectively.

[0046] In some embodiments of the present invention, the three strongest peaks of the XRD spectrum of the active material A satisfy the following relationship: 0.99≤I a1 / I a2 ≤1.39, 0.74≤F a1 / F a2 ≤1.14, 1.07≤I a1 / I a3 ≤1.47, 0.82≤F a1 / F a3 ≤1.22;

[0047] Among them, I a1 , I a2 , I a3 are the intensity of the first strong peak, the intensity of the second strong peak, and the intensity of the third strong peak of the active substance A, respectively. a1 、F a2 、F a3 are the half-peak width of the first strong peak, the half-peak width of the second strong peak, and the half-peak width of the third strong peak of the active substance A, respectively;

[0048] The three strong peaks of the XRD spectrum of the active material B satisfy the following relationship: 1.23≤I b1 / I b2 ≤1.63, 0.6≤F b1 / F b2 ≤1.0,3.45≤I b1 / I b3 ≤3.85, 0.67≤F b1 / F b3 ≤1.07;

[0049] Among them, I b1 , Ib2 , I b3 are the intensity of the first strong peak, the intensity of the second strong peak, and the intensity of the third strong peak of the B active substance, respectively. b1 、F b2 、F b3 are the half-value width of the first strong peak, the half-value width of the second strong peak, and the half-value width of the third strong peak of the B active substance, respectively.

[0050] The triple peak intensity and half-peak width of the material reflect the crystallinity of the material, and the crystallinity of the material affects the performance of the material.

[0051] An embodiment of the present invention further provides a positive electrode plate, comprising the positive electrode material as described above.

[0052] The embodiment of the present invention further provides a lithium ion battery, comprising the positive electrode sheet as described above, wherein the compaction density of the positive electrode sheet is 2.0 g / cm 3 to 3.6g / cm 3 ; The electrolyte injection coefficient of the lithium-ion battery during the preparation process is h, the ratio of the negative electrode capacity to the positive electrode capacity of the lithium-ion battery is q, and the ratio of h to q is 2.43 to 3.48.

[0053] The present invention will be further described below with reference to specific examples. It should be understood that these examples are only intended to illustrate the present invention and are not intended to limit the scope of the present invention.

[0054] Example 1

[0055] In parts by weight, the positive electrode material in this embodiment includes w1 parts of active material A LiMn 0.6 Fe 0.4 PO4M f1 and w2 parts of B active material LiNi 0.9 Co 0.05 Mn 0.05 O2H f2 , where f1 is 500ppm, M is Ti; f2 is 2000ppm, H is Zr.

[0056] After testing, the actual gram capacity c1 of active material A is 152 mAh / g, the actual gram capacity c2 of active material B is 220 mAh / g, the ratio of c2 to c1 is k, and the ratio of w2 to w1 is n;

[0057] In this embodiment, k is 1.45, n is 0.25, D90 of active material A is 4.72 μm, D50 is 0.556 μm, D10 is 0.302 μm, (D90-D50) / (D90-D10) is 0.94 and (D50-D10) / (D90-D50) is 0.06, and the particle size distribution satisfies the following relationship: (D90-D50) / (D90-D10)≤0.96, 0.03≤(D50-D10) / (D90-D50)≤0.24;

[0058] Active material B has D90 = 6.939 μm, D50 = 3.917 μm, D10 = 2.158 μm, (D50-D10) / (D90-D10) = 0.36 and (D50-D10) / (D90-D50) = 0.56, and a particle size distribution that satisfies the following relationship: (D50-D10) / (D90-D10) ≤ 0.40 and 0.35 ≤ (D50-D10) / (D90-D50) ≤ 0.75

[0059] In this embodiment, the physical properties of the active material A and the active material B satisfy the following relationship: 0.95≤(T1*T2*S1*S2) / (D1*D2*P1*P2)≤1.15;

[0060] Wherein, T1 and T2 are the tap densities of active material A and active material B, respectively; D1 and D2 are the D50 of active material A and active material B, respectively; P1 and P2 are the powder compaction densities of active material A and active material B, respectively; S1 and S2 are the specific surface areas of active material A and active material B, respectively. Specifically, in this embodiment: T1 and T2 are 0.593 g / cm 3 、1.93g / cm 3 , D1 and D2 are 0.556μm and 3.917μm respectively, P1 and P2 are 2.205g / cm 3 、3.127g / cm 3 , S1 and S2 are 19.43m respectively 2 / g, 0.716m 2 / g.

[0061] The relationship between the three peak intensities of the XRD spectrum of the active material A is: ①I a1 / I a2 =1.19, F a1 / F a2 =0.94,②I a1 / I a3 =1.27, F a1 / F a3 =1.02;

[0062] The three strongest peaks satisfy the following relationship: 0.99≤I a1 / I a2 ≤1.39, 0.74≤F a1 / F a2 ≤1.14, 1.07≤I a1 / I a3 ≤1.47, 0.82≤F a1 / F a3 ≤1.22;

[0063] Among them, I a1 , I a2 , I a3 are the intensity of the first, second and third strongest peaks of active substance A, respectively, and F a1 、F a2 、F a3 are the half-peak width of the first strong peak, the half-peak width of the second strong peak, and the half-peak width of the third strong peak of active substance A respectively;

[0064] The relationship between the three peak intensities of the XRD spectrum of the B active material is: b1 / I b2 =1.43, F b1 / F b2 =0.8,②I b1 / I b3 =3.65, F b1 / F b3 =0.87,

[0065] The three strongest peaks satisfy the following relationship: 1.23≤I b1 / I b2 ≤1.63, 0.6≤F b1 / F b2 ≤1.0,3.45≤I b1 / I b3 ≤3.85, 0.67≤F b1 / F b3 ≤1.07;

[0066] Among them, I b1 , I b2 , I b3 are the intensity of the first strong peak, the intensity of the second strong peak, and the intensity of the third strong peak of the B active substance, respectively. b1 、F b2 、F b3 are the half-value width of the first strong peak, the half-value width of the second strong peak, and the half-value width of the third strong peak of the B active substance, respectively.

[0067] The positive electrode material in this embodiment is used to prepare a lithium ion battery. During the preparation of the lithium ion battery, the positive electrode coating double-sided density is 372g / m 2 The compaction density of the positive electrode sheet after roller pressing is 2.5g / cm 3 The electrolyte injection coefficient h is 3.6, the ratio q of the negative electrode capacity to the positive electrode capacity of the lithium ion battery is 1.08, and the ratio of h to q is 3.3.

[0068] Example 2

[0069] In parts by weight, the positive electrode material in this embodiment includes w1 parts of active material A LiMn 0.6 Fe 0.4 PO4M f1 and w2 parts of B active material LiNi 0.6 Co 0.1 Mn 0.3 O2H f2 , where f1 is 500ppm, M is Ti; f2 is 2000ppm, H is Zr.

[0070] After testing, the actual gram capacity c1 of active material A is 152 mAh / g, the actual gram capacity c2 of active material B is 197 mAh / g, the ratio of c2 to c1 is k, and the ratio of w2 to w1 is n;

[0071] In this embodiment, k is 1.30, n is 4, D90 of active material A is 4.72 μm, D50 is 0.556 μm, D10 is 0.302 μm, (D90-D50) / (D90-D10) is 0.94 and (D50-D10) / (D90-D50) is 0.06, and the particle size distribution satisfies the following relationships: (D90-D50) / (D90-D10)≤0.96; 0.03≤(D50-D10) / (D90-D50)≤0.24;

[0072] The D90 of active substance B is 6.920 μm, D50 is 3.920 μm, D10 is 2.155 μm, (D50-D10) / (D90-D10) is 0.37 and (D50-D10) / (D90-D50) is 0.59, and the particle size distribution satisfies the following relationships: (D50-D10) / (D90-D10)≤0.40; 0.35≤(D50-D10) / (D90-D50)≤0.75.

[0073] In this embodiment, the physical properties of the active material A and the active material B satisfy the following relationship: 0.95≤(T1*T2*S1*S2) / (D1*D2*P1*P2)≤1.15;

[0074] Wherein, T1 and T2 are the tap densities of active material A and active material B, respectively; D1 and D2 are the D50 of active material A and active material B, respectively; P1 and P2 are the powder compaction densities of active material A and active material B, respectively; S1 and S2 are the specific surface areas of active material A and active material B, respectively. Specifically, in this embodiment: T1 and T2 are 0.593 g / cm 3 , 1.928g / cm 3 , D1 and D2 are 0.556μm and 3.920μm respectively, P1 and P2 are 2.205g / cm 3 、3.124g / cm 3 , S1 and S2 are 19.43m respectively 2 / g, 0.713m 2 / g.

[0075] The relationship between the three peak intensities of the XRD spectrum of the active material A is: ①I a1 / I a2 =1.19, F a1 / F a2 =0.94,②I a1 / I a3 =1.27, F a1 / F a3 =1.02;

[0076] Satisfies the following relationship: 0.99≤I a1 / I a2 ≤1.39, 0.74≤F a1 / F a2 ≤1.14, 1.07≤I a1 / I a3 ≤1.47, 0.82≤F a1 / F a3 ≤1.22;

[0077] Among them, I a1 , I a2 , I a3 are the intensity of the first, second and third strongest peaks of active substance A, respectively, and F a1 、F a2 、F a3 are the half-peak widths of the first, second and third strongest peaks of active substance A, respectively;

[0078] The relationship between the three peak intensities of the XRD spectrum of the B active material is: b1 / I b2 =1.45, F b1 / F b2 =0.81,②Ib1 / I b3 =3.61, F b1 / F b3 =0.91,

[0079] The three strongest peaks satisfy the following relationship: 1.23≤I b1 / I b2 ≤1.63, 0.6≤F b1 / F b2 ≤1.0,3.45≤I b1 / I b3 ≤3.85, 0.67≤F b1 / F b3 ≤1.07;

[0080] Among them, I b1 , I b2 , I b3 are the intensity of the first strong peak, the intensity of the second strong peak, and the intensity of the third strong peak of the B active substance, respectively. b1 、F b2 、F b3 are the half-value width of the first strong peak, the half-value width of the second strong peak, and the half-value width of the third strong peak of the B active substance, respectively.

[0081] The positive electrode material in this embodiment is used to prepare a lithium ion battery. During the preparation of the lithium ion battery, the positive electrode coating double-sided density is 372g / m 2 The compaction density of the positive electrode sheet after roller pressing is 2.5g / cm 3 The electrolyte injection coefficient h is 3.6, the ratio q of the negative electrode capacity to the positive electrode capacity of the lithium ion battery is 1.08, and the ratio of h to q is 3.3.

[0082] Example 3

[0083] The difference from Example 1 is that n is 1, and the rest is the same as Example 1.

[0084] Example 4

[0085] The difference from Example 1 is that n is 0.1, and the rest is the same as Example 1.

[0086] Example 5

[0087] The difference from Example 2 is that n is 1, and the rest is the same as Example 2.

[0088] Example 6

[0089] The difference from Example 2 is that n is 9, and the rest is the same as Example 2.

[0090] Comparative Example 1

[0091] The difference from Example 1 is that n is 1.3, and the rest is the same as Example 1.

[0092] Comparative Example 2

[0093] The difference from Example 2 is that n is 0.25, and the rest is the same as Example 2.

[0094] Comparative Example 3

[0095] The positive electrode material is the active material A in Example 1, and the preparation method of the lithium ion battery is the same as that in Example 1.

[0096] Comparative Example 4

[0097] The positive electrode material is the active material B in Example 2, and the preparation method of the lithium ion battery is the same as that in Example 1.

[0098] Comparative Example 5

[0099] The difference from Example 1 is that the active material A has D90 = 1.52 μm, D50 = 0.9 μm, D10 = 0.4 μm, (D90-D50) / (D90-D10) = 1.2, (D50-D10) / (D90-D50) = 0.81, and the particle size distribution does not satisfy the following relationships: (D90-D50) / (D90-D10) ≤ 0.96; 0.03 ≤ (D50-D10) / (D90-D50) ≤ 0.24;

[0100] The rest are the same as in Example 1.

[0101] Comparative Example 6

[0102] The difference from Example 1 is that D90 of active substance B is 6.5 μm, D50 is 3.6 μm, D10 is 0.9 μm, (D50-D10) / (D90-D10) is 0.48 and (D50-D10) / (D90-D50) is 0.93, and the particle size distribution does not satisfy the following relationship: (D50-D10) / (D90-D10)≤0.40; 0.35≤(D50-D10) / (D90-D50)≤0.75.

[0103] The rest are the same as in Example 1.

[0104] Comparative Example 7

[0105] The difference from Example 1 is that the relationship between the three peak intensities of the XRD spectrum of the active material A is: ①I a1 / I a2 =0.9, F a1 / F a2=0.68,②I a1 / I a3 =0.98, F a1 / F a3 =0.76;

[0106] The three strongest peaks do not satisfy the following relationship: 0.99≤I a1 / I a2 ≤1.39, 0.74≤F a1 / F a2 ≤1.14, 1.07≤I a1 / I a3 ≤1.47, 0.82≤F a1 / F a3 ≤1.22;

[0107] The rest are the same as in Example 1.

[0108] Comparative Example 8

[0109] The difference from Example 1 is that the physical property parameters of the active material A and the active material B do not satisfy the following relationship: 0.95≤(T1*T2*S1*S2) / (D1*D2*P1*P2)≤1.15;

[0110] Wherein, T1 and T2 are the tap densities of active material A and active material B, respectively; D1 and D2 are the D50 of active material A and active material B, respectively; P1 and P2 are the powder compaction densities of active material A and active material B, respectively; S1 and S2 are the specific surface areas of active material A and active material B, respectively. Specifically, the relevant parameters related to active material A in this comparative example have changed: T1 and T2 are 0.45 g / cm 3 、1.93g / cm 3 , D1 and D2 are 0.55μm and 3.917μm respectively, P1 and P2 are 2.20g / cm 3 、3.127g / cm 3 , S1 and S2 are 22m2 / g and 0.716m 2 / g.

[0111] The rest are the same as in Example 1.

[0112] Comparative Example 9

[0113] The difference from Example 1 is that the electrolyte injection coefficient h is 2.3, the ratio q of the negative electrode capacity to the positive electrode capacity of the lithium ion battery is 1.08, and the ratio of h to q is 2.13. The rest is the same as Example 1.

[0114] Experimental example

[0115] The batteries prepared in Examples 1-6 and Comparative Examples 1-9 were tested for ultimate compaction density, full electric capacity, rate performance, capacity retention rate, cycle retention rate and cycle gas production, and the results are shown in Table 1.

[0116] As can be seen from Table 1, the lithium-ion batteries prepared using the cathode materials of Examples 1-6 simultaneously exhibit high full-charge specific capacity, high capacity retention, excellent cycle performance, and excellent safety performance. This indicates that at the appropriate blending ratio, active material A effectively coats active material B, reducing its side reactions and stabilizing the interface. Furthermore, at the appropriate blending ratio, active material B increases the energy density of active material A, enhances rate capability, reduces Mn dissolution, and improves storage and cycle performance.

[0117] Compared with Example 1, Example 3 and Example 4, Comparative Example 1 shows that the capacity retention rate, cycle retention rate and cycle gas production of the lithium-ion battery deteriorate seriously due to the excessive proportion of ternary materials. Compared with Example 2, Example 4 and Example 5, Comparative Example 2 shows that the capacity retention rate, cycle retention rate and cycle gas production of the lithium-ion battery also deteriorate seriously due to the low proportion of ternary materials. Compared with Example 4, Comparative Example 3 shows that at the boundary mixing ratio, a small amount of ternary material (active material B) is mixed into the lithium manganese iron phosphate material (active material A). Since the ternary material ions diffuse faster, the rate performance can be improved, and the storage performance and cycle performance can be improved more significantly. Compared with Example 6, at the boundary mixing ratio, a small amount of lithium manganese iron phosphate material (active material A) is mixed into the ternary material (active material B). Since the lithium manganese iron phosphate material improves the interface of the ternary material and reduces side reactions, the cycle performance can be effectively improved. From the above analysis, it can be seen that when the lithium iron manganese phosphate material (active substance A) and the ternary material (active substance B) are mixed, it is necessary to determine the mass ratio n of the ternary material and the lithium iron manganese phosphate material in the positive electrode material based on the range of the ratio k of the actual gram capacity of the ternary material and the lithium iron manganese phosphate material. Specifically, when k is below 1.34, n is 1 to 9; when k is greater than 1.34, n is 0.1 to 1, so as to avoid the following situation: due to improper mixing ratio of the two materials, the lithium-ion battery made using the positive electrode material is prone to problems such as low capacity retention rate, low cycle retention rate, and serious cycle gas production.

[0118] As can be seen from Table 1, compared with Example 1, the full-charge capacity of the lithium-ion battery in Comparative Example 5 is reduced and the rate performance is poor. This is because the particle size distribution of active material A changes, with more large particles and poorer conductivity, resulting in a reduction in the full-charge capacity of the battery and poorer rate performance.

[0119] Compared with Example 1, Comparative Example 6 showed decreased lithium ion capacity retention, decreased cycle retention, and increased cycle gas production. This was due to changes in the particle size distribution of the B active material, resulting in more small particles and more severe side reactions, leading to decreased capacity retention, decreased cycle retention, and increased cycle gas production.

[0120] Compared with Example 1, the lithium-ion battery in Comparative Example 7 has a lower electrode compaction density, a lower capacity retention rate, a lower cycle retention rate, and an increased cycle gas generation. This is due to the poorly developed crystal structure of active material A.

[0121] Compared with Example 1, the electrode compaction density of the lithium-ion battery in Comparative Example 8 is significantly reduced.

[0122] Compared with Example 1, the capacity retention rate and cycle retention rate of the lithium ion battery in Comparative Example 9 are reduced.

[0123] In summary, when the lithium manganese iron phosphate material (A active material) and the ternary material (B active material) are blended, it is necessary to determine the mass ratio n of the ternary material and the lithium manganese iron phosphate material in the positive electrode material based on the range of the ratio k of the actual gram capacity of the ternary material and the lithium manganese iron phosphate material. Specifically, when k is below 1.34, n is 1 to 9; when k is greater than 1.34, n is 0.1 to 1, so as to avoid the following situation: due to the improper blending ratio of the two materials, the lithium ion battery made with the positive electrode material is prone to problems such as low capacity retention rate, low cycle retention rate, and severe cycle gas production. In order to make the lithium ion battery have high energy density, high capacity retention rate, better cycle performance and better safety performance at the same time, in addition to controlling the appropriate blending ratio, it is also necessary to strictly control the particle size distribution, crystal structure, tap density, powder compaction density, specific surface area, etc. of the two blended materials.

[0124] Table 1

[0125] Some of the lithium ion performance testing methods involved in the embodiments of the present invention are as follows:

[0126] Rate Performance: Charge cells according to the requirements for cycle life requirements and test methods for power batteries for electric vehicles in GB / T 31486-2015. After two cycles at 0.33C constant capacity, use the second constant capacity as the 0.33C discharge calibration capacity. Then, cycle 0.33C charge and 3C discharge for two cycles. Use the second capacity as the 3C discharge calibration capacity. Rate performance is quantified by the ratio of the 3C to 0.33C calibration capacities.

[0127] Cycle test: Carry out cycle test in accordance with the cycle life test requirements of GB / T 31484-2015 "Cycle life requirements and test methods for power batteries for electric vehicles", taking the capacity retention rate after 500 cycles and the gas production after 500 cycles.

[0128] High-temperature storage performance test: The fully charged battery was stored in a 60°C constant temperature box for 60 days, and the capacity retention rate and capacity recovery rate were measured.

[0129] Ultimate compaction density test: The positive electrode sheet is rolled to measure the compaction density of the positive electrode sheet in the critical state before brittle failure.

[0130] Full-electric capacity test: Charge the battery cells according to the requirements of GB / T 31486-2015 "Cycle life requirements and test methods for power batteries for electric vehicles". After two cycles at 0.33C constant capacity, use the second cycle constant capacity as the full-electric capacity.

[0131] In addition, it should be noted that although the embodiments of the present invention are disclosed above, the scope of protection of the embodiments of the present invention is not limited thereto. Those skilled in the art may make various changes and modifications without departing from the spirit and scope of the embodiments of the present invention, and such changes and modifications will fall within the scope of protection of the embodiments of the present invention.

Claims

1. A positive electrode material, including w1 parts of active material A Li i1 Mn x1 Fe y1 PO4M f1 and w2 parts of B active material Li i2 Ni x2 Co y2 Mn z O2H f2 , in, i1 is 0.95 to 1.1, the ratio of x1 to y1 is 0.5 to 4, the sum of x1 and y1 is 1, f1 is 200 ppm to 3000 ppm, and M includes at least one of V, Al, Mo, Zr, Mg, Ti, W, Sr, Cr, La and Ce; i2 is 0.95-1.1, the sum of x2, y2 and z is 1, f2 is 200 ppm to 8000 ppm, and H includes at least one of Al, Zr, Ti, Mg, Sr, W, Y, Nb, Ca, Mo, B, F, Ge, Sn, Ce and Ta; The actual gram capacity of the active substance A is c1, the actual gram capacity of the active substance B is c2, the ratio of c2 to c1 is k, and the ratio of w2 to w1 is n; when k is less than or equal to 1.34, n is 1 to 9; when k is greater than 1.34, n is 0.1 to 1.

2. The positive electrode material according to claim 1, wherein The D50 of the active substance A is 0.2-5 μm, and the specific surface area is not higher than 25 m 2 / g, the D50 of the B active substance is 2 μm to 13 μm, and the specific surface area is not higher than 1.5 m 2 / g.

3. The positive electrode material according to claim 2, wherein The particle size distribution of the active substance A satisfies the following relationship: (D90-D50) / (D90-D10)≤0.96; 0.03≤(D50-D10) / (D90-D50)≤0.

24.

4. The positive electrode material according to claim 2, wherein The particle size distribution of the B active substance satisfies the following relationship: (D50-D10) / (D90-D10)≤0.40; 0.35≤(D50-D10) / (D90-D50)≤0.

75.

5. The positive electrode material according to claim 1, wherein The physical property parameters of the A active material and the B active material satisfy the following relationship: 0.95≤(T1*T2*S1*S2) / (D1*D2*P1*P2)≤1.15; In the formula, T1 and T2 are the tap densities of the active material A and the active material B, respectively, D1 and D2 are the D50 of the active material A and the active material B, respectively, P1 and P2 are the powder compaction densities of the active material A and the active material B, respectively, and S1 and S2 are the specific surface areas of the active material A and the active material B, respectively.

6. The positive electrode material according to claim 1, wherein The three strong peaks of the XRD spectrum of the active material A satisfy the following relationship: 0.99≤I a1 / I a2 ≤1.39,0.74≤F a1 / F a2 ≤1.14,1.07≤I a1 / I a3 ≤1.47, 0.82≤F a1 / F a3 ≤1.22; In the formula, I a1 ,I a2 ,I a3 are the intensity of the first strong peak, the intensity of the second strong peak, and the intensity of the third strong peak of the active substance A, respectively, and F a1 、F a2 、F a3 are respectively the half-peak width of the first strong peak, the half-peak width of the second strong peak, and the half-peak width of the third strong peak of the A active substance; The three strong peaks of the XRD spectrum of the B active material satisfy the following relationship: 1.23≤I b1 / I b2 ≤1.63,0.6≤F b1 / F b2 ≤1.0,3.45≤I b1 / I b3 ≤3.85,0.67≤F b1 / F b3 ≤1.07; In the formula, I b1 ,I b2 ,I b3 are the intensity of the first strong peak, the intensity of the second strong peak, and the intensity of the third strong peak of the B active substance, respectively, and F b1 、F b2 、F b3 They are respectively the half-peak width of the first strong peak, the half-peak width of the second strong peak, and the half-peak width of the third strong peak of the B active substance.

7. A positive electrode sheet, comprising the positive electrode material as described in any one of claims 1 to 6.

8. A lithium ion battery comprising the positive electrode sheet as claimed in claim 7.

9. The lithium ion battery according to claim 8, wherein: The compaction density of the positive electrode sheet is 2.0 g / cm 3 To 3.6g / cm 3 .

10. The lithium ion battery according to claim 9, wherein: The electrolyte injection coefficient of the lithium ion battery during the preparation process is h, the ratio of the negative electrode capacity to the positive electrode capacity of the lithium ion battery is q, and the ratio of h to q is 2.43 to 3.48.

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