I think the statement "half man and half animal" is a derogatory interpretation of the traditional Christian belief that God created man as a special type of creature, fully spiritual and existing in a material body (as Christ is fully man and fully God, so man is not divided in his materiality and spirituality).
But if I had to guess, I think Feuerbach is just criticizing Christians for being occupied with spiritual pursuits. I would suppose he thinks this interferes with their ability to love their fellow man, but Christians believe this pursuit actually enhances their love for man.
Back on topic: I cannot find any scripture or material from the church fathers that describes man as "half animal and half angel" specifically. Here is what I did find:
(All biblical passages are in the NIV and taken from https://www.biblegateway.com)
You have made them a little lower than the angels and crowned them with glory and honor. You made them rulers over the works of your hands; you put everything under their feet: all flocks and herds, and the animals of the wild
Let us make mankind in our image, in our likeness, so that they may rule over the fish in the sea and the birds in the sky, over the livestock and all the wild animals
Daniel 4:16 This bit deserves some background, King Nebuchadnezzar had a dream and his dream is fulfilled as a punishment given to him so that he might know God. Notice the phrases uses in the description of the dream:
let him graze with the beasts on the grass of the earth. Let his heart be changed from that of a man, Let him be given the heart of a beast, And let seven times pass over him.
Then the prophecy comes true in verse 31:
“King Nebuchadnezzar, to you it is spoken: the kingdom has departed from you! ... he was driven from men and ate grass like oxen; his body was wet with the dew of heaven till his hair had grown like eagles’ feathers and his nails like birds’ claws.
1 Corinthians 15:39-42
All flesh is not the same flesh: but there is one kind of flesh of men, another flesh of beasts, another of fishes, and another of birds. There are also celestial bodies, and bodies terrestrial ... And as we have borne the image of the earthy, we shall also bear the image of the heavenly. ... we shall all be changed, ... for the trumpet shall sound, and the dead shall be raised incorruptible, and we shall be changed. For this corruptible must put on incorruption
I didn't have a bunch of time to track down a lot of writings from the church fathers on Christian anthropology, but New Advent has St. Gregory of Nyssa's On the Making of Man which seems to be suited to this subject (http://www.newadvent.org/fathers/2914.htm). In many parts of this work St. Gregory expounds on the uniqueness and glory of mankind's creation. Not once does he characterize man as being half animal, but stresses how beautiful creation is and how man is the crowning jewel of that creation.
So let address some philosophical differences between Christianity and the utilitarian materialist ideology that the quote above teaches (I'm not familiar with Feuerbach's work). Christianity teaches that man is unique in that he reflects the divine image and possesses will and reason. The doctrine of the incarnation teaches us that material nature is not in conflict with divinity, but that that which is material can be divine and wholly good, and is purposed to be so (a famous quote from some church father is that man becomes by grace what God is by nature).
A man being animal is not completely out of the question in Christian teaching; but this happens by the destruction of that man's humanity, the annihilation of his person by the withdrawal of the grace of God (as happened to King N). Man is purposed to move through and fulfill his materialness so that he can be resurrected incorruptible (as Paul teaches).
Feuerbach's quote above does not explain how man is unique from creation (what is the difference between an animal and a person?), or what his purpose is. But it does call Christians to abandon their spirituality for more practical aims.
If his accusation is that Christians believe in the spiritual realm as the ultimate reality, then I would say that his assertion is absolutely correct (provided it is also understood that Christians believe they need to care for and love all of creation to attain spiritual blessedness).
So he is expressing a view antithetical to Christianity. Christians believe that man can become a true "person" by being spiritual. Feuerbach teaches that man can become a true "person" by abandoning his spirituality. I think his statement is correct in a sense, Christians are part angel because they worship God and part animal because they live on earth, but it isn't how a Christian would put it.
As a side note Dostoevsky gives a great picture of ideologies much like this in his work Demons. The only antithesis offered in that work to the flood of materialist ideology is one character experiencing the birth of his wife's child in which he is filled with joy which is juxtaposed against the barren heartlessness of the progressive and revolutionary characters.